5. Evolution of organic characters (2002)
5.1. The biotic relation frame
5.1. The biotic relation frame
5.2. The organization
of biochemical processes
5.3. The character of biotic processes
5.4. The secondary characteristic of organisms
5.6. The gene pool
5.7. Does a species correspond with a character?
No doubt, 1859 was the birth year of modern biology. Charles Darwin and Alfred Wallace were neither the first nor the only evolutionists, and their path was paved by geologists in the preceding
century establishing that the earth is much older than was previously perceived, and that many animals and plants living in prehistoric times are now extinct.
The publication of Darwin’s On the origin of species by means of natural selection draw much attention, criticism, and approval. In contrast, Gregor Mendel’s discovery in 1865 of the laws called after him, which would become the basis
of genetics, was ignored for 35 years. The synthesis of Darwin’s idea of natural selection with genetics, microbiology, and molecular biology (circa 1930) constitutes the foundation of modern biology.
This chapter applies the relational character theory, introduced in chapter 1, to living beings and life processes. The genetic relation, leading to renewal and ageing, is the primary characteristic of living subjects (5.1). I investigate
successively the characters of organized and of biotic processes (5.2, 5.3), of individual organisms (5.4) and of populations and their dynamic evolution (5.5, 5.6). For the time being, I shall take for granted that a species corresponds to a character. Section
5.7 deals with the question of whether this assumption is warranted.
Life presupposes the existence of inorganic matter, including the characters typified by the relation frames of number,
space, motion, and interaction. Organisms do not consist of other atoms than those occurring in the periodic system of chemical elements. All physical and chemical laws are unrestrictedly valid for living beings and life processes, taking into account that
an organism is not a physically or chemically closed system.
Both in living organisms and in laboratory situations, the existence of organized and controlled chemical processes indicates
that biotic processes are not completely reducible to physical and chemical ones. In particular, the genetic laws for reproduction make no sense in a physical or chemical context. Rather, they transcend the physical and chemical laws without denying these.
For the biotic relation frame the
genetic law is appropriate. Each living organism descends from another one, and all living organisms are genetically related. This also applies to cells, tissues, and organs of a multicellular plant or animal. Its descent determines the function of
a cell, a tissue, or an organ in an organism, as well as the position of an organism in taxonomy. The genetic law constitutes the universal relation frame for all living beings. Empirically, it is amply confirmed, and it is the starting point of major branches
of biological research, like genetics, evolution theory, and taxonomy. However, in physical and chemical research, the genetic law only plays a part in biochemistry and biophysics.
genetic order is more than a static relationship. It has the dynamics of innovation and ageing. Renewal is a characteristic of life, strongly related to sexual or asexual cell division, to growth and differentiation. The individual life cycle of fertilization,
germination, growth, reproduction, ageing, and dying is irreversible. Rejuvenation occurs in a series from one generation to the next, and between cells in a multicellular organism.
A population goes through periods of rise, blooming, regress, and extinction. Speciation implies innovation as well.
Each living being descends from another living being. The law statement, omne vivum e vivo, is relatively recent. Even in the nineteenth century, generatio spontanea was accepted as a possibility. Empirical and theoretical
research have led to the conviction that life can only spring from life. The theory of evolution does not
exclude spontaneous generation entirely, for that would constitute the beginning of the biotic evolution. It might even be possible that the two kingdoms of prokaryotes arose independently. In contrast, there are good reasons to assume that eukaryotic cells
have evolved from the prokaryotes, and multicellular plants, fungi, and animals from unicellular eukaryotes.
Most biologists accept a stronger law than omne vivum e vivo. It
states that all living beings are genetically related, having a common ancestry. This law, to be called the genetic law, is hard to prove. Paleontological research alone does not suffice to demonstrate that all organisms have the same ancestors, but it achieves support from other quarters. The argument that all living beings depend on the same set of four
or five nucleic acids and twenty amino acids is not strong. Perhaps no other building blocks are available. But in eukaryotes these molecules only occur in the laevo variant, excluding the mirror-symmetric dextro variant. These two are energetically equivalent,
and chemical reactions (as far as applicable) always produce molecules of the two variants in equal quantities. In the production of amino acids, similar DNA and RNA molecules are involved. In widely differing organisms, many other processes proceed identically. Moreover, all plants, animals, and fungi consist of cells, although there are large differences between prokaryotic
and eukaryotic cells, as well as between plant and animal cells. Prokaryotic cells are more primitive and much smaller than eukaryotic cells, and the cell wall is in plants thicker and more rigid than in animals.
The fundamental laws of the universal relation frames cannot be logically derived from empirical evidence, even if this is abundantly available. The laws of thermodynamics, the mechanical conservation laws, and the law of inertia are
no more provable than the genetic law. Such fundamental laws function as axioms in a theory, providing the framework for scientific research of characters. In this sense, the genetic law has proved to be as fruitful as the generally valid physical and kinetic
laws. This does not mean that such laws are not debatable, or void of empirical content. On the contrary, the law of inertia was accepted in the seventeenth century only after a long struggle with the Aristotelian philosophy of nature, from which science had
to be emancipated. The law of conservation of energy and the Second Law of thermodynamics were accepted only about 1850. Similarly, only in the twentieth century the genetic law was recognized after laborious investigations. In all these cases, empirically
sustained arguments ultimately turned the scale.
With respect to the biotic relation frame, the theory of evolution is as general as thermodynamics is with respect to physical and chemical
relations. Both theories concern aggregates, but they are nevertheless indispensable for understanding the characters of individual things and processes. The main axioms of evolution theory are the genetic law and laws for natural selection with respect to
populations. In general terms, the theory of evolution explains why certain species can maintain themselves
in their environment and others cannot, pointing out the appropriate conditions. In specific cases, the evolution theory needs additional data and characteristic laws, in order to explain why a certain species is viable in certain circumstances. Also in this
respect, evolution theory is comparable to thermodynamics.
The genetic law lies at the basis of biological taxonomy. Like plants and fungi, as well as protists and prokaryotes, animals are subject to biotic laws,
but I shall assume that they are primarily characterized by another relation frame, to be called psychical. Within their generic psychic character, a specific organic character is interlaced. Genetic relations primarily characterize all other living
beings and life processes. Each biotic process is involved with replication (5.3), and the nature of each living being is genetically determined (5.4). Within an organism, physical and chemical processes have the tertiary disposition to function in biotic
processes (5.2). Living beings support symbiotic relations leading to evolution (5.5).
The genetic law is a leading principle of explanation for taxonomy and the modern species concept.
The universal relation frames allow us of identifying any thing or event, to establish its existence and change, and to find its temporal relations to other things and events. In principle, the genetic law allows of the possibility to order all organisms into
a biological taxonomy. The empirical taxonomy does not originate from human thought but from living nature. Its leading principle is not logical but biological. A logical, i.e., deductive classification is based on a division of sets into subsets, considering
similarities and differences. It descends logically from general (the kingdoms and phyla) to specific (the species). In contrast, the biological ordering depends on genetic descent, ascending inductively from species to the higher categories.
Genetic relations can be projected on the preceding relation frames, in this chapter to be indicated by the italics a-d. On the different levels of taxonomy, a species, and a multicellular
organism, these mappings can be distinguished as follows.
a. A lineage is a serial projection of the genetic order on the quantitative relation frame. Within a species one finds the linear relation of parent to offspring. Within a multicellular organism the serial order concerns each line of replicating
cells. By counting the intermediary
specimens, it is possible to establish the genetic relation between two individuals, organs, or cells, that are serially connected.
lineages are mutually connected by common ancestry. Therefore species, organs, or cells having no serial relation may be related by kinship, the genetic relation between
siblings, cousins, etc. Kinship of parallel lineages is to be considered a spatial expression of the genetic relation. Each branching means a new species, a new individual, a new organ, or a new cell. In taxonomy, biologists establish kinship between species
on the basis of similarities and differences. These concern shape (morphology), way of life (physiology), development of an organism (in particular embryology), the manner of reproduction, and nowadays especially comparing DNA, RNA, or the proteins they produce. Kindred lineages are connected in
a cladogram, a diagram showing the degree of kinship between species. If an organism has several descendants, the lineage branches within a species. In sexual reproduction
lineages are connected and each organism has two parents, four grandparents, etc. Within an organism cell division causes branching. In a plant, fungus, or animal, recently branched cells lie close to each other. The larger the distance between two cells,
the smaller is their kinship.
c. Genetic development may be considered the kinetic projection of the order
of renewal and ageing. Temporal relations are recognizable in the generation difference as a biotic measure mapped on kinetic time. It is the time between two successive bifurcations of a species, between the germination of a plant and that of its seeds, or
between two successive cell divisions. If timing is taken into account, a cladogram becomes a phylogenetic tree. Between two splits a population evolves. From germination to death an organism develops, and cells differentiate and integrate into tissues and
d. The dynamic force of evolution within a species and the splitting of species consist of competition and natural
selection. These may be considered projections of the genetic relation on the physical. Between plants, the competition concerns physical and chemical resources for existence, between fungi and animals organic ones as well. Competition is a repulsive
force, to use a physical term. Besides natural selection, accidental processes lead to genetic changes, mostly in small isolated populations. This phenomenon is called ‘random genetic drift’ or ‘inbreeding’ in common parlance. Breeders
use it to achieve desirable plant or cattle variations. There are attractive forces as well. Only within a species, sexual reproduction is the most innovative form of replication. Sexual interaction may be considered a specific physical expression of the genetic
relation. Within an organism, neighbouring cells influence each other during their differentiation and integration.
These projections give rise to four types, each of organized chemical
processes (5.2), biotic processes (5.3), biotically qualified thing-like characters (5.4), and their aggregates (5.5, 5.6).
5.2. The organization of biochemical processes
In each living being, many organized biochemical processes take place, having a function in the life of a cell, a tissue, an organ, or an organism. The term organism for an individual
living being points to its character as an organized and organizing unit. The organism has a temporal existence. It emerges when the plant germinates, it increases in largeness and complexity during its development, it ages and after its death it falls apart.
An organized unit is not necessarily a living being. A machine does not live, but it is an organized whole, made after a design. A machine does not reproduce itself and is not genetically related
to other machines. Because human persons design a machine, its design cannot be found in the machine itself. In a living organism, the natural design is laid down in the genome, the ordered set of genes based on one of more DNA molecules.
The organism transfers the design from cell to cell and from generation to generation. The natural design changes because of mutation at the level of a single cell, because of sexual interaction at the level of organisms, or caused by natural selection at
the level of a population. It is bound to general and specific laws determining the conditions under which the design is executable or viable. A design is the objective prescription for a biotic character. It is a chemical character having a tertiary biotic
The processes to be discussed in the present section are primarily physically qualified, and some of them can be organized in a laboratory or factory. Their disposition
to have a function in biotic processes is a tertiary characteristic (5.3).
are assembled according to a design. Although the concept of a lineage points to a relation between living beings, there is an analogy on the molecular level. This refers to the assemblage of molecules according to a genetic design as laid down in the DNA
molecules. The DNA composition is partly species specific, partly it is unique for each individual living being.
The natural design for an organism is laid down in its genome, the genetic
constellation of the genes in a specific sequence. The DNA molecules are the objective bearers of the genetic design, which is the genotype determining the phenotype, that is the appearance of a living being. Each organism has its own genome, being the objective
expression of the species to which it belongs as well as of its individuality. Like the DNA molecules, the genome is mostly species specific.
A DNA molecule consists of a characteristic
sequence of bases (nucleotides) of nucleic acids indicated by the letters A (adenine), C (cytosine), G (guanine) and T (thymine).
DNA is the start of the assembly lines of the molecules having a function in life processes. Three nucleotides form the design for one of the twenty possible amino acids. An RNA molecule is a replica of the part of the DNA molecule corresponding to a single
gene. Mediated by an RNA molecule each gene designs a polypeptide or protein consisting of a characteristic sequence of amino acids.
Some proteins are enzymes acting as catalysts in these and other material transformations.
Although a great deal of the assembly of molecules takes place according to a genetically determined pattern, interaction with the surroundings takes place as well. The environment is first of all
the cell plasma, the more or less independent specialized organelles and the cell wall, in which many specific biochemical processes occur. Second, via the cell wall a cell is in contact with the physical and chemical environment. Third, in multicellular organisms
the environment includes other cells in the immediate neighbourhood. Finally, only animal cells exert some kind of action at a distance (6.1).
To a large extent, the environment determines
which genes or combinations of genes are active, being selectively switched on or off. The activity of genes in a multicellular organism depends on the phase of development. The genome acts in the germination phase differently than in an adult plant, in a
root otherwise than in a flower. The genetic constellation determines the growth of an organism. Conversely, the genetic action depends on the development of the plant and the differentiation of its cells.
Therefore, DNA is not comparable to a code, a blueprint, a map or diagram in which the phenotype is represented on a small scale. Rather, it is an extensive prescription, a detailed set of instructions
for biochemical processes.
enormous variation of molecules is possible because of the equality of the atoms and the uniformity of chemical bonding. This is comparable with the construction of machines. It is easy to vary machines if and as far as the parts are standardized and hence
exchangeable. This applies to the disparity of organisms as well. The organization of a plant or an animal consists partly of standardized modules, some of which are homologous in widely different organisms. Such modules exist on the level of molecules (there
are only twenty different amino acids, with an enormous variation in combinations), genes (standardized combinations of genes), cells (the number of cell types is restricted to several hundreds), tissues and organs. For evolutionary innovations, the existence
of exchangeable parts having a different function in different combinations and circumstances is indispensable.
b. The biotic functions of molecules depend on their shape. Although the macromolecules occurring in living
beings have an enormous diversity, they have much in common as well. Polymers are chains of monomers connected by strong covalent bonds (5.3). Polysaccharides consist of carbohydrates (sugars), polypeptides are constructed from amino acids, and nucleic acids
consist of nucleotides. The lipids (fats, oils and vitamins) constitute a fourth important group of large molecules. Lipids are not soluble in water. Lipids are not characterized by covalent bonds but by the weaker Van der Waals bonding. Phospholipids are
the most important molecules in biotic membranes. In the double cell wall the molecules are at one end hydrophilic (attracting water), at the other end hydrophobic (repelling water). In the assembly of polymers, water is liberated, whereas polymers break down
by hydrolysis (absorption of water).
All organisms apply the same monomers as building blocks of polymers. In contrast, the polymers, in particular the polypeptides and nucleic acids,
are species specific. The twenty different amino acids can be connected to each other in each order and in large amounts. As a consequence, the diversity of proteins and their functions is enormous.
Polymers do not only differ because of their serial composition, but in particular by their spatial shape. Like all molecules, they are primarily physically qualified and secondarily spatially founded. DNA’s double helix structure plays a part
in its replication in cell division. Also other macromolecules display several spatial structures simultaneously. For the functioning of a protein as an enzyme, its spatial structure is decisive.
Each biochemical process has to overcome an energy barrier (5.6). Increasing the temperature is not suitable, because it accelerates each chemical process and is therefore not selective enough. Catalysis by specialized proteins (enzymes) or RNA molecules
(ribozymes) is found in all organisms. In plants, the enzyme rubisco is indispensable for photosynthesis.
The polymers have various functions in an organism, like energy storage, structural
support, safety, catalysis, transport, growth, defence, control, or motion. Only nucleic acids have a function in the reproduction of cells and organisms.
c. The genetic development of a living being depends on metabolism, a transport process. A cell can only live and replicate because of a constant stream of matter and energy through various membranes. A unicellular
organism has direct contact with its environment, in which it finds its food and deposits its waste. This also applies to a multicellular organism consisting of a colony of independently operating cells, like many algae. These organisms’ ideal environment
is salt water, followed by fresh water and moist situations like mud or the intestines of animals. To colonial organisms, this imposes the constraint that a tissue cannot be thicker than two cells.
Multicellular fungi, plants, or animals need internal transport of food, energy, and waste, requiring cell differentiation, in which, for instance, the photosynthetic cells lie at the periphery of plants. Metabolism is an organized stream of matter
through the organism. It allows of life outside water. In the atmosphere, oxygen is better accessible than in water, other materials are less accessible.
The cell wall is not merely
a boundary of the cell. Nor is it a passive membrane that would transmit some kinds of matter better than others. Rather, it is actively involved in the transport of all kinds of matter from one cell to another. Membranes have an important function in the
organization of biochemical processes, the assemblage of molecules, the transformation of energy, the transport of matter, the transfer of information, and the processing of signals. Hence, the presence of membranes may be considered a condition for life.
Plant cells are close together, and transport takes place directly from one cell to the other one. A plant cell has at least one intracellular cavity enclosed by a membrane. This is a vacuole,
mostly filled with water, acting as a buffer storage and waste disposal. Animals have intercellular cavities between their cells. Animal cells are connected by proteins regulating the exchange of molecules and information. These proteins play an important
part in the development of the embryo as well.
Passive transport is distinguished from active transport. Passive transport lacks an external source of energy and is caused by diffusion
in a chemical solution or by osmosis if the solution passes a membrane. Some substances pass a membrane
together with proteins acting as carriers. The concentration gradient is the driving force of diffusion. The size and the electric charge of the molecules concerned and the distance to be travelled also influence the diffusion speed. In particular the distance
is a constraint, such that diffusion is only significant within a cell and between two neighbouring cells. To cover larger distances other means of transport are needed.
requires a source of energy, like adenosine triphosphate (ATP). This transport is coupled to carriers and proceeds against a concentration difference like a pump. Endo- or exocytose in eukaryotic cells is the process in which the cell wall encapsulates the
substance to be transported. After the capsule has passed the wall it releases the transported substance. Animal cells have receptors in their wall sensitive for specific macromolecules. Besides, animals have organs specifically designed for transport, for
instance by the circulation of blood.
No organism can live without energy. Nearly all organisms derive their energy directly or indirectly from the sun, by photosynthesis. This process
transforms water, carbon dioxide, and light into sugar and oxygen. This apparently simple chemical reaction is in fact a complicated and well organized process, only occurring in photosynthetic bacteria and in green plants. The product is glucose (a sugar
with six carbon atoms in its molecule), yielding energy rich food for plants and all organisms that feed on plants.
The transformation of energy is a redox reaction. Some molecules oxidize
by donating electrons, whereas other molecules reduce by accepting electrons. The first step is glycolysis (transformation of glucose in pyruvate), which does not require oxygen. Most organisms use oxygen for the next steps (cellular respiration). Other organisms
are anaerobic, transforming energy by fermentation, which is less efficient. In the absence of oxygen, many aerobic cells switch to fermentation. Because nerve cells are unable to do so, they become easily damaged at a shortage of oxygen. Glycolysis, cellular
respiration and fermentation are organized processes with many intermediate steps. The end product consists of ATP and other energy carriers that after transport cede their energy in other chemical reactions.
d. Self-replication of DNA molecules has a function in reproduction. Serving as a starting point for the assemblage of polypeptides,
the DNA molecule has a specific spatial structure. It consists of a double helix of two sequences of nucleotides being each other’s complement, because each adenide (A) in one sequence connects to a thymine (T) in the other one and each cytosine (C)
in one sequence to a guanine (G) in the other. If the DNA molecule consists of two such strings it is called diploid.
The two halves are not identical, even if they look alike. This structure makes the DNA molecule very stable. An RNA molecule, acting as an intermediary between a gene on the DNA molecule and the assemblage of a polypeptide, is haploid. Consisting
of a single helix, it is less stable than DNA. DNA is not always diploid. Many fungi consist of haploid cells. Only during sexual reproduction, their sex cells are diploid.
The DNA molecule
itself is not assembled by another molecule. It has a unique way of self-duplication. Preceding a cell division, the diploid helix unfolds itself and the two haploid halves separate. In sexual cell division (meiosis) the next steps differ from those in the
far more frequent asexual cell division (mitosis).
Mitosis is the asexual form of reproduction for unicellular organisms. It also occurs in the growth of all multicellular organisms.
After the first division of the diploid DNA molecule, each half doubles itself by separating the two sequences and connecting a new complementary base to each existing base. Hence, two new diploid DNA molecules arise, after which the cell splits as well. The
daughter cells are genetically identical to the mother cell.
Meiosis, the sexual cell division, is more varied. In a much occurring variant, the DNA remains haploid after the
first splitting. As a rule, after the second division four daughter cells arise, each with half the DNA. Either all four are sperm cells or one is an egg cell, whereas the other three die or become organelles in the egg cell. Only after the egg cell merges
with a sperm cell of another individual, a new diploid cell arises. This cell has a different composition of DNA, hence a new identity. This is only possible if the two merging DNA halves fit to each other. In most cases this means that the individuals concerned
belong to the same species. In prokaryotes meiosis is often a more complicated process than in eukaryotes.
Cell division is not restricted to DNA replication. The membranes are not formed
de novo but grow from the existing ones. In particular, the cell wall of the original cell is divided among the daughter cells. Life builds on life.
5.3. The character
of biotic processes
Besides the organized biochemical processes there are processes that are typically biotically qualified. In section 5.5, I shall discuss the
genetic changes occurring in a population. Important processes for the dynamic development of an individual organism, to be discussed in the present section, are cell division, spatial shaping, growth and reproduction.
The genetic identity of a living organism as a whole is determined by its genetic contents. Its heredity is expressed in the genes and their material basis, the DNA molecules. All cells of a multicellular organism have the same DNA
configuration and every two living beings have different DNA molecules, except in the case of asexual reproduction. The genes organize the biochemical processes discussed in section 5.2 as well as the biotic processes to be discussed in section 5.3. The genetic
identity as an organizing principle of a living being determines its temporal unity. This unity disappears when the organism dies and disintegrates.
a. Cell division is a biotically qualified process that is quantitatively founded. The cell as a subjective unit multiplies itself. Sexual cell division (preceded by sexual interaction, see below) is distinguished
from the more frequent asexual cell division (5.2). In the case of an eukaryotic cell, the nucleus too is divided into two halves. The other cell bodies, the cell plasma, and the cell wall, are shared out to the daughter cells and supplied by new ones.
Many organisms reproduce asexually. The prokaryotes and protists (mostly unicellular eukaryotes) reproduce by cell division. Many plants do so by self-pollination. Now the daughter has the same
genetic identity as the parent. In this respect they could be considered two spatially separated parts of the same plant. On the one hand, nothing is wrong with this view. Alaska is an integral part of the United States, though it is spatially separated from
the mainland. The primary character determines the temporal unity of an individual, and in the case of a bacterium, a fungus, or a plant, this is its genetic identity. Only after a sexual reproduction the daughter plant is a real new individual, genetically
different from its parents and any other individual. On the other hand, this view counters natural experience, accepting a plant as an individual only if it is coherent. Moreover, in asexual reproduction not only the spatial coherence is lost, but all kinds
of biochemical and biotic interactions as well. This seems to be sufficient to suppose that asexual reproduction gives rise to a new individual.
No single organism is subject to genetic change. Hardly anything can be found that is more stable than the genetic character and the identity of a living being. From its germination to its death,
a plant remains identical to itself in a genetic sense. Only in sexual replication genetic change occurs. Of course, a plant is subject to other changes, both cyclic (seasonal) and during its development in its successive phases of life.
b. The genetic relation is not the only factor determining the biotic position of a living being. For each plant and
every animal, its relation to the environment (the biotope or ecosystem) is a condition of life. First, the environment concerns subject-subject relations. Symbiosis should be considered a spatially founded way of living together. It is found on all
levels of life. Within an eukaryotic cell symbiosis occurs between the cell nucleus and the organelles having their own DNA. In multicellular organisms cells form tissues or organs. In an ecosystem, unicellular and multicellular organisms live together, mutually
dependent, competitive or parasitic.
Second, each organism has a subject-object relation to the physical and chemical surroundings of air, water, and soil. Just like the organized matter
in the plant, the physical environment has a dynamic function in life processes.
Third, the character of plants anticipates the behaviour of animals and human beings. This constitutes
an object-subject relation. By their specific shape, taste, colour, and flavour plants are observable and recognizable by animals as food, poison, or places suited for nesting, hunting, and hiding.
c. The dynamic development of a plant from its germination to adulthood may be considered a kinetically founded biotic process. It is accompanied by differentiation
of cells and pattern formation in tissues, and by relative motion of cells in animals. The growth of a plant is strongly determined, programmed by the genome. In the cell division the DNA does not change, but the genes are differentially switched on and off.
During the growth, cells differentiate into various types, influenced by neighbouring cells.
There are other influences from the environment, for a plant only grows if the circumstances permit it. Most seeds never start developing, because the external factors are not favourable. Even
for a developing plant, the genotype does not determine the phenotype entirely. The development of the plant occurs in phases from cell to cell, in which the phenotype of the next cell is both determined by its genotype and by the phenotype of the preceding
cell and the surrounding cells, as well as by the physical, chemical, and organic environment.
The dynamic development of a plant or animal belongs to the least understood processes
in biology. It starts from a single point, fertilization, and expands into a series of parallel but related
pathways. Sometimes one pathway may be changed without affecting others, leading to a developmental dissociation. Usually such dissociation is lethal, but if it is viable, it may serve as a starting point for evolutionary renewal.
d. Sexual reproduction may be considered a primarily biotically qualified process that is secondarily physically
founded, like a biotic interaction. Two genetically different cells unite, and the DNA splits before forming a new combination of genes (5.2). By sexual reproduction a new individual comes into being, with a new genetic identity.
Contrary to the growth of a plant, reproduction is to a large extent accidental. Which cells unite sexually is mostly incidental. Usually only sex cells from plants of the same species may pair, although hybridization
occurs frequently in the plant kingdom. By their mating behaviour, animals sometimes limit accidents, increasing their chances. Even if a viable combination is available, the probability is small that the seed germinates, reaches adulthood and becomes a fruit
bearing plant. Because the ultimate chance of success is small, a plant produces during its life an enormous amount of gametes. On the average and in equilibrium circumstances, only one fruit bearing descendant survives. The accidental nature and abundance
of reproduction, supplied with incidents like mutation, is a condition for natural selection. But if it would occur in a similar way during the growth of a plant, no plant would ever reach the adult stage. Dynamic development is a programmed and reproducible
process. Sexual reproduction (as well as evolution according to Charles Darwin) is neither.
Fertilization is a biotically qualified process, interlaced with biochemical processes having a biotic function. Moreover, in animals fertilization is interlaced with the psychically qualified mating
behaviour that is biotically founded.
5.4. The secondary characteristic of organisms
Assuming that four relation frames precede the biotic one, we should expect four secondary types of biotically qualified thing-like characters. These are,
respectively, quantitatively, spatially, kinetically, or physically founded. Each type is interlaced with the corresponding type of biotic processes mentioned in section 5.3. Moreover, the characters of different types are interlaced with each other as well.
a. It seems obvious to consider the cell to be the smallest unit of life. Each living being is
either a cell or a composite of cells. However, this conceals the distinction between prokaryotes (bacteria and some algae) and eukaryotes. According to many biologists, this difference is more significant than that between plants and animals.
The oldest known fossils are prokaryotes, and during three-quarters of the history of the terrestrial biosphere, eukaryotes were absent. Prokaryotic cells are more primitive and usually smaller than eukaryotic cells. Most prokaryotes like bacteria are unicellular,
although some colonial prokaryotes like algae exist. The protists, fungi, plants, and animals consist of eukaryotic cells. A bacterium has only one membrane, the cell wall. An eukaryotic cell has several compartments enclosed by a membrane. Besides vacuoles
these are particles like the cell nucleus, ribosomes (where RNA molecules assemble polypeptides), mitochondria (the power stations of a cell), and chloroplasts (responsible for photosynthesis). Prokaryotes have only one chromosome, eukaryotes more than one.
Therefore, biologists consider the prokaryotes to belong to a separate kingdom, or even two kingdoms, the (eu)bacteria and the much smaller group of archaebacteria (archaea).
that the chromosomes in an eukaryotic cell have a prokaryotic character, as well as the genetically more or less independent mitochondria and chloroplasts. Having their own DNA, the latter organelles’ composition is genetically related to that of the
prokaryotes. Therefore, I consider the character of prokaryotes to be primarily biotic and secondarily quantitative.
This may also apply to the characters of the mitochondria, chloroplasts, and chromosomes in an eukaryotic cell, and to the character of viruses as well. None of these can exist as a living being outside a cell, but each has its own character and a recognizable
genetic identity. Their character has the tertiary disposition to become interlaced in that of an eukaryotic
cell. In eukaryotic organisms, reproduction starts in the prokaryotic chromosomes.
spatially founded biotic character is characterized by symbiosis (5.3). The symbiosis of prokaryotes in an eukaryotic cell is called endosymbiosis. In the character of an eukaryotic cell several quantitatively founded prokaryotic characters are encapsulated.
In turn, eukaryotic cells are the characteristic units of a multicellular fungus, plant, or animal. Each
cell has a spatial (morphological) shape, determined by the functions performed in and by the cell.
In colonial plants (thallophytes like some kinds of algae), the cells are undifferentiated.
As in colonial prokaryotes, metabolism takes place in each cell independent of the other cells. In higher organisms, eukaryotic cells have the disposition to differentiate and to integrate into tissues and organs. Both in cell division and in growth, cells,
tissues, or organs emerge having a specific shape. The spatial expression of an organism is found in its morphology, of old a striking characteristic of living beings. Since the invention of the optical microscope in the seventeenth century and the electron
microscope in the twentieth, the structure of a cell is well known.
organisms and organs have a kinetically founded character. Except for unicellular and colonial organisms, each living being is characterized by its dynamic development from the embryonic to the adult phase. Now the replication of cells leads to morphological
and functional differentiation. In a succession of cell divisions, changes in morphology and physiology of cells occur. Their tertiary character takes distance from that of the gametes. This gives rise to differentiated tissues and organs like fibres, the
stem and its bark, roots, and leaves. These have different morphological shapes and various physiological functions. In a differentiated plant, metabolism is an organized process, involving many cells in mutually dependent various ways (5.2). Growth is a biotic
process (5.3). Differentiation enhances the plant’s stability, fitness and adaptive power.
Differentiation concerns in particular the various functions that we find in a plant.
The biological concept of a function represents a subject-object relation as well as a disposition. Something is a biotic object if it has a function with respect to a biotic subject (5.2). Cells, tissues, and organs are biotic subjects themselves.
A cell has the disposition to be a part of a spatially founded tissue, in which it has a function of its own. A tissue has an objective function in a differentiated organ. By differentiation the functions are divided between cells and concentrated in tissues.
In a differentiated plant, chlorophyll is only found in leaves, but it is indispensable for the whole plant. The leaves have a position such that they catch a maximum amount of light.
leads to the natural development from germination to death. The variety in the successive life phases of fertilization, germination, growth, maturing, reproduction, ageing, and natural death is typical for differentiated fungi, plants, and animals.
Although the cells of various tissues display remarkable differences, their kinship is large. This follows from the fact that many plants are able to reproduce asexually by the formation of buds,
bulbs, stolons, tubers, or rhizomes. In these processes, new individuals emerge from differentiated tissues of plants. Grafting and slipping of plants are agricultural applications of this regenerative power.
d. Sexual reproduction appears to be an important specific projection of the genetic relation on the physical and chemical relation frame. This
biotic interaction between two living beings is the most important instrument of biotic renewal. All eukaryotic organisms reproduce by sexual cell division (even if some species reproduce by other means most of the time). In prokaryotes, the exchange of genetic
matter does not occur by sexual interaction, but by the merger of two individuals. Reproduction is a biotic process (5.3), and the part played by DNA replication is discussed in section 5.2.
In the highest developed plants, sexuality is specialized in typical sexual organs, like flowers, pistils, and stamens. Some plant species have separate male and female specimens. In sexually differentiated plants, the sexual relation determines the
genetic cycle, including the formation of seeds. Fertilized seeds can exist some time independent of the parent plant without germinating, for instance in order to survive the winter. Sometimes they are provided with a hard indigestible wall, surrounded by
pulp being attractive food for animals. The animal excretes the indigestible kernel, co-operating in the dispersal of the seeds.
In particular, sexual reproduction is relevant for the
genetic variation within a population. This variation enhances the population’s adaptability considerably. The genetic kinship between individuals in a population is much less than the genetic relation between cells within an individual organism.
The characteristic distinctions between an egg cell and pollen, between male and female sex organs in bisexual plants, and between male and female specimens in unisexual plants, have a function
to prevent the merger of sex cells from the same individual. In bisexual plants self-pollination does occur, but sometimes the genetic cycle is arranged such as to preclude this. Fungi are not sexually differentiated but have other means to prevent self-fertilization.
Within each fungus species several types occur, such that only individuals of different types can fertilize each other.
The above presented distinction of four biotic types of thing-like characters is only the start of their analysis. Real characters almost always consist of an interlacement of differently typed characters.
First, one recognizes the interlacement of equally biotically qualified but differently founded characters. In eukaryotic cells, an interlacement occurs with various organelles having a prokaryotic character. Because the organelles
have various functions, this interlacement leads to a certain amount of differentiation. In all multicellular plants, the character of the cells is interlaced into that of a tissue. In differentiated plants, the character of organs is interlaced with those
of tissues. This concerns both their morphological structure and their physiological functions. The highest developed plants display an interlacement of cells, tissues, leaves, roots, flowers, and seeds. Together they constitute the organism, the
plant’s primary biotic character. The differentiation of male and female organs or individuals is striking.
Second, the biotic organism is interlaced with characters that are not
biotically qualified. First of all, these concern the physically qualified characters of the molecules composing the plant (5.2). Besides we find in a plant kinetic characters, typical motions of the plant as a whole or of its parts. An example is the daily
opening and closing of flowers, or the transport of water from roots to leaves. Each plant and each of its cells, tissues, and organs have typical shapes. By no means these characters are purely physical, chemical, kinetic, or spatial. They are opened up by
the biotic organism in which their characters are encapsulated. Their tertiary biotic disposition is more obvious than their primary qualifying or secondary founding relation frames. They have a function determined by the organism. Unlike cells and tissues,
they do not form parts of the organism, as follows from the fact that they often persist some time after the death of the organism. Everybody recognizes the typical structure of a piece of wood to be of organic origin, even if the plant concerned
is dead for a long time. Wood is not alive, but its physical properties and spatial structure cannot be explained from physical laws only. Wood is a product of a living being, which organism orders the physically qualified molecules in a typically
Third, we encounter the interlacement of the organism with many kinds of biochemical and biotic processes (5.2, 5.3). Whereas physical systems always proceed to an equilibrium
state, an organism is almost never at rest. (A boundary case is a seed in a quasi-stable state). Metabolism is a condition for life. Reproduction, development, and growth of a multicellular organism, and the seasonal metamorphosis of perennial plants, are
examples of biotic processes. Each has its own character, interlaced with that of the organism.
The typology of characters differs from the biotic taxonomy. A relatively recent taxonomy of living beings still distinguished five kingdoms: monera (prokaryotes); protoctista or protista (unicellular and colonial eukaryotic
organisms); fungi; animalia; and plantae. Nowadays the prokaryotes are divided
into the kingdoms of (eu)bacteria and archaebacteria or archaea, differing from each other as much as they differ from the eukaryotes. The protists form a set of mutually hardly related unicellular or colonial eukaryotes. Fungi are
distinguished from plants by having haploid cells most of the time. Being unable to assimilate carbon, they depend on dead organic matter, or they parasitize plants or animals. DNA research reveals that fungi are more related to animals than to plants.
It cannot be expected that the typology discussed in this section would correspond to the biological taxonomy of species. Taxonomy is based on specific similarities and differences and on empirically
found or theoretically assumed lineages and kinship. If the biotic kingdoms in the taxonomy would correspond to the division according to their secondary characteristic, this would mean that the four character types would have developed successively in a single
line. In fact, many lineages evolve simultaneously. In each kingdom the actualization of animal phyla or plant divisions, classes, orders, etc. proceeds in the order of the four secondary character types and their interlacements. However, their disparity cannot
be reduced to the typology based on the general relation frames.
The biological taxonomy, the division of species into genera, families, orders, classes, phyla or divisions, and kingdoms,
is not based on the general typification of characters according to their primary, secondary, and tertiary characteristics. Rather, it is a specific typification, based on specific similarities and differences between species.
Sections 5.2 and 5.3 investigated physical, chemical, and biotic processes
based on projections of the biotic relation frame on the preceding frames. Section 5.4, too, was mainly directed to secondary characteristics of biotic subjects. Now a tertiary characteristic will be considered, the disposition of organisms to adapt to their
environment. Organisms do not evolve individually, but as a population in a biotope or ecosystem. Section 5.5 discusses the laws for populations and aggregates of populations, whereas section 5.6 treats the genome and the gene pool as objective aggregates.
a. A population is a homogeneous aggregate, a spatio-temporally bounded and genetically coherent set of
living beings of the same species. Two sets of organisms of the same species are considered different populations,
if they are spatially isolated and the exchange of genetic matter is precluded. A population as a whole evolves and isolated populations evolve independently from each other.
is a quantitatively founded biotic aggregate, having a number of objective properties open to statistical research, like number, dispersion, density, birth rate, and death rate. These numbers are subject to the law of abundance. Each population produces much
more offspring than could reach maturity. The principle of abundance is a necessary condition for survival and evolutionary change. Competition, the struggle for life, sets a limit to abundance.
Being threatened by extinction, small populations are more vulnerable than larger ones. Nevertheless, they are better fit to adaptation. Important evolutionary changes only occur in relatively
small populations that are reproductively isolated from populations of the same species. As a ‘founder population’, a small population is able to start a new species. Large, widely dispersed populations are evolutionary inert.
b. A biotope or ecosystem is a heterogeneous aggregate. It is a spatially more or less bounded collection
of organisms of different species, living together and being more or less interdependent. The biotic environment or habitat of a population consists of other populations of various species.
A biotope is characterized by the symbiosis of prokaryotes and eukaryotes, of unicellular and multicellular organisms, of fungi and plants. Most biotopes are opened up because animals take part in them, and sometimes because they are organized by human
interference. Biotopes like deserts, woods, meadows, or gardens are easily recognizable.
A population occupies a niche in a biotope. A niche or adaptive zone
indicates the living room of a population. Both physical and biotic circumstances determine a niche, in particular predator-prey relations and the competition about space and food. Each niche is both possible and constrained because of the presence of other
populations in the same area. In general, the geographic boundaries of the habitats of different species will not coincide. Therefore the boundary of a biotope is quite arbitrary.
niche is occupied by at most one population. This competitive exclusion principle is comparable to Wolfgang Pauli’s exclusion principle for fermions (5.2, 5.4). If a population that would fit an occupied niche invades an ecosystem, the result is a conflict
ending with the defeat of one of the two populations. Sooner or later, some population will occupy an empty niche.
If the physical or biotic environment changes, a population can adapt
by genetically evolving or by finding another niche. If it fails it becomes extinct.
c. In each
biotope, the populations depend on each other. Each biotope has its food chains and cycles of inorganic material. Fungi living mainly off dead plants form a kingdom of recyclers.
Many bacteria parasitize living plants or animals, which, conversely, often depend on bacteria. Sometimes the relation is very specific. For instance, a lichen is a characteristic symbiosis of a fungus and a green or blue alga.
The biotic equilibrium in an ecosystem may change by physical causes like climatic circumstances, by biotic causes like the invasion of a new species, or by human intervention. Like a physical equilibrium, the biotic
balance has a dynamic character. If an ecosystem gets out of balance, processes start having the disposition to repair equilibrium or to establish a new equilibrium.
Sometimes the ecological
equilibrium has a specific character, if two populations are more or less exclusively dependent on each other, for instance in a predator-prey relation. If the prey increases its number, the number of predators will grow as well. But then the number of prey
will decrease, causing a decrease of predators. In such an oscillating bistable system, two ‘attractors’ appear to be active.
d. Individual organisms are not susceptible to genetic change, but populations are subject to evolutionary change. Besides competition, the driving force of this dynamic development is natural selection, the engine of evolution.
With each genotype a phenotype corresponds, the external shape and the functioning of the individual plant. Rather than the genotype, the phenotype determines whether a plant is fit to survive in its environment and to reproduce. Fitness depends on the survival
value of an individual plant at short term, and on its reproduction capability and the viability of its offspring.
Fitness is a long-term measure for the ability of a population to maintain and reproduce itself.
Natural selection concerns a population and acts on the phenotype. It has the effect
that ‘the fittest survives’, as Herbert Spencer would have it. The struggle for life is a process
taking place mostly within a population, much less between related populations (if occupying overlapping niches), and hardly ever between populations of different species.
But the evolution of a population depends on the environment, including the evolution of other populations. The phenomenon of co-evolution means that several lineages evolve simultaneously and
mutually dependently. An example is the evolution of seed eating birds and seed carrying plants. The plant depends on the birds for the dispersion of its seeds, whereas the birds depend on the plants for their food. Sometimes, the relation is very specific.
Besides co-evolution, biologists distinguish divergent and convergent evolution of homologous respectively analogous properties.
Homology concerns a characteristic having a common origin. In related species, its function evolved in diverging directions. Analogy concerns a characteristic having a corresponding function but a different origin. The emergence of analogous
properties is called convergent or parallel evolution. The stings of a cactus are homologous to the leaves of an oak, but analogous to the spines of a hedgehog. The wings of a bird and a bat are homologous to each other, but analogous to the wings of an insect.
Light sensitivity or visual power emerged at least forty times independently, hence analogously, but the underlying photoreceptors may have arisen only once, they appear to be homologous.
5.6. The gene pool
The insight that populations are the units of evolution is due to Charles
Darwin and Alfred Wallace. It is striking that they could develop their theory of evolution without knowledge of genetics. Besides populations being subjective aggregates of living beings, in the biotic evolution objective aggregates play
a part. These objective aggregates consist of genes. Six years after Darwin’s publication of The origin of species (1859), Gregor Mendel discovered the laws of heredity. These remained unnoticed until 1900, and only some time later they turned
out to be the necessary supplements to the laws for populations.
Some populations reproduce only or mostly asexually (5.7). In section 5.6, I restrict myself to populations forming a
reproductive community, a set of organisms reproducing sexually. Within and through a population, genes are transported, increasing and decreasing in number.
a. The genetic identity of each living being is laid down in its genome, the ordered set of genes (5.2). The genes do not operate independent of each other. Usually, a combination of genes determines a characteristic
of the organism. In different phases of development, combinations of genes are simultaneously switched on of off. The linear order of the genes is very important. The number of genes is different in different species and may be very large. They are grouped
into a relatively small number of chromosomes, each chromosome corresponding to a DNA molecule. The human genome consists of 23 chromosome pairs and about 30,000 genes. The genes take only 5% of the human DNA, the rest is non-coding ‘junk-DNA’,
which function was not very clear at the end of the twentieth century. A prokaryote cell has only one chromosome.
In eukaryotes, genes occur in the cell nucleus as well as in several organelles, such as the mitochondria. The organelles are considered encapsulated prokaryotes (5.4).
Genes are not
subjectively living individuals like organisms, organs, tissues, cells, or even organelles. They have an
objective function in the character of a living cell. A genome should not be identified with the DNA molecules forming its material basis, neither a gene with a sequence of bases.
Confusion arises from using the same word for a sequence of nucleotides in a DNA molecule and its character, the pattern. In all cells of a plant the DNA molecules have the same pattern, the same character, which is called the plant’s genome. Likewise,
a gene is not a sequence of nucleotides, nor a particle in a physical or chemical sense, but a pattern of design. The same gene, the same pattern can be found at different positions in a genome, and at the same locus one finds in all cells of a plant the same
pair of genes. Each gene is the design for a polypeptide, and the genome is the design of the organism.
The biotic character of the genome is interlaced with the chemical character of
DNA molecules. The genome or genotype determines the organism’s hereditary constitution. The phenotype is developed according to the design expressed in the genome. Both phenotype and genotype refer to the same individual organism.
Nevertheless, genes have their own objective individuality. In asexual cell division, the genome remains the same. The parent cell transfers its genetic individuality to the daughter cells. In
sexual reproduction, objective individual genes are exchanged and a new subjective individual organism emerges.
b. A population is characterized by the possibility to exchange genes and is therefore the carrier of a gene pool. Although the members of the population belong to the same species, they are genetically differentiated. In a diploid cell, a
DNA molecule consists of a double helix. At each position or locus there are two genes. These genes may be identical (homozygote) or different (heterozygote). Different genes that can occupy the same locus in different organisms in a population are called
alleles. Some alleles dominate others. The distribution of the alleles over a population determines their genetic variation, satisfying Gregor Mendel’s laws in simple cases. In sexual reproduction, the pairs of genes separate, in order to form
new combinations in the new cell (5.3).
At any time, the gene pool is the collection of all genes present in the population. The exchange of alleles in sexual reproduction leads to changes
in the frequencies within the gene pool, but does not change the genes themselves. For change, several other mechanisms are known, such as mutation, crossing-over, and polyploidy.
Usually, the location of the genes does not change. It is a specific property of the species. Hence, the way genes co-operate is also specific for a species.
A population in which sexual
reproduction occurs without constraints is subject to the statistical law of Godfrey Hardy and Wilhelm Weinberg (1908): on a certain locus in the genome the frequency of the alleles in the gene pool in a stable population is constant, generation after generation.
Only selective factors and hybridization with another population may disturb the equilibrium. Hybridization
between related species or different populations of the same species give rise to a new species or race if three conditions are met. First, the hybrids are fertile. Second, there is a niche available in which the hybrids are better adapted than the original
population. Third, the new combination of genes becomes isolated and sufficiently stabilized to survive.
Observe that the organisms determine the frequency of the genes in the pool. The character of each gene is realized in DNA. Still, it makes no sense to count the number of DNA molecules in a population,
because DNA is found in each cell and most cells have no significance for the gene pool. Even the number of gametes is irrelevant for calculating the gene frequency. The frequency of genes in the pool is the weighed frequency of the organisms in the
population, being the carriers of the gene concerned. For instance, if at a certain locus a gene occurs
once in 10% of the organisms and twice in 10%, the gene has a frequency of 15% in the gene pool, because each locus contains two alleles.
By natural selection, the frequency of a gene may increase or decrease, depending on the fitness of the organisms in the population.
c. Because of external circumstances, the gene pool may change very fast. Within a few generations, the distribution of a gene pair AB may change from 90% A, 10% B into 10% A, 90% B.
This means that a population is able to adapt itself to changes in its habitat, and to increase its chances of survival and reproduction. In a radical environmental change (in particular if a part of the population is isolated), hereditary variation within
a species may give rise to the realization of a new species. Hence, adaptation and survival as concepts in the theory of evolution do not concern individual organisms (being genetically stable), but populations. Only populations are capable of genetic change.
Natural selection as such is not a random process,
but it is based on at least two random processes, to wit mutation and sexual reproduction. Which alleles combine in mating rests on chance. The enormous amounts of cells involved in reproduction compensate for the relatively small chance of progress.
e. The phenotype (not the genotype) determines the chance of survival of an organism in its environment. The phenotype is the coherent set of the functions
of all parts of the organism, its morphology, physiology, and its ability to reproduce. The genotype generates the phenotype, whereby development and environment factors play an additional but important part. Natural selection advances some phenotypes at the
cost of others, leading to changes in the gene pool. Together with changes in the genes themselves, natural selection induces small changes in each generation to accumulate to large changes after a large number of generations.
The received theory of evolution emerged shortly after 1930 from a merger of Charles Darwin’s theory of natural selection with genetics and molecular biology. It presupposes that evolution occurs in small steps.
Major changes consist of a sequence of small changes. In many cases, this is an acceptable theory. Nevertheless, it would be honest to admit that there is no biological explanation available for the emergence of prokaryotes (about three billion years ago);
of eukaryotes (circa one billion years ago); of multicellular organisms (in the Cambrium, circa 550 million years ago); of sexual reproduction; of animals; and of the main animal phyla, plant divisions, classes, and orders. At the end of the twentieth century,
the empirical evidence available from fossils and DNA sequencing is not sufficient to arrive at theories withstanding scientific critique.
5.7. Does a species correspond with
A natural character is defined as a set of laws determining an ensemble of possibilities besides a class of individuals. A class
and an ensemble are not restricted in number, space, and time. They do not change in the course of time and do not differ at different places. A population is not a class but a collection. Hence, it does not correspond to a character. The question of whether
a species corresponds to a character is more difficult to answer. ‘There is probably no other concept in biology that has remained so consistently controversial as the species concept.’
Philosophers interpreting the concept of a natural kind in an essentialist way rightly observe that a biotic species does not conform to that concept. However, the idea that a character is not an essence but a set of laws sheds a different light on the concept
of a species. The main problem appears to be that insufficient knowledge is available of the laws determining species. Instead, one investigates the much better accessible subject and object side of these unknown laws.
Generally speaking, biologists are realists, because they consider a species to be a natural set. Each living being belongs to a species, classified according to a variety of practical criteria, which do not always yield identical
results. Besides, there are quite a few theoretical definitions of a species. The distinction between operational
criteria used in practice and theoretical definitions is not always sharp. Practice and theory are mutually dependent. However, not distinguishing them gives rise to many misunderstandings.
Criteria to distinguish species from each other are grouped into genealogical (or phylogenetic), structural, and ecological criteria. This corresponds more or less to a division according to primary,
secondary, and tertiary characteristics.
Species can be distinguished because they show distinctive, specific properties. These are regular, therefore lawlike. This is not merely interesting
for biologists. In particular in sexual relationships, animals are able to distinguish other living beings from those of their own kind.
Primary criteria to distinguish species are genealogical. The biological taxonomy is based on empirical or theoretically established lineages. A population is a segment of a lineage. A taxon (for instance, a species, genus, family,
order, or phylum) is defined as a set of organisms having a common ancestry. A monophyletic taxon or clade comprises all and only organisms having a common ancestry. Birds and crocodiles are monophyletic, both apart and together. A set of organisms lacking
a common ancestry is called polyphyletic. Such a set, like that of all winged animals, is not suited for taxonomy. A taxon consisting of some but not all descendants of a common ancestor is called paraphyletic. For instance, reptiles have a common ancestry,
but they share it with the birds, which are not reptiles. Opinions differ about the usefulness of paraphyletic taxons.
The biological taxonomy clearly presupposes genetic relations
to constitute a general biotic relation frame. Descent providing the primary, genealogical criterion for
a species has two important consequences.
The first consequence is seldom explicitly mentioned, but always accepted. It is the assumption that an individual living being belongs to the
same species throughout its life. (It may change of population, e.g., by migration.) This means that species characteristics cannot be exclusively morphological. In particular the shape of multicellular fungi, plants, and animals changes dramatically during
various phases of life. The metamorphosis of a caterpillar into a butterfly is by no means an exception. The application of similarities and differences in taxonomy has to take into account the various phases of life of developing individuals.
Second, as a rule each living being belongs to the same species as its direct descendants and parents. Therefore the dimorphism of male and female specimens does not lead to a classification into
different species. A very rare exception to this rule occurs at the realization of a new species. A minimal theoretical definition says that a species necessarily corresponds to a lineage, starting at the moment it splits off from an earlier existing species,
and ending at its extinction.
this minimal definition would be sufficient as well as necessary, a species would be a collection, like a population bounded in number, space, and time. But this definition cannot be sufficient, because it leaves utterly unclear what the splitting of a species
means. Branching alone is not a sufficient criterion, because each lineage branches (an organism has various descendants, and in sexual replication each organism has two parents, four grandparents, etc.). According to the primary criterion alone, the assumption
that all organisms are genetically related would mean that either all organisms belong to the same species, or each sexual reproduction leads to a new species. Hence, additional secondary and perhaps tertiary criteria are needed to make clear, which kind of
branching leads to a new species.
The most practical criteria are structural. It concerns similarities and differences based on the DNA-structure (the genotype), besides the shape (morphology), and processes (physiology, development),
making up the phenotype. In DNA and RNA research, biologists look at similarities and differences with respect to various genes and their sequences, taking into account the locus where they occur. The comparison of genes at different loci does not always give
the same results. Hence people should be cautious with drawing conclusions. It should be observed that DNA and RNA research is usually only possible with respect to living or well-conserved cells and only establishes more or less contemporary relations. This also applies to other characteristics that cannot be fossilized, like behaviour. Non-contemporary similarities
and differences are mostly restricted to morphological ones. For the agreement between various related species, homologies are very important (5.6).
Many biologists accept as a decisive
distinction between species the existence of a reproductive gap between populations. Within a species, individuals
can mate fruitfully with each other, whereas individuals of different species cannot. This concerns a subject-subject relation.
According to this definition, horses and donkeys belong to different species. A horse and a donkey are able to mate, but their offspring, the mules, are not fertile. The mentioning of populations is relevant. The reproduction gap does not concern individuals
Sometimes, a population A belongs to the same species as population B, B ditto with C, but C does not with respect to A. Hence, the concept of a species according to this criterion is not always transitive. The possibility to mate
and having fertile descendants is only relevant for simultaneously living members of a population. Hence it serves as a secondary addition to the primary genealogical criterion, stating that organisms living long after each other (and therefore unable
to mate) may belong to the same species. Taking this into account, the mentioned lack of transitivity can be explained by assuming that one of the populations concerned is in the process of branching off. After some time, either A or C may
become to belong to an independent species.
The reproduction gap is in many cases a suitable criterion, but not always. First, some species only reproduce asexually. This is not an exception,
for they include the prokaryotes (the only organisms during three-quarters of the history of life on earth).
Second, many organisms that experts rank to different species are able to fertilize each other. Hybrid populations are more frequent in plants than in animals. The reproductive gap is in animals more pronounced than in plants, because of the animals’
mating behaviour and the corresponding sexual dimorphy.
A tertiary criterion concerns the disposition of a species to find a suitable niche or adaptive zone (5.5). How organisms adapt to their environment leads to the formulation of ecological criteria to distinguish species. This is a
relational criterion too, for adaptation does not only concern physical (e.g., climatic) circumstances, but in particular the competition with individuals of the same or of a different species.
Biologists and monist biophilosophers look after a universal concept of a species.
Supposing that a species corresponds to a character, it should be primarily biotically qualified. No difference of opinion is to be expected on that account. But what should be its secondary characteristic? Considering the analysis in section 5.4, for prokaryotes
the quantitative relation frame comes to mind (cell division); for unicellular or colonial eukaryotes the spatial frame (morphological shape and coherence); for differentiated plants the kinetic frame (physiology and development); finally, for sexually specialized
plants and animals the physical relation frame (the reproductive gap). A species can only be a universal biotic character if the concept of a species is differentiated with respect to secondary and tertiary characteristics. For instance, the secondary criterion
based on the reproductive gap is only applicable to sexually reproducing organisms. The pluralistic concept of a species finds its origin in the fact that all secondary and tertiary criteria are restrictively applicable, whereas the universal primary criterion
is necessary but not sufficient.
Some philosophers assume that species are comparable with organisms and they consider a species to be a biotic individual.
A species comes into being by branching off from another species, and it decays at extinction. Species change during their existence. It is true that these processes depend entirely on the replication of the organisms that are part of the species, but that
applies to multicellular organisms as well, whose development and growth depend on the reproduction of their cells.
Organisms belonging more or less simultaneously to the same species
form a population. Usually a population is a geographically isolated subset of a lineage, a set of organisms having the same ancestry. Both populations and lineages are temporal collections of individuals, not timeless classes. They are aggregates
as well, because their members are genetically related. However, an aggregate is not always an individual, and it is always a set of individuals. If considered as a lineage or population (or a set of populations), a species is a temporal collection of individual
organisms, subject to biotic laws. I shall not contest this vision that stresses the subject side of a species. But it does not answer the question of whether a species has a law side as well, corresponding with a character.
Both lineages and populations are products of a biotic dynamic evolution. Natural selection, genetic drift, and ecological circumstances
explain how lineages emerge, change, and disappear. Geographic isolation explains the existence of various populations belonging to the same species. But natural selection, genetic drift, or geographic isolation does not explain why a group
of living beings is viable in the circumstances constituting an adaptive zone. Unavoidably, such an explanation takes its starting point from law statements, whether hypothetical or confirmed. These propositions may very well include the supposition that a
lineage and its populations are spatio-temporal subsets of a timeless class, without violating the received facts and theories of evolution and genetics. The character of this class determines an ensemble of possibilities, partly realized in the individual
variation occurring in a population.
No more than species, the chemical elements have been realized from the beginning of the universe. Only after the universe was cooled down sufficiently, protons and electrons could form hydrogen and helium. Only after the formation of stars, hydrogen
and helium nuclei fused to become heavier nuclei. Nuclear physics provides a quite reliable picture of this chemical evolution. Doubtless, each isotope satisfies a set of laws constituting a character. I believe that the same applies to biotic species, although
the complexity of organisms makes it far more difficult to state in any detail which laws constitute a biotic character.
The crossing of a barrier between two species has an analogy in the well-known phenomenon of tunneling in quantum physics. An energy barrier usually separates a radioactive nucleus from
a more stable nucleus. This barrier is higher than the energy available to cross it. According to classical mechanics, a nucleus could never cross such a barrier, but quantum physics proves that there is a finite (even if small) probability that the nucleus
overtakes the barrier, like a car passes a mountain through a tunnel. A similar event occurs in the formation of molecules in a chemical reaction. In this case, the possibility to overtake the energy barrier depends on external circumstances like the temperature.
The presence of a catalyst may lower the energy barrier. In biochemical processes enzymes have a comparable function. The possibility that an individual physical or chemical thing changes of character is therefore a fact, both theoretically and experimentally
established. Moreover, in all chemical reactions molecules change of character, dependent on circumstances like temperature.
Similarly, at the realization of a new species, circumstances
like climate changes may enhance or diminish the probability of overcoming one or more constraints. A small, geographically isolated population will do that easier than a large, widely dispersed population. Since 1972, biology knows the theory of ‘punctuated
equilibrium’. From paleontological sources, Niles Eldredge and Stephen Gould derived that in a relatively short time (compared to much longer periods of stable equilibrium), a major transition from one species to another may occur.
Quantum physics explains the transition from one character to the other by tunneling, but tunneling does not explain the existence of the characters concerned. Natural selection
explains why constraints can be overcome, not why there are constraints, or which types of constraints are operative. Natural selection explains changes within species and from one species to the other, but not why there are species, and which species exist.
On the contrary, the existence of species is a condition for the action of natural selection. Populations change within a species, and sometimes they migrate from one species to another one, and its motor, its dynamic force, is natural selection. However,
natural selection does not explain everything. The success of natural selection is only explicable by assuming that a population after adaptation is in a more stable equilibrium with its environment than before. What is stable or better adapted, why the chances
of survival of an organism increase by a change induced by natural selection, cannot be explained by natural selection itself. Natural selection explains why a population changes its gene pool, but it does not explain why the new situation is more viable.
To explain this requires research into the circumstances in which the populations live and into the characters that determine the species.
On the one side, the standard theories about
evolution, genetics, ecology, and molecular biology do not exclude the possibility that each species corresponds to a character, a set of laws defining an ensemble of possibilities, sometimes (and never exhaustively) realized by a population of organisms.
After all, ‘by far the commonest fate of every species is either to persist through time without evolving further or to become extinct.’
On the other hand, it cannot be proved that a species corresponds to a character. That would only be empirically demonstrable. The idea that an empirical species is a subset of a class subject
to a specific set of laws can only be confirmed by pointing out such laws. For instance, both genetics and
development biology look for lawful conditions concerning the constitution of genes and chromosomes determining the phenotype of a viable organism belonging to a species. That is because the biotic expression of a character is a natural design, the genome,
objectively laid down in the species-specific DNA.
Natural selection may be considered a random push for the dynamic development of populations of living beings. This development also
requires the specific lawful pull of the species concerned.
Should we not consider the ascription of
an unchangeable and lawful character to species a relapse into essentialism? Essentialism is a theory ascribing
a priori an autonomous existence to plants, animals, and other organisms. Their essence is established on rational grounds, preceding empirical experience. Essentialism presupposes the possibility to formulate necessary and sufficient conditions for
the existence of each species. The conditions for any species should be independent of the conditions for any other species.
This view differs widely from the idea of a character being a specific set of laws. With respect to the subject side, as far as essentialism excludes evolution, the theory of characters is by no means essentialist.
According to Aristotelian essentialism, each species would be autonomous. Biologists and philosophers seem to assume that this paradigm is still applicable to physics and chemistry. But physical things can only exist in interaction
with other things, and the actual realization of physically qualified characters is only possible if circumstances permit. For instance, in the centre of the sun no molecules can exist, but we can only say that assuming that the laws which determine the possible
existence of molecules are valid within the sun as much as elsewhere. The astrophysical and chemical theories of evolution assume that physical things emerged gradually, analogous to organisms in the biotic evolution. Nevertheless, it is generally accepted
that particles, atoms, molecules, and crystals are subject to laws that are everywhere and always valid.
Physical and chemical things can only exist in interaction with each other in
suitable circumstances. Similarly, living organisms can only exist in genetic relations with other organisms, permitting the circumstances. Each living organism would perish in absence of other living beings, and no organism can survive in an environment that
does not provide a suitable niche.
My reasons to consider a species to be a character are a posteriori, based on scientific arguments open to empirical research. It is a hypothesis,
like any other scientific assumption open to discussion. And it is a hypothesis leaving room for the evolution of a population within a species as well as from one species to another one. It is a hypothesis fully acknowledging Darwin’s great discovery
of natural selection. Moreover, this hypothesis recognizes the importance of environmental circumstances both determining possibilities and their realization. The laws are not the only conditions for existence. Physical and ecological circumstances are conditions
as well. The realization of species can only occur in a certain order, with relatively small transitions. In this respect, too, the evolution of species does not differ from the evolution of chemical elements.
Although essentialists are able to take circumstances into account, the theory of characters moves ahead. The possibilities offered by a character are not merely realizable if the circumstances permit, but the ecological laws are partly
the same as the laws constituting the character of a species. The laws forming a character for one species are not separated from the laws forming the character of another species, or from the laws determining biotic processes. Essentialism supposes that each
species can be defined independent of any other species.
It is undeniable that my hypothesis runs counter to the kind of evolutionism that denies the existence of constant laws. From
the above discussion it will be clear that I do not criticize Charles Darwin’s theory and its synthesis with genetics and molecular biology. By natural selection, the theory of evolution explains the actual dynamic process of becoming and the
evolution of populations. I believe that this theory does not contradict the view that species correspond to unchangeable characters and their ensembles. On the contrary, I believe that the facts corroborate the proposed model better than a radical evolutionism
denying the existence of laws. The hypothesis that unchangeable laws dominate the species can be investigated on empirical grounds. This discussion belongs to the competence of empirical science.
The answer to the question of whether a species corresponds to a character does not depend on the acceptance or rejection of the belief that characters – not only biotic species – consist of laws given by God. The empirical approach that
I advocate is at variance with the creationist view assuming a priori that the species are unchangeable, rejecting any theory of evolution. Creationism uses the bible as a source of scientific knowledge preceding and superseding scientific
research. It contradicts the view that the problem of whether species correspond to constant characters can only be solved a posteriori, based on scientific research.
For the time being, I am inclined to conclude that a species at the law side corresponds with a biotically qualified character, an unchangeable set of laws. The least one can say is that the recognition
of a species or a higher taxonomical unit requires an insight into the regularities which make an organism to belong to that category. At the subject side, a species is realized by a lineage, an aggregate of individual organisms, hence with a collection,
bounded in number, space, and time.
Evolution means the subjective realization of species. Natural selection is its motor and explains how species are realized. Whether a species
is realizable at a certain place and time depends on the character of the species; on the preceding realization of a related species (on which natural selection acts); on the presence of other species (the ecological environment); and on physical
circumstances like the climate (the physical environment).
I have no intention to suggest that the biotic evolution is comparable to the astrophysical and chemical evolution in all respects.
I conceive of each evolution as a realization of possibilities and dispositions. But the way by which this occurs is strongly different. For physical and chemical things and events, interaction is decisive, including circumstances like temperature and the
availability of matter and energy. The biotic evolution depends on sexual and asexual reproduction, with the possibility of variation and natural selection.
Another difference concerns
the reproducibility of evolution. The physical evolution of the chemical elements and of molecules repeats itself in each star and each stellar system. In contrast, it is often stated that the biotic evolution is unique and cannot be repeated. It may be better
to assert that the actual course of the biotic evolution is far more improbable than that of the physical and chemical ones. Comparable circumstances – a condition for recapitulation – never or hardly ever occur in living nature. In particle accelerators
the astrophysical evolution is copied, the chemical industry produces artificial materials, agriculture improves races, in laboratories new species are cultivated, and the bio-industry manipulates genes. All this would be difficult to explain if one loses
sight of the distinction between law and subject.
As a character, a biotic design is a set of laws, but
for a scientist this does no longer imply a divine designer. Whereas this does not solve the question of
the origin of the natural laws, natural science became liberated from too naive views about the observability of divine interventions in empirical reality.
Essentialism survived longest
in the plant and animal taxonomy. Until the middle of the twentieth century, this considered the system of species, genera, families, classes, orders, and phyla or divisions to be a logical classification. In this classification, each category was characterized
by one or more essential properties. Biological essentialism was not a remains of the Middle Ages, but a
fruit of the Renaissance. From John Ray to Carl Linnaeus, many realistic naturists accepted the existence of unchangeable species, besides biologists having a nominalist view of species.
The difficulty that some philosophers have with the modern concept of a species can be reduced to a conscious or subconscious allegiance to an essentialist view. The difficulty that some biologists
have with the idea of natural law is their abhorrence of essentialism. Therefore, it is important to distinguish
essence from lawfulness. The ‘essential’ (necessary and sufficient) properties do not determine a character. Rather, the laws constituting a character determine the objective properties of the things or processes concerned.
These properties, represented in an ensemble, may display such a large statistical variation that necessary and sufficient properties are hard to find.
Moreover, the laws and properties do not determine essences but relations.
A second reason why some biologists are wary of the idea of natural law is that they (like many philosophers)
have a physicalist view of laws. Rightly, they observe that the physical and chemical model of a natural law is not applicable to biology.
The theory of evolution is considered a narrative about the history of life, rather than a theory about processes governed by natural laws.
However, biologists will probably not deny that their work consists of finding order in living nature. The
theory of evolution would not exist without the supposition that the laws for life, that are now empirically discovered, held millions of years ago as well. The question of whether other planets host living organisms can only arise if it is assumed that these
laws hold there, too.
reason may be the assumption that a law only deserves the status of natural law, if it holds universally and is expressible in a mathematical formula. A mathematical formulation may enlarge the scope of a law statement. Yet the idea of natural law does not
imply that it has necessarily a mathematical form. Neither should a law apply to all physical things, plants, and animals. Every regularity, every recurrent design or pattern, and every invariant property is to be considered lawful. In particular each character
expresses its own specific law conformity. In the theory of evolution biologists apply whatever patterns they discover in the present to events in the past. Hence they implicitly acknowledge the persistence of natural laws, also in the field of biology.
Anyhow, Charles Darwin was not wary of natural laws. At the end of his On the origin of species he wrote:
is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed
forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction;
Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the
Extinction of less-improved forms.’
Mayr 1982, 56: ‘Except for the twilight zone of the origin of life, the possession of a genetic program provides for an absolute difference between organisms and inanimate matter.’ Ibid. 629: ‘… the existence of a genetic program …
constitutes the most fundamental difference between living organisms and the world of inanimate objects, and there is no biological phenomenon in which the genetic program is not involved …’. Jacob 1970, 4: ‘Everything in a living being
is centered on reproduction’. Rensch 1968, 35: ‘… “life” is not so much defined by certain single characters but by their combination into individualized, purposefully functioning systems showing a specific activity, limited
to a certain life span, but capable of reproduction, and undergoing gradually hereditary alterations over long periods.’
This does not exclude neoteny and other forms of heterochrony, see Raff 1996, chapter 8.
Farley 1974; Bowler 1989.
Monod 1970, 102-103: ‘… from the bacterium to man the chemical machinery is essentially the same … 1. In its structure: all living beings … are made up of … proteins and nucleic acids … constituted by the assembling
of the same residues … 2. In its functioning: the same reactions, or rather sequences of reactions, are used in all organisms for the essential chemical operations …’
 Rosenberg 1985, 136-152.
 At the end of the nineteenth century, energeticists like Wilhelm Ostwald assumed that thermodynamics
should be able to explain all physical and chemical processes. Atomic theory and quantum physics made clear that thermodynamics is too general for that. Likewise, in my view, evolution theory is not specific enough to explain biotic characters.
 According to Rosenberg 1985,
137-138, ‘biological entity’, ‘parent of’ and ‘ancestor’ are primitive, undefinable concepts in the following two axioms: ‘No biological entity is a parent of itself. If a is an ancestor of b, then
b is not an ancestor of a.’ If the mentioned terms are undefined, the natural numbers satisfy these axioms as well.
Panchen 1992, chapter 9.
Dawkins 1983, 16: ‘If you find something, anywhere in the universe, whose structure is complex and gives the strong appearance of having been designed for a purpose, then that something either is alive, or was once alive, or is an artefact created by
something alive.’ Kitcher 1993, 270: ‘Entities have functions when they are designed to do something, and their function is what they are designed to do. Design can stem from the intentions of a cognitive agent or from the operation of selection
In RNA, uracil (U) replaces thymine. The production of uracil costs less energy than that of thymine, which is more stable, see Rosenberg 1985, 38-43. Stability is for DNA more important than for RNA that is assembled repeatedly. Hence, mistakes in the transfer
of design are easy to correct. The double helix structure also enhances the stability of DNA. RNA consists of only one series of nucleotides.
A protein is a large polypeptide. Sometimes the same gene assembles more than one protein. Often a gene occurs more than once in the DNA, its locus determining how the gene co-operates with other genes. Hence, similar genes may have different functions. A
direct relation between a gene and a phenotypic characteristic is rare. See Hull 1974, 15-19.
According to the ‘central dogma of molecular biology’, formulated by Francis Crick, the transfer of information from DNA via RNA (‘transcription’ by mRNA) to the polypeptides (‘translation’ by tRNA) is irreversible. With
respect to the first step, the dogma does not apply entirely to viruses, and there are important differences between prokaryotes and eukaryotes. The intervention of RNA is necessary in eukaryotes, because DNA is positioned in the cell nucleus, whereas the
assembly of the polypeptides occurs elsewhere (in ribosomes). In prokaryotes, the translation may start before the transcription is finished. In transcription, a third form is produced, rRNA, concentrated in the ribosome, the organelle where the assembly of
polypeptides takes place. Because RNA has mostly a transport function, its tertiary characteristic may be called kinetic.
Epigenesis is the name of the process, in which each phase in the development of a plant or animal is determined by preceding phases, genes and environment, see McFarland 1999, 27-29.
 Dawkins 1986, 295-296; McFarland 1999, 27. The conception of the composition
of DNA as a code is a metaphor, inspired by the discovery that the structure of DNA can be written in only four symbols.
Raff 1996, chapter 10. Ibid. 27: ‘If each new species required the reinvention of control elements, there would not be time enough for much evolution at all, let alone the spectacularly rapid evolution of novel features observed in the phylogenetic record.
There is a kind of tinkering at work, in which the same regulatory elements are recombined into new developmental machines. Evolution requires the dissociability of developmental processes. Dissociability of processes requires the dissociability of molecular
components and their reassembly.’
Osmosis occurs if a membrane lets pass a solvent (usually water) but not the solved matter. The solvent moves through the membrane in the direction of the highest concentration of the solved matter. This induces a pressure difference across the membrane that
counteracts the transport. In equilibrium, the osmotic pressure in some desert plants can be up to a hundred times the atmospheric pressure.
In haploid cells, the cell nucleus contains a single string of chromosomes, in diploid cells the chromosomes are paired. Each diploid gene occurs in a pair, except the sex chromosomes, being different in males (XY), equal in females (XX).
Each chromosome is a single DNA molecule and consists of a large number of genes. The position of the genes on a chromosome is of decisive significance. On each position (locus) in a chromosome pair, there is at most one pair of genes, being homozygote
(equal) or heterozygote (unequal). If in different individuals different genes can occupy the same locus, these genes are called alleles.
Griffiths, Gray 1994.
Griffiths, Gray 1994.
During the twentieth century, the attention of biologists was so much directed to evolution and natural selection, that the investigation of individual development processes (in which natural selection does not play a part) receded to the background. The complexity
of these processes yields an alternative or additional explanation for the fact that relatively little is known about them. Some creationists take for granted ‘natural’ processes in the development of a human being from its conception, during and
after pregnancy, while considering similar processes incomprehensible in evolution. A standard objection is that one cannot understand how by natural selection such a complicated organ like the human eye could evolve even in five hundred million years. However,
who can explain the development of the human eyesight in nine months, starting from a single fertilized cell? In both cases, biologists have a broad understanding of the process, without being able to explain all details. (I am not suggesting here that the
evolution and the development of the visual faculty are analogous processes.)
Mayr 1982, 140, 244; Margulis, Schwartz 1982, 5-11; Ruse 1982, 169-171.
These organelles are about as large as prokaryotic cells. RNA research indicates that mitochondria are genetically related to the purple group and chloroplasts to the cyanobacteria, both belonging to the eubacteria. The most primitive eukaryotes, the archaezoa,
do not contain mitochondria of other organelles besides their nucleus. The similarity between prokaryotes and the organelles in eukaryotic cells was first pointed out by Lynn Margulis, in 1965.
 Contrary to bacteria, viruses are not capable of independently assembling DNA,
RNA and polypeptides, and they can only reproduce parasitically in a cell. Some viruses can be isolated forming a substance that is only physically and chemically active. Only if a virus enters a cell, it comes to life and starts reproducing. Outside the cell,
a virus is primarily physically qualified, having a biotic disposition, to be actualized within a cell. Because a virus mainly transports DNA, its character may be considered to have a (tertiary) kinetic disposition (like RNA). A virus has a characteristic
shape differing from the shape of a cell.
Likewise, an atomic nuleus (having a spatially founded character) acts like a quantitative unit in the character of an atom.
Margulis, Schwartz 1982. Up till the sixties, besides the animal kingdom only one kingdom of plants was recognized, including the monera, protista and fungi besides the ‘true’ plants, see Greulach, Adams 1962, 28.
 Hence, a population is not a class but a collection. It
is a spatial cross section of a lineage, which in turn is a temporally extended population, see de Queiroz 1999, 53-54. Besides being genetically homogeneous, a population is also genetically varied, see below.
 Darwin 1859, chapter 3.
 Purves et al. 1998, chapter 28: ‘Fungi: A kingdom
‘Survival of the fittest’ is sometimes called circular, see e.g. Popper 1974, 137; Dampier 1929, 319: ‘That which is fit survives, and that which survives is fit’. According to Rosenberg 1985, chapter 6 this circularity is caused by
the fact that fitness is a primitive, undefinable concept in the theory of evolution. Fitness is not definable, but it is measurable as reproductive success. See also Sober 1993, 69-73. According to McFarland 1999, 78, this circularity is removed by relating
survival to an individual and fitness to its offspring: ‘the fit are those who fit their existing environments and whose descendants will fit future environments … in defining fitness, we are looking for a quantity that will reflect the probability
that, after a given lapse of time, the animal will have left descendants’. Fitness is a quantitatively founded magnitude, lacking a metric. Fitness depends on the reproduction of an individual, and on that of its next of kin. This is called ‘inclusive
fitness’, explaining the ‘altruistic’ behaviour of bees, for instance.
Darwin 1859, chapter 4.
Panchen 1992, chapter 4.
Mayr 1982, 611; Raff 1996, 375-382.
 Dawkins 1976 assumes that the ‘selfish genes’ are the subjects
to evolution. But according to Mayr 2000, 68-69: ‘The geneticists, almost from 1900 on, in a rather reductionist spirit preferred to consider the gene the target of evolution. In the past 25 years, however, they have largely returned to the Darwinian
view that the individual is the principal target.’ See also Sober 1993, chapter 4.
Mayr 1982, 62: ‘The claim that genetics has been reduced to chemistry after the discovery of DNA, RNA, and certain enzymes cannot be justified … The essential concepts of genetics, like gene, genotype … are not chemical concepts at all
Ruse 1982, 21, 30, 200-207.
Mutations may have a physical cause (e.g., radioactivity), or a biotic one (e.g., a virus). Mutations are usually indifferent or even lethal, but sometimes enriching. For every gene, they are very rare, but because there are many genes in an individual and
even more in a gene pool, they contribute significantly to the variation within a species. Crossing-over means a regrouping of genes over the chromosomes. Polyploidy means that a DNA molecule consists of more than two strings, on each or some loci there are
three genes in stead of two.
Hull 1974, 57-58; Ridley 1993, 87-92, 131-132. Populations are hardly ever in equilibrium. The relevance of the law of Hardy and Weinberg is that deviations point to equilibrium disturbing factors. In small populations ‘genetic drift’ occurs, changes
in the gene pool caused by accidental circumstances.
Ridley 1993, 42-43. Usually, hybridization is impossible, because the offspring is not viable, or because the offspring is not fertile, or because the offspring has a decreasing fertility in later generations.
 Ridley 1993, 387: ‘A community of interbreeding organisms is,
in population genetic terms, a gene pool.’
The complication that on different loci the same gene may occur is left out of consideration in this example.
Dawkins 1986, 43, 62.
Mayr 1982, 251. On the biological species concept, see Mayr 1982, chapter 6; Rosenberg 1985, chapter 7; Ereshefsky 1992; Ridley 1993, chapter 15; Wilson (ed.) 1999.
 Panchen 1992, 337-338 mentions seven species concepts, others count more than twenty, see Hull 1999.
 See de Queiroz, 1999, 64:
‘… the species problem results from confusing the concept of a species itself with the operations and evidence that are used to put that concept in practice.’
 de Queiroz 1999, 77: ‘… the general lineage concept is a quintessential biological
species concept: inanimate objects don’t form lineages.’
de Queiroz 1999; Mishler, Brandon, 1987, 310.
Ereshefsky 1992, 350; de Queiroz 1999, 60, 63: ‘In effect, the alternative species definitions are conjunctive definitions. All definitions have a common primary necessary property – being a segment of a population-level lineage – but each
has a different secondary property – reproductive isolation, occupation of a distinct adaptive zone, monophyly, and so on.’
For some fossils DNA research is possible. An exceptional record concerns a fossil aged 135 millions years.
Mayr 1982, 273: ‘A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.’ Mayr, ibid. 272 mentions three aspects of a biotic species. ‘The first is to envision species
not as types but as populations (or groups of populations), that is, to shift from essentialism to population thinking. The second is to define species not in terms of degree of difference but by distinctness, that is, by the reproductive gap. And third, to
define species not by intrinsic properties but by their relation to other co-existing species, a relation expressed both behaviorally (noninterbreeding) and ecologically (not fatally competing).’
 Mayr 1982, 286: ‘The word “species”… designates a
Mating behaviour leads to the ‘recognition species concept’, see Ridley 1993, 392-393.
According to Hull 1999, 38-39, the concept of a species ought to be universal (applicable to all organisms), practical in use, and theoretically significant. Hull, ibid. 25, observes that monists are usually realists, pluralists being nominalists.
 Dupré 1999. Likewise,
the physical concept of natural kinds is not universal. For quantitatively, spatially, and kinetically founded characters, different secondary criteria apply.
 Rosenberg 1985, 204-212; Ridley 1993, 403-404. Hull 1999, 32: ‘when species are supposed to be the things
that evolve, they fit more naturally in the category individual (or historical entity) than the category class (or kind).’ Hull assumes a duality: ‘Classes are spatio-temporally unrestricted, whereas individuals are spatio-temporally
localized and connected. Given this fairly traditional distinction, we argued that species are more like individuals than classes’ (32-33). Clearly, Hull does not distinguish between aggregates and individuals. For a criticism, see Mishler, Brandon,
1987; de Queiroz, Donoghue, 1988; Sober 1993, 149-159; de Queiroz 1999, 67-68.
Boyd 1999, 141 identifies ‘… a class of natural kinds, properties and relations whose definitions are provided not by any set of necessary and sufficient conditions, but instead by a “homeostatically” sustained clustering of those
properties or relations. It is a feature of such homeostatic property cluster (HPC) kinds (…) that there is always some indeterminacy or “vagueness” in their extensions.’
 Based on an essentialist interpretation, Mayr 1982, 251 turns down
the analogy of the species concept in biology with that of mineralogy or chemistry: ‘For a species name in mineralogy is on the whole a class name, defined in terms of a set of properties essential for membership in the class.’
 According to Stebbins 1982, 16-21
such a transition takes 50,000 years or more, whereas a stable period may last millions of years. See Gould, Vrba 1982; Ridley 1993, chapter 19; Strauss 2009, 487-496..
 Evolutionists have a tendency to deny the existence of biotic laws, see e.g. Dawkins 1986, 10-15. Nevertheless,
Griffiths 1999 asserts that there are laws valid for taxonomy. Ruse 1973, 24-31 stresses that biology needs laws no less than the inorganic sciences. He mentions Mendel’s laws as an example. And Ereshefsky 1992, 360, observes at least that ‘…
there may be universal generalizations whose predicates are the names of types of basal taxonomic units … So though no laws exist about particular species taxa, there may very well be laws about types of species taxa.’.
 Toulmin, Goodfield 1965. Mayr 1982,
175-177 observes that in Carl Linnaeus’ taxonomy the genera are defined in an essentialist way. Mayr, ibid. 176 quotes from Linnaeus’ Philosophia Botanica (1751): ‘The ‘character’ is the definition of the genus, it is
threefold: the factitious, the essential, and the natural. The generic character is the same as the definition of the genus … The essential definition attributes to the genus to which it applies
a characteristic which is very particularly restricted to it, and which is special. The essential definition [character] distinguishes, by means of a unique idea, each genus from its neighbors in the same natural order.’
 Sober 1993, 145-149; Hull 1999, 33; Wilson 1999, 188.
 Dawkins 1986, chapter 1.
 See e.g. Mayr 1982, 260:
‘The essentialist species concept … postulated four species characteristics: (1) species consist of similar individuals sharing in the same essence; (2) each species is separated from all others by a sharp discontinuity; (3) each species is constant
through time; and (4) there are severe limitations to the possible variation of any one species.’
Toulmin, Goodfield 1965, chapter 8; Panchen 1992, chapter 6. Ray and Linnaeus were more (Aristotelian) realist than (Platonic) idealist. Mayr 1982, 38, 87, 304-305 ascribes the influence of essentialism to Plato. ‘Without questioning the importance of
Plato for the history of philosophy, I must say that for biology he was a disaster.’ (ibid. 87). Mayr shows more respect for Aristotle, who indeed has done epoch-making work for biology (ibid. 87-91, 149-154). However, Aristotle was an essentialist no
less than Plato was.
Rosenberg 1985, 188: ‘Essentialism with respect to species is the claim that for each species there is a nontrivial set of properties of individual organisms that is central to and distinctive of them or even individually necessary and jointly sufficient
for membership in that species.’ The identification of a class by necessary and sufficient conditions is a remnant of rationalistic essentialism, see, e.g., Hull 1999, 33; Wilson 1999, 188. Boyd 1999, 141-142 calls his conception of a species as ‘…
a class of natural kinds, properties and relations whose definitions are provided not by any set of necessary and sufficient conditions, but instead by a “homeostatically” sustained clustering of those properties or relations’ a form of essentialism,
to be distinguished from the essentialism of Linnaeus etc. Griffiths 1999 contests the view that there are no natural laws (in the form of generalizations allowing of counterfactuals) concerning taxonomy. Definition of a natural kind by properties may have
a place in natural history, but not in a modern scientific analysis based on theories, in which laws dominate, not properties.
Hull 1974, 47; Rosenberg 1985, 190-191.
Hull 1974, 49; Mayr 1982, 37-43, 846. To the nineteenth-century physicalist idea of law belonged determinism and causality. However, determinism is past, and causality is no longer identified with law conformity but is considered a physical relation.
 Mayr 2000, 68: ‘Laws
and experiments are inappropriate techniques for the explication of such events. Instead, one constructs a historical narrative, consisting of a tentative construction of the particular scenario that led to the events one is trying to explain.’
 Rosenberg 1985, 122-126,
211, 219. ‘But biology is not characterized by the absence of laws; it has generalizations of the strength, universality, and scope of Newton’s laws: the principles of the theory of natural selection, for instance.’ (ibid. 211). About M.B.
Williams’ axiomatization of the theory of evolution, (ibid. 136-152, see also Hull 1974, 64-66), Rosenberg observes: ‘None of the axioms is expressed in terms that restrict it to any particular spatio-temporal region. If the theory is true, it
is true everywhere and always. If there ever were, or are now, or ever will be biological entities that satisfy the parent-of relation, anywhere in the universe, then they will evolve in accordance with this theory (or else the theory is false).’ (ibid.
152). But concerning the study of what is called in this book ‘characters’, Rosenberg believes that these ‘… are not to be expected to produce general laws that manifest the required universality, generality, and exceptionlessness.’
(ibid. 219). Yes indeed, it concerns specific laws. Evolutionists tend to deny the existence of biotic laws, see e.g. Dawkins 1986, 10-15. However, Ruse 1973, 24-31 stresses that biology is no less than the inorganic sciences in need of laws. He points to
Mendel’s laws for an example. Rensch 1968 gives a list of about one hundred biological generalizations. Griffiths 1999 asserts that there are laws valid for taxonomy. Ereshefsky 1992, 360, observes at least that ‘… there may be universal
generalizations whose predicates are the names of types of basal taxonomic units … So though no laws exist about particular species taxa, there may very well be laws about types of species taxa.’ For a discussion of the functioning of
laws in biology, see Hull 1974, chapter 3.