Chapter 14. CONCEPTS OF EVOLUTION
Our discussion of the ‘quasi-purposive’ in nature brings us to the topic of ‘evolution’, which some have claimed to be a case in point. Keeping an open mind, we shall examine the issue. Evolution primarily means change – progressive change over a long time such that the later appearances differ considerably from the earlier ones.
The term is sometimes used in physics, to describe the history of inanimate matter from primordial quarks through astronomical events to heavy atoms, organic molecules and finally (so far) to living cells. In biology, it is used to refer to changes of population groups (species), implying a more radical sort of change than the mere ‘development’ of individuals, which term refers to the growth of an organism (its organs becoming more formed and functional, cells dividing and multiplying, and so forth, making the whole more competent to deal with the demands and dangers of living).
Note that my interest here is not in fully detailing, and justifying or criticizing, any biological theory. I gather that there are difficulties in the subject, many of which have no doubt been resolved, and many perhaps not. I admit at the outset that I am not qualified to judge between the pros and cons. My approach is philosophical rather than biological. It could be considered an investigation (to my own satisfaction, as a logician) into the discourse relative to evolution – i.e. what is meant by the propositional form “X evolves to Y”; what sort of more basic causal propositions underlie it; what concepts does it appeal to.
Now, in my earlier work Future Logic, I dealt with the logic of change in some detail – with reference to two main forms of change:
· ‘Alteration’, where some individual thing classed as X and not Y to begin with, is classed as X and Y at a later time; for which I used the form “this X got to be Y”.
· ‘Mutation’, where some individual thing classed as X and not Y to begin with, is classed as Y and not X at a later time, for which I used the form “this X became Y”.
In the former case, the individual remains X while it changes from notY to Y; whereas in the latter case, the individual ceases to be X before it changes over to Y. Note that it is possible to rephrase alteration as mutation (this X-notY became X-Y), or mutation as alteration (this thing, that was X-notY, got to be Y-notX).
These forms are of course quantifiable, i.e. we can say ‘all X’ or ‘some X’ instead of ‘this X’. Such forms are useful to discussion of movements of individuals from one class to another, while remaining essentially the same in some respect or without remaining essentially the same. Needless to say, they ignore intermediate stages, but such complications can be dealt with by appropriate specifications. However, such forms are not applicable to evolution, though they may be used to discuss aspects or portions of it.
The word ‘mutation’, as here used (i.e. by the logician) seems to correspond to that intended by biologists in the expression ‘genetic mutation’. For the reader’s information, a ‘gene’ consists of a long chain of molecules with certain properties. Genes (singly or collectively), in conjunction with some environmental conditions, determine many of physical traits and processes, including many behavior patterns, of living beings. They are inherited from generation to generation since life began, ensuring that attributes of parents are reproduced in offspring, essentially unchanged.
Without getting too deeply into biochemistry, the essential molecular structure involved in genes is DNA, which consists of four nucleotides labeled A, C, G, T. The latter can only be physically paired in four ways TA, CG, AT, GC, which are respectively labeled U, C, A, G. The latter in turn constitute the four letters of genetic coding; these may be combined in 64 sets of three letters (called codons), i.e. UUU, UCA, GAU, CGA, etc. These triplets give rise to only 20 amino acids (and three other molecules that act as ‘stop signals’). A few hundred amino acids may combine in a repetitive series; for example, CAU-CAU-CAU-etc. That is the molecular structure of a gene.
The same gene may be said have two or more variants – if we now understand the term ‘gene’ with reference to the biological role it plays, rather than to its exact chemistry. For instance, the gene controlling the color of the flowers of a pea plant. Such variants are called ‘alleles’, and the molecular difference between them may be just one amino acid in a chain of several hundred. In our example, there is one allele for purple flowers (dominant) and another for white ones (recessive). When these genes are brought together in reproduction, they behave according to certain rules, giving rise to the numerous variations between the individuals of a species. Generally speaking, genes are stable and reproduce predictably.
However, very rarely (perhaps once in a thousand or a million), mutation occurs in genes, due to chance physical causatives, such as radiation or chemical pollution. Genetic mutation may consist of the substitution, deletion or addition of a single letter of genetic code, but this radically changes the nature and effect of the gene. For examples, in the series CAU-CAU-etc., if a U is deleted, we obtain CAU-CA↓C-AUC-AUC-etc.; alternatively, if a C is added, we obtain CAU-CCA-UCA-UCA-etc. Note how the CAU sequence is not lost, but shifted over by one. If the mutation occurs in sex cells or cells giving rise to them, the mutant gene is transmitted to eventual offspring (which may or not survive and in turn reproduce).
Thus, from a logical perspective, if we symbolize (these symbols are invented, not drawn from genetics) the original gene as O and the mutant gene as M, mutation is expressed in a proposition of the form “gene O becomes gene M”. If, alternatively, we consider O and M to be ‘the same’ gene K, in the sense that both refer to the genetic key to some specific biological trait or process (like flower color), without specifying the precise variation (e.g. blue or red color), then we can describe the change from O to M as alteration of K.
Another form important to biology is of course the form of reproduction, say: “X reproduces Y”, where the terms X and Y refer to similar individual entities. This form not only implies a change (i.e. at least, the arising of Y), but also signifies a causal relation between the terms (the first gives rise to the second, somehow). The individuals involved may be whole organisms – or they may be genes. In either case, the form might be applied to a parent and its immediate offspring, or more broadly to the offspring of its offspring, etc.
Note that I have, above, presumed genetic mutation to imply the form of logical mutation (as above defined), such that an individual gene (O) has itself physically become another individual gene (M). The mutant gene M might then go on and reproduce faithful copies of itself. But it would also be conceivable for the genes concerned (O and M) to be different individuals, the former giving rise to the latter by a faulty duplication process and the two coexisting for some time. In this alternative scenario, genetic mutation would not imply logical mutation, but a form of reproduction not implying physical continuity between the parent gene and its immediate offspring, a relation more akin to that between a parent and the offspring of its offspring. I do not know enough biology to say whether such ‘unlike reproduction’ ever actually occurs.
In the case of evolution, a distinct form “species X evolves to species Y” must be used, such that the individuals subsumed by the initial class X are not the same units as the individuals subsumed by the final class Y. Note well: the units of class Y are not and never were units of class X – so this is quite a different logical situation to alteration and mutation!
Here again, note, we only specify the starting and ending states, though there might be a long progression of changes (alterations and mutations) in between them. Yet, some sort of continuity is implied, some causal thread tying the initial and final units – in biology that is the fact of reproduction or affiliation: the former units are ancestors and the latter are their descendents. Furthermore, the causes of the changes involved are not specified or implied, but must be separately clarified using appropriate causal propositions. The chronology, or time between the terms, can also be separately specified.
In evolution, the individuals subsumed by a class procreate other individuals of the same class, but these are over time slightly altered or mutated; and at some point, the changes are so pronounced that we can no longer regard the new individuals as belonging to the same class. In evolution, one class (or a segment thereof) is effectively replaced by another, a bit as in ‘mutation’ an individual undergoes a change of essence. Thus, the form of evolution has aspects of both extensional and natural modality, in that it its terms do not refer to the same individuals and yet a real continuity between them is implied. As we shall see, this modal duality also occurs in other aspects of evolution.
The way of reference involved in this propositional form is thus neither distributive, nor collective, nor collectional (as in other forms) – but something new and more complicated. It is that (only) some members of class X end up as all the members of class Y; and moreover, the continuity between members of X and Y is not (usually) due to individual threads, but involves mergers (sexual intermingling) every which way at every generation, over many generations.
Note that, just as we could rephrase mutation as alteration by focusing on a broader class as our subject (‘thing’ instead of ‘X’) – so in the case of evolution, if we focus on a genus common to both the starting and ending species, such as ‘living beings’, the propositional form can be modified to imply a less radical change. For example (excuse me if I have any facts wrong), instead of saying “mesohippus evolved to merychippus”, we might say “equus (the genus of horses) ‘passed from’ mesohippus ‘to’ merychippus”. The words chosen (e.g. passing) are not so important – what matters is that the formal relation involved is quite different.
Such changes of perspective allows us to keep in mind what is unchanging in the midst of change; for instance, throughout the history of evolution, the fact of life has remained a constant, while only its particular expressions have changed.
A new chapter must be written by logicians in the logic of change, treating the propositions concerned with reproduction and evolution in detail. I will not attempt to do the job here, but move on.
The term evolution should first be taken neutrally, to refer to any apparent changes in species of living organisms, since whether such change occurs is also (to begin with) open to debate. Secondly, if such change is admitted, the question arises as to how such change might occur; and here different hypotheses have been proposed, one of them being Darwin’s ‘theory of evolution’ and its later improvements.
Another issue arising in this context is whether such eventual changes can be considered directional in any sense – i.e. whether evolution can be viewed as a sort of ‘conatus’ in the sense described in the previous chapter, giving life the possibility to persist in changing circumstances.
With regard to the first issue, the paleontological and geological evidence at hand is clear: various fossil remains are found in different strata of the earth, which can be scientifically dated by various techniques. It has been observed that earlier strata contain fossil forms that later strata lack, and vice-versa; and in general (with few exceptions), earlier forms have been structurally simpler than later ones. Whence we can infer that life on earth has not always had the same forms: species have come and gone; and in particular, mankind and many other species populating the earth today are relative latecomers.
All our experience shows that life begets life, and no life in our experience emerges from non-life. Granting that later species did not just pop up out of nowhere, but must have come from somewhere, it is reasonable to suppose that they evolved from earlier species. This is called by some the ‘fact’ of evolution, although it is of course based on inference.
Note that such inference involves a movement of thought from ‘difference’ to ‘change’. In the extensional mode of modality, we speak of ‘change’ when we simply mean static differences from one instance of a kind to the next instance of it, because what changes is the appearance of things before the observer as he shifts his attention from one specimen to another. This is different from ‘change’ in the natural (physical, spatial, temporal) mode of modality, which refers to different appearances of the same individual over time.
Such a movement of thought is not in itself epistemologically illegitimate, provided we well understand and remember that it is inductive and not deductive. That is, the extensional mode evidence is used adductively, to confirm the natural mode hypothesis – but it does not definitely prove it. More evidence must be adduced if possible; and no empirical evidence should be found that definitely denies the hypothesis. If we remember that, since we have not actually monitored species giving rise to new species in our lifetimes or in the laboratory, this inference is only based on indirect evidence, we remain open to correcting it if such evidence to the contrary is found.
And indeed, biologists do not only rely on fossil discoveries to support the idea of species change. They also point to morphological, metabolic, genetic and other uniformities, which further strengthen this first hypothesis – indeed, so much as to make it almost undeniable. These analogies, by the way, also involve some inferences from the extensional to the natural mode of modality. It seems reasonable to suppose that similar organisms must have descended from common parents, but it is not totally unthinkable that in fact completely independent parallel trees of life occurred under uniform natural laws.
Say (for the sake of argument, though this description of things is unproved, and one might well ask why it has not recurred since) that life chemically arose in puddles of water filled with ‘organic’ molecules (containing carbon – perhaps amino acids) under the impulse of lightning (an energy input). Two possibilities exist: either the formation of the first living cell was a one-time freak event, from which all life on earth today descends – or many ‘first living cells’ may have thus arisen independently of each other in different places over a long period of time, and given birth to distinct yet similar lines, many though not all of which endured, and some may even have eventually converged (sexually intermingled). The implied question may admittedly not have much importance, but is here raised to emphasize that the mere facts of genetic and other uniformities do not answer it.
Does biology advocate an individual organism at the root of all life on earth, a unicellular equivalent to the Biblical Adam; or is the hypothesis of plurality of first cells to be preferred? One could argue for ‘monogenesis’, by saying that it is less onerous to assume a statistically unlikely phenomenon like the formation of life to have occurred just once than many times. Or one could argue for ‘plurogenesis’ by saying that, once the favorable conjunction of natural conditions was there, random explosions of lightning would likely produce a multitude of such results in scattered puddles over a long time, rather than a unique accident. Since matter generally reacts uniformly to uniform conditions, these first living organisms would likely be similarly composed and structured.
Another, more direct body of evidence for the changes possible in life is the experience of plant and animal breeding by men throughout history, producing varieties with little resemblance to the originals; for examples, how thin wild grasses became rich domestic wheat or barley, or wolves eventually turned into dogs of all shapes, colors and sizes, from Chihuahuas to Saint-Bernards. Nowadays, also, genetic engineering provides evidence of possible change, although so far (to my knowledge) species changes (that are viable and capable of reproduction) have not been demonstrated in the laboratory.
Certainly, anyway, the genetic analysis of all species that is currently underway in biology will resolve a great many or most issues of taxonomy and genealogy. We who are curious about it are very fortunate to be living at this historical time.
Granting the fact of evolution to be a reasonable assumption in the light of all available evidence, the next step is to try and convincingly explain how such change occurs – i.e. its aetiology. Charles Darwin (1809-82) proposed in 1859 a neat theory to explain this phenomenon in a naturalistic manner, i.e. without assuming some mysterious force akin to voluntary agency residing within unconscious living matter, and without appealing to Divine intervention at every turn.
This ‘theory of evolution’ was later improved upon, when the genetics work of Gregor Johann Mendel (1822-84) became known in 1900 (though first reported in 1865). Darwin spoke of biological ‘variations’, but had no clear idea as to how they might occur. Mendel, using quantitative experiments, discovered more precisely how variant characteristics were transmitted from parent to offspring, through what was later called genes. The ‘synthetic’ theory, combining Darwin and Mendel, has been further refined since then.
Our concern here is not biology, but what aetiological lessons we can draw from it. One of the concepts used in evolutionary theory that has to be examined is that of ‘random mutation’ of genes. It should be noted in passing that Mendel had not foreseen genetic mutation, but only variation through the interplay of dominant and recessive genes. It was Hugo de Vries who in 1902 observed that genes could occasionally undergo radical changes. Later, in 1927, some of the agents of such mutations were identified by H. J. Muller; x-rays, UV light and certain chemicals were found to be mutagens.
Genetic mutations are an ordinary, though rare to very rare, part of life. Taken individually, their impact on the species is minimal. It is estimated, for instance, that every human being has about two new mutations in the midst of its 100,000 genes. Over time, a few of these mutations might conceivably become established, but most will not. Mutations do not by themselves determine the direction of evolution.
When biologists speak of random mutations, they mean that the genetic mutations that do occur are not necessarily such as to increase the organism’s overall chances of success in the environment it finds itself in. The mutations might well be beneficial to the organism, or equally well be harmful, or even neutral; also, they might be viable and capable of being passed on to subsequent generations, or again they might well not be so. Therefore, it cannot be claimed that genetic mutations are programmed into the organism, with the quasi-purpose of improving its chances for living. This is emphasized, to exclude any idea that the gene somehow ‘detected’ a certain environmental feature, and mutated in such a way as to better ‘adapt’ to that feature.
Moreover, the term random, spontaneous or chance mutation is not intended to appeal to a notion of natural spontaneity (i.e. to quantum mechanical effects). The mutations are considered caused, in the deterministic sense of causation; we have already mentioned some of the causes or mutagens. Such radiation or chemicals are indeed part of the immediate environment of the genes, causing them to mutate. But the mutation is a mere physical reaction of the gene; it is not akin to a ‘response to stimulus’. It is not necessarily such as to make the organism more resistant to dangerous radiation or chemicals; indeed, very often such mutagens damage the organism irreparably.
Furthermore, terms like ‘chance’ used here are meant to stress the coincidences of events involved. Coincidence refers to two or more chains of events coming together at a certain time and place; they may all be quite determined, and yet their meeting is (relatively) a matter of chance. For instance, an organism may stray into a polluted place, which is not part of its natural environment; e.g. a plant seed blown by the wind or a wandering animal landing in Chernobyl. Here, ‘chance’ could refer to the unpredictability of most purely physical events in practice, even when they are in theory understood; or more broadly, to the possibilities of volition (by animals or humans).
With regard to human volition, we are now quite able to intentionally produce mutations, by applying appropriate radiation or chemicals. More impressive still, is the advent of genetic engineering. In this light, we should enlarge the concept of mutation, including both artificial and natural mutation in it. The term ‘random’ mutation applies only to the latter, and not to mutations due to volitional intervention.
Natural mutations are said to be random to suggest although they of course have physical causes, these are isolated events and not systematic reactions to physiological conditions in the organism concerned or physical conditions in its environment. This idea was intended in opposition to an alternative theory to Darwin’s, suggested by Jean Baptiste Lamarck (1744-1829), that characteristics acquired by parents in interaction with the environment could be inherited by offspring.
The latter thesis would mean that, as its habitat and body goes through changes, from whatever efficient causes, an organism might develop adaptive genetic reactions or responses, which would increase its chances of survival. A sort of regulative or feedback mechanism was implied. In the case of plants (and the equivalent functions within animals), such reactions would be unconscious – events produced directly by purely physical laws. In the case of animals (at least the higher ones, including humans), the reactions could be called ‘responses’, insofar as they might occur indirectly through the mediation of consciousness – i.e. upon seeing (or otherwise sensing, and maybe even conceiving) such and such an environmental or bodily configuration, the organism automatically prepares appropriate genetic changes that increase its chances of survival (or those of its offspring).
Note well that I am not proposing any personal theory here, but only (as a philosopher) considering the variety of conceptual instruments at our disposal, i.e. to develop some sort of flow-chart of possible questions and possible answers. To better understand Darwin’s evolution theory, it is necessary to understand Lamarck’s alternative thesis, since the one is intended in opposition to the other.
It should be noted that the changes of outward characteristics (phenotypes) here discussed are those necessitating genetic mutations (genotypes). We are not concerned with physical (or other) developments that are already programmed as immediately potential in the present genetic configuration, and which may become readily actualized under appropriate environmental, physiological or volitional conditions – for examples, as a muscle may be expanded by exercise, as a skill may be acquired by training or as knowledge may be increased by learning. The Lamarckian thesis suggests that such actualizations of potentials may in turn generate new potentials (logically, of course, the latter are already ‘potential’ – but less immediately so, requiring as they do a restructuring of their underlying matter).
When Lamarckism mentions ‘inheritance of acquired characters’, it refers to such deeper modifications – in the code of life. Some physical or mental event or process, such as the new use of an organ in new surrounds, triggers (perhaps not always, but when a special need for it is signaled) a change in the genetic information, so that the next generation does not need to repeat the acquisition process but has the character by inheritance. Lamarckism claims that genetic mutations may non-randomly result from significant causes like environmental changes or physiological conditions or even intentional work.
The famous example given is that of giraffes, whose necks were thought by Lamarck to have progressively grown each generation ‘so as to’ reach foods higher up on trees; meaning that, upon finding food often too highly placed, individuals strived to reach it, and their genetic material was modified to match the new conditions thenceforth. In this way, according to said thesis, evolution is mechanically ‘programmed’ into life, though in a flexible and not overly mechanistic manner. In other words, genetic mutations are functional events; like blood flow or sensation, they are a means through which life perpetuates life. A conatus is implied: some sort of unconscious striving or tendency to further life is inscribed in the organism.
The Darwinian thesis, on the other hand, while allowing that physical causatives are behind the randomness of genetic mutation (as with any physical event), denies all systematic relationship between specific environments (or resulting internal conditions) and particular directions of change. Mutations may well be – and evidently often are – of no value to life or even antithetical to it. The fact that some mutations seem to conveniently improve the organism’s chances at life in changing circumstances should not be taken as evidence of any inherent loading of the dice in that direction. Random mutation suggests that the chances for favorable mutations are on average no greater than those for unfavorable ones or for mutations that are neither favorable nor unfavorable.
The hypothesis of Lamarck is not unthinkable; a world in which individual organisms are so made as to react or respond to changing conditions constructively, passing on their improvements to their offspring, is conceivable offhand. But biologists have come to the conclusion that the less orderly and predictive hypothesis of Darwin is more congruent with all empirical data discovered or considered to date. Needless to say, I accept that judgment.
Even so, I wonder if we could not still consider Darwinian evolution as an ‘unconscious striving’ of sorts. I ask the question, not out of some reactionary wish to reassert an old idea, but from a philosophical perspective – the need to make a fair assessment of what our common concepts contain and exclude. It seems to me that we can harmonize these at first sight antithetical concepts, as follows.
We could view random mutation collectively as precisely the expedient used by life to statistically ensure its survival in every possible environment it might encounter over time. This supposition is nothing special; analogies can be drawn. We need only look out of our window and see how trees yearly produce thousands of seeds, no two exactly alike, of which maybe one or two specimens at most will give rise to new trees. Life works like that: mass-producing trials on the off chance that some specimens get past the obstacles in their way. Instead of the more obvious Lamarckian expedient of ad hoc genetic changes, nature has apparently opted for reliance on the law of averages.
In that case, random mutations are on the whole life-perpetuating acts, fitting perfectly in the general definition of life as a series of all sorts of self-perpetuating acts. Even though genetic mutations are individually ‘products of chance’, taken all together they constitute one of the resources life has at its disposal for its own survival. In this respect, genetic mutants are essentially no different than genetic variants. They are ‘blind experiments’, in the same way that a root grows straight out till it encounters an obstacle or a mouse unknowingly decides to head due west till it encounters a cat – except that they occur at a more radical level and the opponent they face is the environment as a whole (many different environments) over a long time (many, many generations).
Why presume life has to be either static or changing in orderly ways? It may well be viewed as ‘programmed’ to change in scattered ways. The unpredictable can also be granted the status of ‘conatus’, provided its overall effect is furtherance of life! The fact that some (or even most) blind experiments fail does not disqualify them from quasi-purposive status, since even conscious experiments may fail and fail again yet be considered purposive. By thus broadening our perspective, we acknowledge species evolution, however it occur in fact, as a perfectly natural life process, rather than considering it as an accident. Random mutation is then not an inexplicable dysfunction of genes, but a quite normal function, serving to further vary possible adaptations to possible environmental changes and thus increase the chances of survival of life as such.
Ultimately, life does not (so to speak) ‘care’ what form it takes, so long as it continues. Thus, what seems accidental relative to a particular form of life appears quasi-purposive for life as a whole. If we imagine life on earth as one collective organism, we may assign it an abstract ‘organ’ of genetic mutation. This organ is inherent in the genes in every particular organism, in the way of a mode or law of functioning applicable to genes. From time to time, it churns out random genetic combinations, which may or not prove useful in some circumstances for the maintenance of life on earth.
Thus, without at all denying Darwinism, but on the contrary acknowledging it, we may apparently still affirm evolution as a sort of ‘unconscious striving’.
Another concept worth looking into for aetiological reasons is that of ‘natural selection’. This is the idea that the new characteristics emerging from random genetic mutations may over time persist and spread in a group, either displacing the old ones or coexisting with them. If a characteristic is not compatible with the surroundings, the individuals that have it will naturally pass away and no longer reproduce it; while if a characteristic happens to be more or less adapted to the environment, it will proportionately persist and spread. This is called ‘survival of the fittest’. Of course, if an individual does not reproduce, it is irrelevant to evolution, whatever the adaptability of its genetic content (although it may play an indirect role by otherwise affecting other individuals or the environment).
Here again, the conceptual intention of the principle is determinism, i.e. to explain observed events in terms of causation rather than by means of seemingly more obscure or remote causal concepts. As with random mutation, the basic appeal is to coincidence in a causative context. This hypothesis is preferred to competing ones, like natural spontaneity, some sort of conatus, animist ‘spirits’ or Divine volition, in accord with the general direction of modern science in favor of simplicity and order. Causation is thus (rightly) regarded as the explanatory doctrine to be relied on first and foremost, before any alternatives are even proposed; the latter only come into play when and if causation is found clearly inadequate.
Determinism is claimed in this context, by considering the eventual volition of humans or higher animals as within and part of nature, i.e. as for all intents and purposes a subcategory of causation. That might be justified by arguing that we are here concerned with the lives of species on a grand scale, i.e. over very long periods of time (millions of years). In such case, the impact of individual animal (including human) volitions becomes irrelevant; they average out as if causation was involved.
However, the issue may be further debated, pointing out that when volitional beings affect their own lives or the lives of other volitional beings or of non-volitional beings, determinism is not (strictly speaking) the only causal principle involved. In particular, when animals struggle together and kill each other, or when they eat or otherwise destroy plants, it is not mere causation but volition that is the cause of death.
That such destruction by will, whether intentional, incidental or accidental, has large scale effects on whole species can hardly be doubted. Even in our own lifetimes, we have witnessed mankind destroying a great many species of flora and fauna. Furthermore, we are now just beginning to enter an era of genetic manipulation, which may result in widespread species changes that have nothing to do with natural selection, unless the term ‘natural’ is stretched to include the ‘artificial’ (i.e. the works of mankind and other volitional beings).
Other factors of species change, besides genetic mutation and natural selection, mentioned by biology are gene flow (this refers to movements of individuals from one population group to another, which tends to make populations more uniform), genetic drift (this refers to the chance isolation of populations, which reduces their genetic variety) and non-random mating (including self-pollination by plants, and preferential mating among animals). Note that some of these factors involve consciousness and will.
It should be stressed, too, that living organisms of all kinds constantly modify their mineral environment. The oxygen our atmosphere is graced with started to accumulate only some 2.5 billion years ago, thanks to photosynthetic activity by cyanobacteria; plants re-condition the soil they are in; mankind makes great changes all around it. Thus, though the environment also or mainly depends on factors external to life (the Sun, continental drift, volcanic eruptions, meteors, and so forth), it is to some degree an effect of life. Furthermore, when we speak of ‘the environment’ relative to a given species, we mean not just the mineral world around it, but the world covered by plants and roamed over by all sorts of animals. When discussing natural selection it is well to keep these complications in the concept of environment in mind.
The notion of natural selection is, from its inception, based on analogy to artificial selection. In the latter, the human experimenter chooses individual specimens of a plant or animal possessing certain desired characteristics, and gets them to reproduce; and then again, among their offspring, he selects those he prefers, leaving out those he is not interested in, and gets the new generation to reproduce; and so forth, until he obtains a generation that will reproduce the desired characteristics in all offspring. Natural selection is conceived as similar, except that the selection is not intended by a person, but is happenstance due to the accidents of random mutation and changing natural surrounds; over time, the theory predicts, these accidents also effect certain group changes yielding new uniformities.
The Darwinist concept of evolutionary “adaptation” of species to their environments refers to an essentially passive process. Individuals actively adapt – in the sense that a plant’s roots grow around a rock or its leaves turn to the Sun, or that an animal finds shelter from the storm in a cave or fights a foe and eats it. But species as such ‘do’ nothing other than live on through reproduction of some of their members; they ‘adapt’ only figuratively speaking. Those individuals, if any, that happen to be already genetically adapted to their current milieu in each generation, due to previous variations or random mutations, survive and pass on their genetic code to most of their offspring, which in turn may be well adapted or not, according to their genetic makeup and the environment they encounter.
Species some of whose members continue to be sufficiently (if not perfectly) adapted to their environment continue to exist. If the environment changes over time and all genetic forms (including all random mutations) composing a species are inadequate, the species ceases to exist. If random mutations occur, able to survive in the new changing environment, the species evolves along the same lineage (anagenesis).
Additionally or alternatively, some members of a species may stray into another geographical area and survive. This group may over time change characteristics due to random mutations in its genetic pool, more appropriate to the new environment. Gradually, these variations may become so pronounced that in comparison with the original population a new species has effectively evolved, which cannot reproduce with the old one (speciation). Another group, straying into another geographical area, may evolve quite differently, and form yet another distinct species. Again, although these had common roots, they may have diverged so much that they can no longer interbreed.
This is the Darwinian perspective (roughly put: it has of course been greatly elaborated on and improved since its inception, and continues to be perfected and enriched), and it seems indubitable. It explains so much throughout the science of biology that it cannot be ignored, and has earned general admiration.
However, as pointed out in the previous section, it could be construed as a conceptually narrow view, tracing the courses of particular species. Looking at things more broadly, by considering life on earth as a whole throughout history, or life as such, events may seem more directional. The evolutionary changes of particular species then seem more like effective reactions or responses of the collective living organism of our biosphere to the varying mineral environment external to it, as well as internal interchanges between its various parts (the species and their members). Random mutation coupled with natural selection is simply one of the ‘strategies’ living matter uses to maintain life in a changing mineral, vegetable and animal world.
When life almost disappeared on a number of occasions (for instance, 80-85% of all species, including 95% of all invertebrate marine species in shallow waters, were wiped out some 225 million years ago), the earth’s putative ‘single living organism’ did not die, but was forced to take new forms starting from a more limited genetic pool. Such recoveries took millions of years. But they might be compared (roughly, conceptually) to a lizard losing its tail and growing a new one. Life has all its potential histories within its genetic material. Supposedly, given an eternity and an infinity of environments, every possible form would be tried by life.
Perhaps, also, any life form surviving a mass extinction could give rise to all others again; but it may be that regressions are not always possible. It may be that though humans may evolve from bacteria, the reverse is not true under any circumstances. In the latter case, even if small regressions are occasionally found, evolution may be said to have a direction, from simpler to more complex forms of life. In any event, as Stephen Jay Gould stated: “Wind back the film of life and play it again. The history of evolution will be totally different”.
 See chapter 17 there.
 I refer here to polygenic inheritance, where one trait is a function of two or more genes. Sex-linked traits are an important case in point.
 Such as light or darkness, heat or cold, dryness or wetness.
 Note that the same mutation may occasionally occur in different individuals, although the probability is small.
 In such case K signifies all the molecules that O and M have in common, except those that differentiate them.
 Words are in any case not the issue. The vocabularies of logic and philosophy on the one hand, and of the special sciences (such as biology) on the other, are related but not always identical in connotation. Sometimes, as here, the logical word is more rigidly defined than usual; in other cases, the opposite occurs, as for example with the terms “genus” and “species”, which in logic loosely refer to any overclass and subclass, whereas in biology, they are more specialized.
 We do not yet know the origin of life. Most biologists suppose life naturally arose on earth, when environmental conditions became suitable. But some suggest simple bacteria arrived from outer space attached to meteorites (leaving aside the issue of how, when and where they were formed).
 Although not changes of species, so far as I know. That is, dogs and wolves may reproduce together.
 And I must say, I personally find the idea of genetic manipulation of living beings (especially animals, but even plants) utterly obscene and criminal. My mentioning it is not intended to be an encouragement or a sanction.
 I recently read that fungi are genetically in some respects closer to animals than to plants!
 See Curtis and Barnes, p. 522.
 And indeed, I gather, at some stage by Darwin? However, his final theory is free of this assumption.
 Incidentally, I wonder why some alleles are dominant and others recessive? This seems to me ‘directional’. The value of variety seems obvious: to increase chances of survival under different conditions. But given variety, why are not all variants of a gene equally frequently reproduced? If the dominant allele is so because it is better suited to most conditions, why is the recessive kept on?
 Note that some natural selection is involved in artificial selection, in that fertility may be diminished or lost.
 See Conversations, p. 41.