Here is a brief history of ideas on evolutionary matters. First there is some account of the intellectual background and development of the idea of evolutionary descent. Then a synopsis of the essential structure of Darwin's argument for evolution by natural selection.
What follows is a collection of thumbnail acccounts of, and commentaries upon, some of the main ideas relating to the development of the notion of evolutionary change and diversification.
These notes have been compiled from a diversity of sources, but a particular debt is owed to Ernst Mayr's The Growth of Biological Thought (Harvard U.P.; 1982; all 974 pp. of it)
The run-up to Darwin and beyond is placed in the context of Western European intellectual traditions, since modern scientific ideas and approaches developed there, from beginnings in the Middle East.
Early Greeks They rejected supernaturalism in general, preferring naturalistic explanations of real-worldly phenomena. Though they envisaged an origin for everything, they conceived of a subsequent Steady State, occupying a limitless eternity, albeit with "fluctuations" (recall Heraclitus' dictum: "All is flux" or, more colourfully, "You can never step in the same river twice"[because, in flowing, it changes...]).
Plato Called by some "The Great Anti-hero of Evolution". He generated a series of dogmas, viz.: 1) Essentialism- the metaphysical notion that real-world phenomena and things are variously-deformed representations of fixed ideas or "essences," lying behind them (e.g. Brian Mulrony is only an imperfect representation of "MAN"); 2) The cosmos is a living harmonious entity (shades of Lovelock's Gaia); 3) lying behind this cosmos was a creative power, which started and directs things- the "Demiurge"; 4) The notion of the soul, related to the idea of non-corporeal essences.
Aristotle Contrary to Plato, Aristotle was an empiricist in the main, and inferred a scale of complexity of being, the "Scala Naturae". There was, then, some rational order in the animate cosmos, though he supposed it to be eternal and unchanging.
Monotheistic Religious Systems (0-15th centuries) Through the Dark Ages and most of the Mediæval period, intellectual life was more or less at a standstill under the dead weight of the increasingly dogmatic Organized Church. This stagnation was based on a hardening version of Plato's dogmas: there was no speculation about life, all accepted a "received truth", a recent creation, an impending Armageddon (Judgement Day), and the fixity of creation. All of this was taken to represent the manifestation of an unknowable, but perfect, wisdom.
Intellectual activity in most of the monastic world degenerated into scholasticism and legalism: academic arguments about such things as "how many angels may dance on the point of a needle?" No reference was made to the empirical world. As far as our subject matter is concerned, this world-view meant:
1) the universe, in all its details, was designed by an intelligent creator;
2) this universe is static and constant, the result of a single creative act, and of short duration. This view prevailed until the last 300 years or so, in most of its details. It is important to recognise that this view is a greatly hardened version of that held by the early Christian church, which was, generally, a lot less doctrinaire. St. Augustine, for example, allowed any number of creative acts. But that's another story.
New Trends
from the the study of Physical phenomena came:
The Enlightenment (~ 1740-1840) -this was a time of the French and American revolutions, and the final destruction of feudalism; it was thus a time for ideas on the possibility of change and progress. -philosophers argued about the possibility of an "indefinite perfectability of man". -Leibniz (mainland Europe's counterpart to England's Newton) argued for the continuity and gradualness of indefinite progress (although he saw this as embodying some "inner drive" to progress; such ideas are still with us-see later).
These notions all boiled down to a belief in a single creation by some supernatural being, followed by the development of the cosmos itself and new life forms (which were implicit in the system), by the unfolding of general laws of the cosmos. Thus the idea that: all was created and subsequently directly manipulated by God, changed into: God as the Primary Cause, and the unattended Laws of the Cosmos as Secondary Causes.
This was the time of Linnaeus. His system of classification forms the basis of our current one, but was very different in terms of the philosophy underlying it. The Linnean system was originally very much a Platonic affair, utterly non-evolutionary, dealing with the recognition & ordering of "kinds." These "kinds" were the "essences" of what Mayr has called the Typological Conception of nature.
But there were problems evident in biological philosophising.
By the end of the 18 th. century these were:
Lamarck. In 1800, Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck converted himself into an evolutionist. He needed to do this in order to explain, to his own satisfaction, 1. the apparent increase of organic complexity through geological time, 2. the vast organismal diversity, and 3. the extinction of life forms.
Evidently, he was brought to his conclusion of evolutionary change by inferring phyletic lineages in fossil and recent bivalve mollusc collections. In so doing, he "solved" the extinction problem by phyletic transformation- so forms never actually went extinct! Extinction was an illusion! Life forms merely changed, one into another. Such a model of change also removed the problem of how adaptation could always be so perfect if the physical world changed (people were beginning to realise that it had) but the animate world didn't. Application of this adaptation-based idea of change through time to the diversity problem rendered the many-branchedness of the tree of life intelligible. However, the impulse for such change was seen as an inner drive to greater complexity, derived from the Deity, via adaptational harmony between organisms and environment.
Lamarck was, then, clearly an evolutionist- the first one on record. The crucial difference between his ideas and (to anticipate) Darwin's is as follows:
Lamarck: Environmental change leads to new needs and behaviour in organisms which leads to adaptational variation.
Darwin: Variation always present. Any appropriate variants are "chosen" by the environment (according to how well those variants "fit" that environment, hence the word "fitness" and "fittest."
Lamarck never seems to have reached the idea of common descent - that lineages could be traced back through the generations to common ancestors, and as is well known, he erroneously supposed that evoked adaptations were heritable. But despite their differences, both believed in genuine, gradual change. However, Darwin's emphasis was initially on the diversity problem- species multiplication ("....that mystery of mysteries...."), while Lamarck's stress was on adaptation to the environment. (This is a nice irony, given that we really have made rather little progress in our understanding of speciation, while Darwinian notions have advanced our understanding of adaptation enormously).
In the following century, evolutionary change came to be accepted by
informed scientists, though there was (and continues to be) diversity of
opinion over (the balance of) mechanisms which produce it. There
are six major theories about evolutionary mechanism; each had support
by at least a few folk until the New Synthesis (in the 1940s); some still
have support.
2. The effect of use and disuse; inheritance of acquired characteristics. Lamarck. There have been some recent attempts to revive this notion e.g. by E.J. Steele and R.G.B. Reid (both Canadians!).
3. Direct induction by the environment. This has been revived, in slightly modified form, in some studies of bacteria. Environmental change leads to an increased rate of mutation and the fortuitously more rapid arrival of "useful" mutations.
4. Saltationism (Mutationism). Major leaps of morphology produced by "systemic" mutations. Galton, Bateson, de Vries, Goldschmidt.
5. Stochastic differentiation. Non-Darwinian evolution, i.e. change, by random drift, of neutral, mainly molecular, characters. Kimura et al.
6. Natural selection of undirected micromutational heritable variants.
Darwin, Wallace.
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In physics the world view was of God as the First Cause (the originator and law-giver) with physical laws as Secondary Causes, which thereafter rule the universe.
In biology the materials were so complex, and adaptations so impressive, that Natural Theologians saw intelligent design and purpose everywhere, which spoke to them of harmony, benevolence and wisdom.
This was formalised in the Argument from Design, associated strongly with William Paley who wrote a book (much studied by the youthful Darwin) called Natural Theology. Paley's book is the source of the story about "Paley's Watch" (...the design is so intricate, it unavoidably speaks of intelligent design and purpose... and how much more complex is the structure of a living creature...).
[This is the origin of Dawkins' title: The Blind Watchmaker; he recognises that the explanation of apparent design and purpose is crucial to a successful science of biology, and musters an excellent series of arguments in defence of "a blind watchmaker" (natural selection) as the source of that complexity and fit.]
This whole view of the natural world was embodied in the Bridgewater Treatises - a series of tomes demonstrating God's Design. This was essentially a step back to intervenient Theism - the idea that God acts continually in the world for the benefit of his creation.
But there were problems with this cosy view which just wouldn't go away: how could one reconcile benevolence and omniscience with the phenomena of vestigial organs, predation, parasites, extinction, disease, disasters, and adaptation in a changing world. Hume and Kant had already provided devastating critiques of teleology (the notion that all things were predesigned and purposeful, just steadily unfolding in the fulness of time [to us]) and so the times seemed right for the abolition of pre-destination and design in biology too. But science had nothing to put in the place of intelligent design, and many feared that 'natural' explanations would be destructive of the basis of morality and the fabric of society (sound familiar?). Thus it was that teleological explanations persisted in biology long after they were acceptable to philosophers in general. This was a fine example of the reluctance to face up to the global consequences of the use of rational thought.
Cracks in the plasterwork of the Natural Theology worldview came about
initially from
Eventually the recognition of faunal succession in the fossil record led to the notion of many floods (catastrophism) which periodically destroyed whole faunas, followed by a new, improved, creation (Progressionism).
In its naïve form, progressionism was inherently problematic since it carried the implication that: a) the creator kept getting it wrong, or b) kept on changing his (He was definitely male - not to mention white, and probably British) mind, or c) was capricious. In any event, this directional (teleological) view of history was seriously at variance with the coming dominant geological paradigm of uniformitarianism, which also denied catastrophism and any kind of 'special forces'. The strength of this idea (associated with the name of the Scottish geologist, Lyell), lay in its insistence (à la Ancient Greek) on observable forces, acting in no miraculous fashion, through immense time.
Geological gradualism eventually got a robust empirical basis: the slow build-up of sediments, the nature of volcanic cones, the understanding of the process of erosion. At the time, uniformitarianism was associated with the idea of an indefinitely-long steady state. These ideas clearly flew in the face of progressive development (which did seem well-supported by the fossil record.) In confronting this, Lyell made two points: 1) Though the overall world is in a steady-state, there are many fluctuations about the mean e.g. tropical conditions seemed to have been world-wide during the Carboniferous period. He explained the preponderance of amphibians and reptiles in those times as being appropriate to those climatic conditions. 2) He pointed out that all the details of the fossil record did not in fact support progressionism, citing for example the presence of mammals in the Mesozoic. He also offered the important general observation of the incompleteness of the record.
Lyell believed that all kinds of organisms were always present- merely their relative abundances change with the changing global climate- thus his notion of Steady State Extinction, together with Steady Occasional Creation. Lyell, although he could accept the notion of faunal change, could not apply his own uniformitarianism principles to biology, and admit transformations of form.
So throughout the first half of the 19th. century, there was a steady accumulation of information which seemed to cry out for the conclusion of evolutionary change; many facts which made sense under change, but, under creationism, implied an incompetent or capricious creator.
Though these problems were an intellectual time-bomb, the peaceful Victorian world of harmonious Nature, designed by the benevolent Creator (even if working through natural mechanisms), and clearly for the benefit of man (or at least for Europeans), prevailed until mid-century. Then, in 1844, the British intellectual establishment was shaken by the publication of "The Vestiges of the Natural History of Creation" by Robert Chambers.
It was published anonymously, and caused an enormous scandal and colossal outrage: ".......if our glorious maidens and matrons may not soil their fingers with the dirty knife of the anatomist, neither may they poison the strings of joyous thought and modest feelings by listening to the seductions of this author....". Such a book was, of course, enormously successful, running to eleven editions, and turned out to have been written by the editor of Chambers' Encyclopædia.
Though he was a deist, Chambers asked why organisms should not be influenced, and produced by, natural processes. He argued that: 1) the world's fauna had evolved with time, 2) the changes were slow and gradual, and 3) there was a progression from the simple to the complex. He was the only (published) pre-Darwinian evolutionist in the U.K. and, though his "mechanisms" were absurd, he was enormously important in converting many minds to the possibility of evolutionary change and in provoking the anti-evolutionists (the Natural Theologians) into tipping their debating hand. This was extremely useful to Darwin, who was watching from the wings, who could then find answers for all of their objections before he published his own work.
The reluctance of the intellectual establishment to draw the conclusion of evolutionary change was blown away in 1859 , by Charles Darwin's publication of:
First, let it be said that Darwin used an over-arching consistent pattern of attack on the various problems confronted. It has been said that Darwin wasn't really very bright, that he just stumbled on an idea which was ripe for discovery etc. This notion is considered and trashed effectively in Michael Ghiselin's little book, The Triumph of the Darwinian Method. Darwin's overall approach was to detail a long list of known facts (most of which were hitherto problematic) and show that they could all be rendered intelligible by the adoption of the single idea that evolution had occurred, through descent with modification. He also made clear that, in many cases, an evolutionary hypothesis would require just the pattern observed, and none other. He finally pointed out that special creation would have had to be extremely capricious to have produced all the observed phenomena.
Charles Darwin (1809-1882) as he looked a few years after returning from the Beagle voyage (Dec. 1831-Oct. 1836). |
Darwin in his mid-40s, six years before the publication of "The Origin." |
Darwin in 1874. |
Wallace around the time of the Linnean Society meeting at which the joint paper with Darwin was read. |
Alfred Russell Wallace in old age. |
So, why was Darwin convincing? What were the lines of evidence employed by Darwin?
Remember that the basic questions were 1) diversity and diversification, and 2) adaptation, and that the main impediments to evolution were the notion of constancy of life forms in time and space.
He presented many, independent, lines of evidence for the several elements of his overall view. They may be arranged as follows:
2. The Fossil Record. Using information on erosion and deposition rates, plus knowledge of the thickness of strata, Darwin calculated an age for the earth of ~ 2 x 109 years. This was disputed by the physicist Lord Kelvin (of degrees Kelvin fame), who argued from the mass and composition of the earth, its probable temperature at formation, and the Laws of Cooling that the earth would have reached terribly cold temperatures in such a long period. But Lord Kelvin didn't know about radioactivity....). Darwin also noted a worldwide order in faunal replacement over geological time ("...no group ever evolved twice"). He dealt with the apparently sudden appearance of some forms by observing the incompleteness of the record.
Overall, his inferences were: 1. all forms can be seen as part of a single grand natural system of forms, related to differing extents; 2. the more ancient a form, the more different from related extant forms, usually; 3. close neighbours in the stratigraphic record are very similar, while distant neighbours are usually less so; 4. a given continent's extinct forms are closely related to its own extant forms and not to the forms on other continents; 5. there was, however, the unchanged persistence of certain forms e.g. the inarticulate brachiopod Lingula . These inferences were intelligible under an evolutionary schema, indeed required by it, but special creation need not produce such a pattern, indeed could produce ANY pattern, so why this one?.
1. Common descent and the Natural System The old linear scala naturae was becoming less and less tenable, yet clearly there was a non-arbitrary structure. The evident hierarchical structure strongly argues for common descent; common descent could produce only a hierarchical structure.
2. Common descent and geographical distribution On the Beagle voyage, Darwin was struck by: 1. the fauna of temperate South America was closely related to that of tropical America, rather than to the faunas of other temperate areas elsewhere in the world; 2. the faunas of the Galapagos or the Falkland Islands (Malvinas) similarly showed affinities to the South American continental fauna rather than to other "island faunas." Therefore, distributions were neither random nor uniform; there was, instead, a strong implication of regional historical relationships and of separate development.
3. Common descent and morphology. Pre-Darwinian idealist morphology could not explain the unity of the basic body-plans, no matter how much the parts may be deformed by functional demands. This matter was resolved by the concepts of homology and common descent. Vestigial organs fell into the same scheme. "Attributes are homologous when derived from an equivalent characteristic of the common ancestor." [But proof of homology is often difficult, and requires many lines of evidence............]
4. Common descent and embryology. Why do not embryos take the most direct and efficient path to their eventual adult structure? Why should related organisms be so similar as embryos, yet perhaps very different as adults? Why should terrestrial vertebrate embryos have gill-slits? Why should embryo baleen whales have teeth? "The community of embryonic structure reveals community of descent." In this way Darwin established the barnacles as crustaceans.
To these kinds of evidences we can now add: 1) the study of molecular homologies and phylogenies - the natural system of molecular characters and 2) the grand unity of the genetic code. All of these independent lines of evidence and argument converged on the single idea of common descent with modification. This single idea rendered this entire diverse body of knowledge intelligible. But how did common descent with modification work? How did modification happen?
Darwin dates a particular revelation, leading eventually to the idea of Natural Selection to the reading of Malthus' work on populations on 28 September 1838. But the intellectual structure took a long time to reach its published form. The central argument is delightfully simple, but it issues from the highly complex world of biological entities and processes. But How Does It Work? Darwin made two main arguments, each containing two independent and different lines of reasoning- one inductive, the other deductive. This thinking resulted in the arguments for: 1. Natural Selection and 2. Sexual Selection.
This is the essence of what Darwin called his 'long argument' in "On The Origin of Species by Means of Natural Selection." It concludes that the qualitative composition of populations will change through time such that members of the populations in later generations are better suited to their circumstances (they fit their environment better - hence the term fitness - nothing necessarily to do with physique!).
It is important to recognise that the process of natural selection inevitably follows from the truth of four attributes of populations of things we call "alive." These four things amount to the existence of:
That is, where there is variation in characteristics which consistently correlate with reproductive success, and where such variation is consistently passed across the generations by the machinery of inheritance, and where there are limited (finite) opportunities for survival and/or reproduction, the process of natural selection is an inevitable outcome.
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Note, then, that these four things are empirical matters; therefore, this argument is not simply a "what if?" kind of syllogism, resting on untestable a priori axioms, as are many "truths" in, say, mathematics. Rather, we can objectively evaluate whether these four things really are true of populations of organisms. Of course, they have been evaluated countless times, and we now know them to be near-universal features of life. Therefore, we know that Natural Selection is also necessarily a typical feature of life; some regard it as a law thereof.
Natural Selection is thus not just a hypothetical
mechanism; we know that it must happen, given what we know
of the characteristics of life. What does remain hypothetical
is the rôle of selection in the generation of the diversity of
evolutionary phenomena: how much of all the evolutionary change
we can see and infer is attributable to natural selection? How much
to other causes, such as chance and history?
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This is how Darwin himself expressed the idea [interpretations
in square brackets]:
NOW THINK ABOUT THIS: Given the above, we know that selection is a fundamental feature of life; we also know that chance is a fundamental feature of everything. We are used to regarding chance - randomness - as our null hypothesis i.e. as representing the most parsimonious explanation of phenomena. This is certainly a reasonable approach in the physical world, but in evolutionary biological systems - populations of organisms - it is not altogether clear that phenomena based in chance (e.g. genetic drift) have any logical priority over those based in selection. If we can't reject chance as an explanation, we might also be advised to check if we can reject selection scenarios before we rush to conclude that drift, say, is the most parsimonious explanation......... that might be stacking the deck to favour the domain of chance.........................
Although the possible importance of historical and chance phenomena must be kept in mind in devising explainations of a given phenomenon, I feel one can only proceed using a frankly-stated Selection Paradigm, since it permits progress in analysis. Selection is, in many ways, the most parsimonious paradigm to hold (as opposed to one of randomness, say).
SO THINK AGAIN ABOUT THIS: We are used to thinking these days of testing our explanations against a null hypothesis. We are also used to framing null hypotheses in terms of random or chance models. We do this because of the notion that randomness is, in some sense, the lowest order of determination of things. But it is not atall clear, in biology at least, that randomness has any logical priority in claims of parsimony (simplicity), over Natural Selection. After all, we know that organisms show heritable variation in characteristics relevant to survival/procreation probability, and that the world and its resources are finite. Therefore we know selection to be operating, just as we suppose we know chance to operating.
Some philosophers of biology have suggested that, in biology, a selection model has prior claim on explanation, ahead of chance........................
Returning to our theme, in Darwin's whole scheme, as mentioned above, there is:
Generally, there was much opposition to selection, even though most scientists rapidly adopted an evolutionary view. Selection was not generally accepted until the rediscovery of Mendel's results, and the Evolutionary Synthesis, almost 100 years later. The idea of selection was resisted for eight main reasons:
1. As we've seen, almost all were convinced Essentialists and didn't think in terms of variability or of populations. Related to this was a rejection of the idea of "improvement."
2. Almost all took a teleological view of nature: there was automatic perfection. where, then, is the role for selective change?
3. It was believed that any natural variation would very quickly become exhausted by selection. (This objection is based in the rudimentary understanding of the day of the nature of variability in natural populations; this persisted into the 20th. century, and was the basis of bloody exchanges among the founders of the science of genetics. Yes, it's true folks, genetics, the scientific study of inheritance, grew out of evolutionary science; how quickly we forget.)
4. The difficulty in imagining the transition (always envisaged as a jump- see 1.) to another species.
5. Many rejected the hypothesis because they felt that if you deny design, then all must be "by accident." Even today, there are many with this problem: "How could DNA have arisen by accident?" ask Hoyle & Wickramasingh. Answer: It didn't. Natural Selection has two components: Accidentally arising, random-direction variation, followed by an ordering due to the selection of phenotypes- the very antithesis of randomness. A simple idea, but so easily misconstrued by the highly-trained mind..... Many philosophers and "hard" scientists still wrestle with this subtle mixture of chance, propensity and probability.
6. Objections from then-current philosophy of correct scientific practice. Darwin's hypothesis was not based wholly on induction (then the rage), or on experiment. Recently, the philosopy and practice of science has caught up.
7. The absence of "proof." Of course, it is a common misconception, even among scientists and science teachers, that science is about proof (or about "facts.") The Creationists use this one too. But on this topic, there are now legions of clear demonstrations of the action of effective selection in the wild.
8. There were several empirical objections, some potent until quite recently: 1) Blending inheritance. Darwin believed in it, and it gave him some problems and embarrassment, but Mendel's findings refuted it; 2) How could slight adavntages make any difference in the real world? Now demonstrated extensively; 3) Limits to the response to selection? 4) How could selection be extrapolated to major taxonomic differences?
Although not a scientific objection, there was an extremely powerful societally-based objection to whole idea of natural processes ("...........from below...") producing organic complexity, because the analogies with human society were so obvious. It was entirely clear to the average gentleman of society that everything worthwhile came from the organising principles provided from above, by the aristocracy and their hangers-on. To admit that the whole world had been built on contrary principles seemed to be digging away the entire foundation of society. In addition, many found a difficulty with the name "selection" because of its ambiguity- is it an agent? a force? a process? the result of a process? (try these questions for yourself. Go on, try.) Some thought that N.S. simply replaced "God" with "Nature", busily selecting away..............
Because of this difficulty, in later editions of the Origin, Darwin introduced the phrase, borrowed from Herbert Spencer:
Following Darwin was a proliferation of alternative ideas which generated a grandly acrimonious debate, lasting over 70 years (out of which grew Population Genetics- see Bio 366 for more), about such matters as: inheritance of aquired characteristics ("soft inheritance"); evolution by "gradualism" or "saltationism"
A true schism developed around these matters and the blood flowed (all over the pages of Nature). On one side were experimental biologists working, in the lab. mostly, on embryology, cytology, genetics and behaviour, and on the other, there were whole-animal types with a training as field naturalists. Essentially, the difference was over the mechanism and role of mutation.
The adaptationist-naturalists didn't much care about the origin of variation- they took it as a given- but saw mutations as of small effect, hence gradualism, and saw selection as all-important.
The mutationist-lab. biologists disagreed: they maintained that most population variation is non-heritable noise. They saw evolutionary change as deriving from major mutations-saltationism. They saw selection as insignificant beside this.
Around 1940, the so-called Evolutionary Synthesis (of biology, palaeontology and genetics) was achieved:
1. (All) evolution is gradual, explained in terms of selection among slightly-differing variants due to small-effect micromutations and their recombination. Hard inheritance only.
2. Species are seen as composed of reproductively defined groups of populations.
3. The application of selection to such populations can produce all higher-level phenomena (e.g. cladogenesis - the splitting of lineages).
This synthesis required abandoning ideas like mutation-pressure and macromutation, accepting the ubiquity and importance of selection, and the prevalence of natural variation. This synthesis was, to some extent, a statement of many people's best-guess about things, quite well in advance of good empirical evidence. However, it was known that selection could have significant consequences in the field, and that many apparently trivial characters could have survival value. Genetics theory had also demonstrated the potential power of even low levels of selection in changing the composition of populations.
So we know that selection is probably ubiquitous and can easily have
significant effects; we have no good reason yet to suppose that mutations
are anything other than at random with respect to environmental factors;
most mutations seem to be point mutations. So what's left?
Fundamental questions of concern in contemporary evolutionary biology include:
1. The power of selection is much debated. It has several aspects; they mostly interact with the issue of selection's sufficiency and the importance of other agents of change. Can selection erase phylogeny? If so, this presents problems for homology and taxonomy and on and on......... How important are drift, gene flow, founder effects..?
2. The consequences of selection, supposing it to be important, are to be investigated. What should follow in nature if selection is important? Our basic answer to this is that we would expect virtually all elements of morphology and behaviour to be efficient solutions to the problems of survival and procreation. Selection is a calculus of increasing efficiency; we can apply this realization to generate expectations (predictions) about a diversity of characteristics, thus:
3. What are the components of fitness? Or, what does selection operate on? In the viability/survival dimension we can specify: 1) competition for resources, including space, and 2) surviving environmental challenges, including predation and parasitism. In the procreation realm we have: 1) getting mates, 2) age at maturity, fecundity etc., and 3) parental care patterns. You will recognise these as topics of great current interest in modern ecology. This is no accident. They are so interesting because in the last 25 years, ecologists and ethologists have used "selection thinking" as a potent research strategy for identifying important questions and generating powerful predictions. Asking "fitness questions" is central to the pursuit of modern evolutionary biology.
4. Given all of that, what is the TARGET
of selection? what is the unit of selection? what is
the path of its operation?
5. How much of the picture can be explained by selection? Is there such a thing as species-selection? How important is lineage sorting? Is speciation explicable by selection alone, or are other things going on? What is the importance of the Punctuated Evolution ideas?
6. Can genetic information be transferred
among lineages? It is part of the central synthesis
that mutations can only be passed on to offspring. But there is currently
much interest in things like plasmids etc. which are capable of injecting
genetic information into alien genomes. Indeed, one very persuasive
point of view has it that all eukaryotes are composed of symbiotic, once
independent, bacterial organisms - the eukaryote organelles - mitochondria,
plastids, even the flagella and centrioles - were originally bacteria which
invaded, carrying their DNA.................