Evolution As It Was Meant To Be
A work in progress by Stephen L. Talbott
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Evolutionary theorists tend to become frustrated when many of the rest of us fail to “get” the revolutionary and convincing simplicity of natural selection, that primary engine of adaptive evolution also known as “the survival of the fittest”. For example, Niles Eldredge, a paleontologist and, for several decades, a curator at the Museum of Natural History, has wondered, “Why do physicists, who have the reputation of being among the best and the brightest, have such a hard time with the simple notion of natural selection? For simple it is”. He then quotes Charles Darwin:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring Struggle for Existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected.
“The concept”, Eldredge writes, “is definitely simple enough. This description of natural selection may be a bit longer than the elegantly brief F=MA [force equals mass times acceleration — Newton’s second law of motion]. Conceptually, however, it is hardly more complicated” (Eldredge 2000, pp. 89-90).
The simplicity of what is being promulgated as “natural selection” can hardly be doubted. In his landmark book on The Nature of Selection, the philosopher of evolutionary theory, Elliot Sober, considered it “remarkable that a hypothesis of such explanatory power could be so utterly simple conceptually: If the organisms in a population differ in their ability to survive and reproduce, and if the characteristics that affect these abilities are transmitted from parents to offspring, then the population will evolve” ("Sober 1984, pp. 21-2).
The idea of natural selection seems so straightforward and conclusive that it forces its way into the receptive mind without much need for evidence. August Weismann, whose importance for nineteenth-century evolutionary theory has been considered second only to Darwin, rather famously wrote in 1893 that we must accept natural selection as the explanation for the wondrous adaptation of organisms to their environments “because it is the only possible explanation we can conceive”.
Further, according to Weismann, “it does not matter” whether we can demontrate the role of natural selection in particular cases. “Once it is established that natural selection is the only principle which has to be considered, it necessarily follows that the facts can be correctly explained by natural selection” (quoted in Gould 2002,p. 202).
The compelling simplicity of natural selection, according to Ernst Mayr, is so pronounced as to have proven a stumbling block for many. Mayr, whose influential career spanned the entire, twentieth-century history of the modern evolutionary synthesis, proposed that “startling simplicity was the most formidable obstacle that the selection theory had to overcome. Students of the phenomena of life found it undignified to explain progress, adaptation, and design in nature in so mechanistic a manner” (Mayr 1964, p. xviii).
Brief summary statements of the simple logic of natural selection abound. In philosopher Daniel Dennett’s succinct formulation, “evolution will occur whenever and wherever three conditions are met: replication, variation (mutation), and differential fitness (competition)" (quoted in Lenski et al.). Or, expanding the idea just a little, we might say that evolution is guaranteed to occur under three conditions:
With various terminological variations, that is how natural selection is presented in numberless textbooks. According to the influential popularizer (and noted theorist) of evolutionary theory, Stephen Jay Gould, the basic idea has the simplicity of a syllogism. He referred to it as the “syllogistic core” of natural selection (Gould 2002, pp. 125-6n). For Dennett, this core is a “mindless” recipe, or algorithm, — one so obvious and universal that it could be derived even without reference to organisms, while nevertheless offering “guaranteed results” in biology. The algorithm is “Darwin’s dangerous idea” and, its wholly abstract, materially indifferent character notwithstanding, it is the key to making sense of everything from the simplest irritable cell to human meaning, cognition, culture, and morality (Dennett 1995, pp. 51, 163-81).
Variation, inheritance, and survival of the fittest: for a certain mindset (well-established in our day), something does indeed seem irresistible and self-evident about the way these conditions testify to the idea of change. And — Eldredge’s obtuse physicists apart — more than enough students of evolution do seem smart enough to “get” the extraordinary power and simplicity of natural selection. The widely read British psychologist and science writer, Susan Blackmore, speaks for many when she says that “evolution is inevitable — if you have information that is copied with variation and selection then you must get [quoting Dennett] ‘Design out of chaos without the aid of mind’”. Blackmore goes on almost rapturously: “It is this inevitability that I find so delightful — the evolutionary algorithm just must produce design, and once you understand that[,] you have no need to believe or not believe in evolution. You see how it works” (Blackmore 2014. Emphasis in original).
It is perhaps not often enough asked whether the simplicity, universality, and persuasive force of the algorithm belong only to the algorithm, or also to life. In 2003 Christoph Adami, who was then head of the Digital Life Laboratory at the California Institute of Technology (Caltech), was quite sure the answer is “both” when he defended the value of trivially simple and non-living “digital organisms” — bits of computer code representing genes and living processes — for teaching us about evolution. The principles of evolutionary theory, he said, are “very, very general, and very simple”, so that our predictions “don’t depend on these little details of molecular biology” (quoted in O’Neill 2003). It’s almost as if actual phenomena become irrelevant to the researcher, who needs only to work out a simple logic.
Our unease only grows when we hear Richard Dawkins discussing how some animals cleverly coerce the behavior of others. For anyone skeptical of his explanation, Dawkins had this word of encouragement: “With natural selection working on the problem, who would be so presumptious as to guess what feats of mind control might not be achieved?” (Dawkins 2008, p. 71). One almost hears an echo of the parent trying to soothe a child’s perplexity about some puzzle of creation: “Surely God could do it”.
And, indeed, over-estimation of the explanatory power of natural selection may be why Darwin’s contemporary, the geologist Charles Lyell, accused him of “deifying” the theory.1 A century later, in 1971, Lila Gatlin, a biochemist and mathematical biologist who figured centrally in developing the conception of life as an “information processing system”, could summarize contemporary usage by saying, “the words ‘natural selection’ play a role in the vocabulary of the evolutionary biologist similar to the word ‘God’ in ordinary language” (quoted in Oyama 2000a, p. 31). Such is the power of logical constructions over the human mind.
No doubt the “evolutionary algorithm” truly is simple, and its logic, as far as it goes, is self-evident. But we might want to keep in mind how thin and unstable is the strip of intellectual real estate between “self-evident” and “vacuous” — especially when, as scientists, we prefer abstract logical necessity and simplicity to “little details”, such as the difference between a computer program and the life of a tiger or octopus.
We heard Elliot Sober marvel at the “explanatory power” of a simple proposition: “if the organisms in a population differ in their ability to survive and reproduce, and if the characteristics that affect these abilities are transmitted from parents to offspring, then the population will evolve.”
This is a strange claim, given that it is flatly false — false in the sense that nothing in the logic of the theory tells us that populations must evolve in a manner that yields new species or fundamental changes of “type”. We know that healthy populations do exhibit plasticity, variation, and adaptability — a spruce tree growing in the lowlands will differ greatly from one growing near the alpine treeline, and one tree will differ from its neighbor — but this variability does not by itself imply the evolutionary origin of the diverse forms of life on earth.
For millennia all species were widely assumed to remain constant according to their “essential” nature. Certainly untypical variation could occur, but this only reminded our ancestors that defective organisms tended to be removed — part of the means by which the character of the species was preserved. So how did we learn that the situation was quite otherwise, and that species did evolve?
Surely the largest factor was the discovery and systematic investigation of fossils. Seeing was believing. It was the apparent historical record, not the logic of natural selection, that settled the question for us. Look at it this way: everything depends on what organisms actually do — and, as has long been recognized, one of the most remarkable things they are capable of doing is to give consistent, generation-by-generation expression to the character of their own kind. Whether that kind needed to be understood as a static or dynamic reality could only be resolved through empirical investigation.
Moreover, once we see that species have in fact evolved, we are still left with the most basic questions about how they have done so:
I can think of no fundamental question about evolution whose answer is suggested by the advertised formula for natural selection. Everything depends on what the amazingly diverse sorts of organism actually do as they respond to and shape their environments. Contrary to Susan Blackmore’s exultant insight, nothing in the “algorithmic logic” of natural selection tells us that evolution must have happened — and, given that it has happened, the logic by itself tells us little about what we should expect to find in the fossil record. We may ask then, “What, in truth, is being celebrated as the revolutionary principle of natural selection?”
None of this is to deny the trivial validity of the idea of natural selection. Of course organisms that are “fitter” will generally do better in life than “unfit” organisms. That’s how we define “fit”. And of course a record of the winners and losers in the “struggle for survival” will tell us a great deal about evolutionary processes. Or could tell us if we understood all that happened in order to establish this particular record. It is hardly unreasonable to point out that we will gain a profound understanding of evolution only when we know a fair amount about how it has happened among actual organisms and along its broad course down through the ages.
Every organism’s life and death encompasses and, so to speak, “sums up” a vast range of purposive activities, not only on its own part, but also on the part of many other organisms. One might feel, therefore, that the “theory” of the survival of the fittest can explain just about everything. Certainly the overall pattern of births and deaths must yield the observed evolutionary outcome! Actually, it just is that outcome — it is the pattern we need to explain — which doesn’t yet give us much of a theory.
The miracle of it all is that, if evolutionary rhetoric is to be believed, the empty formula of natural selection explains just about everything you could imagine — all based, as this rhetoric consistently informs us, on some form of “blind” agency. Natural selection is always doing things. And so we hear about the mechanism of selection, as well as the forces or pressures that operate in it. We learn that natural selection shapes the bodies and behaviors of organisms, builds specific features, targets or acts on particular genomic regions, favors or disfavors (or even punishes) various traits or behavioral strategies, operates in this way or that, maintains DNA sequences, promotes adaptation of populations to local environments, polices mutations, and, in general, causes an endless variety of effects. Darwin himself spoke about how
natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. (Darwin 1859, p. 84)
This sort of language is all but universal. I think it is safe to say that relatively few references to natural selection by biologists fail to assert or imply that we are looking at something like a humanly contrived mechanism with the well-designed power to do things, beginning with the activity of selecting. This guiding activity is effected in the sophisticated and almost incomprehensibly well-organized manner necessary to create new forms of the most complex and mysterious entities known to us — living organisms.
If what biologists say has any significant bearing on what they mean, then they are telling us, emphatically, that natural selection is an effective, mechanistic agent — an agent of evolutionary change. This is a problem. Developmental systems theorist Susan Oyama was fingering it when she cautioned,
Nature is not a deciding agent, standing outside organisms and waving them to the right or the left. However much we may speak of selection “operating” on populations, “molding” bodies and minds, when the metaphorical dust has settled, what we are referring to is still the cumulative result of particular life courses negotiated in particular circumstances. (Oyama 2000b, p. 81)
Some evolutionists are uncomfortably aware that their use of a phrase intentionally evoking the breeder’s “artificial selection” invites mystical belief in a breeder-like agent supervising adaptive evolution. And so they assure us that “natural selection”, despite its explicit suggestion of a selecting agent, is “just a metaphor”.
The prolifically blogging defender of evolutionary orthodoxy, University of Chicago geneticist Jerry Coyne, spells it out this way: natural selection “is neither a ‘law’ nor a ‘mechanism’.” If we explain the evolution of coat color in polar bears as “‘natural selection acting on coat color’, that’s only our shorthand … There is no external force of nature that ‘acts’ on individuals. There is only differential replication of genes” (Coyne 2010).
In other words, as Coyne goes on to say, the language of agency really refers to a mundane process — “a process that is inevitable”, he adds — and here, as expected, he cites the familiar logic of natural selection.
But it is hard to see this as anything but subterfuge. There is a reason why no effective verbal alternative to the painfully tendentious “selection” has taken hold. The idea of a selecting power is deeply rooted and seemingly ineradicable from the modern biologist’s thinking about evolution. Yes, we can redefine the “metaphorical” selecting agent as a process. But if we then say that the process inevitably yields exactly the results previously ascribed to the intelligent agent — yields what can be viewed as the policing, targeting, sculpting, and creating of organisms and their features — we are not getting rid of the agent. We are merely giving it a different name.
It would be well for all evolutionists to cheerfully admit what I am quite sure even Coyne believes — that nature, in their conception, just happens to work in such a way that it is in fact a kind of agent, accomplishing exactly the kinds of things agents accomplish. Nature is, in Richard Dawkins’ terminology, like a watchmaker.
This admission, when made fully explicit, might reasonably lead to a reflection upon the true sources of the imagined evolutionary agency — a reflection beginning with an acknowledgment of the empirically empty nature of the familiar logical formulations of natural selection. And this in turn could prompt a valuable inquiry: where do we see an actual play of agency, as material accomplishment, other than in the lives of organisms? Is there anything beside this accomplishment — this infinitely varied play of well-directed life narratives I have tried to touch upon in the first half of the book — to give empirical substance to our evolutionary theory?
But do not underestimate the difficulty of coming around to such fundamental questions. Regarding the “syllogistic core” of natural selection, Gould wrote that “nearly all textbooks and college courses present the ‘bare bones’ of natural selection in this fashion (I have done so in more than 30 years of teaching).” After suggesting that this presentation “does not permit a teacher to go beyond the simplest elucidation of selection as a genuine force that can produce adaptive change in a population”, he goes on to say: “In other words, the syllogistic core only guarantees that selection can work … [it] can only rebut charges of hokum or incoherence at the foundation” (Gould 2002, p. 126n; emphasis added).
It would be truer to say that the famously simple and compelling logic of natural selection, misconceived as the “foundation” of a powerful theory, has been a primary source of hokum in evolutionary thinking. It is a kind of blank template upon which overly credulous biologists and lay people can project their faith. As for the “genuine force” Gould refers to — a supposed causal power over and above those we find actually at play in biological activity — it is a magical invention borne of the refusal to recognize agency in the only place where we ever observe it, which is in the lives of organisms.
This is not to deny that we have learned a great deal — for example, from paleontology and molecular studies — under the banner of “natural selection”. After all, the vagueness of the logical template allows the biologist to impose the required theoretical form upon just about any investigative work. Whatever it is that actually happens, we can always say that the resulting organisms were “selected”. The question is whether the theory adds very much, beyond a certain illusion of explanation, to the otherwise informative results of the ongoing work.
It happens that the explanatory vacuity of the logic of natural selection has been recognized by some of the most prominent and reputable evolutionary biologists for more than 150 years. They have been concerned about how complex adaptive innovations are achieved, and how, in general, we can make sense of the evident creativity in evolution. The question that nagged at them can be put this way: What does natural selection select — where does selectable variation come from — and why should we think that the mere preservation of already existing variants, rather than the creative production of those variants in the first place, directs evolution along the trajectories we observe?
The influential Dutch botanist and geneticist, Hugo de Vries, framed the matter this way during the first decade of the twentieth century:
Natural selection is a sieve. It creates nothing, as is so often assumed; it only sifts. It retains only what variability puts into the sieve. Whence the material comes that is put into it, should be kept separate from the theory of its selection. How the struggle for existence sifts is one question; how that which is sifted arose is another.2
It was de Vries who gave currency to the catchy phrasing that has since been repeated many times: “Natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest”.3 The concern is not easily dismissed. Other biologists have added their own accents to the general theme, and it is worth pausing a moment to trace a theme that some might see as a kind of subterranean, or largely hidden, history of evolutionary thought — a history beginning no later than the year after the original publication of The Origin of Species in 1859:
“If we take the three attributes of the deity of the Hindoo Triad, the Creator, Brahma, the preserver or sustainer, Vishnu, and the destroyer, Siva, Natural Selection will be a combination of the two last but without the first, or the creative power, we cannot conceive the others having any function.” (Sir Charles Lyell , Scottish geologist who laid the crucial uniformitarian foundation for Darwin’s theory)
“It is exceedingly improbable that the nicely adapted machinery of animals should have come into existence without the operation of causes leading directly to that end. The doctrines of ‘selection’ and ‘survival’ plainly do not reach the kernel of evolution, which is, as I have long since pointed out, the question of ‘the origin of the fittest’ … The law by which structures originate is one thing; those by which they are restricted, directed, or destroyed, is another thing.” (Edward Drinker Cope [1887, p. 225], noted American paleontologist and formulator of “Cope’s Rule”, which proposed that the organisms of an evolutionary lineage tend to increase in size over time)
“Selection permits the viable to continue and decides that the non-viable shall perish … Selection determines along which branch Evolution shall proceed, but it does not decide what novelties that branch shall bring forth.” (William Bateson [1909, p. 96], a founder of the discipline of genetics)
“The function of natural selection is selection and not creation. It has nothing to do with the formation of new variation.” (Reginald Punnett , British geneticist who cofounded the Journal of Genetics; quoted in Stoltzfus 2006)
“The actual steps by which individuals come to differ from their parents are due to causes other than selection, and in consequence evolution [by natural selection] can only follow certain paths. These paths are determined by factors which we can only very dimly conjecture. Only a thorough-going study of variation will lighten our darkness.” (J. B. S. Haldane [1932, pp. 142-3], a major contributor to the twentieth-century consensus theory of evolution)
Regarding specific traits, natural selection “might afford a reason for their preservation, but never provide the cause for their origin.” (Adolf Portmann [1967, p. 123], preeminent zoologist of the middle of the twentieth century)
“Natural selection is the editor, rather than the composer, of the genetic message”. (Jack King and Thomas Jukes , key developers of the idea of “neutral evolution”)
“In evolution, selection may decide the winner of a given game but development non-randomly defines the players.” (Pere Alberch , Spanish naturalist and embryologist, sometimes spoken of as the founder of Evo-Devo — evolutionary developmental biology)
“Natural selection eliminates and maybe maintains, but it doesn’t create.” (Lynn Margulis , microbiologist and botanist, pioneer in exploring the role of symbiosis in evolution, and co-developer of the Gaia hypothesis)
I referred above to a “subterranean, or hidden, history”. But, given that this list of observers reads almost like a Who’s Who? of the history of evolutionary theory, those terms hardly seem appropriate. Rather, the situation reminds me of what I referred to as “Biology’s Blindsight” in Chapter 2, “The Organism’s Story”.
I noted there how biologists cannot help recognizing the narrative and purposive meaning of living performances. This is indicated, for example, by their delineation of research topics, which have to do with how one or another organism performs particular tasks. Rocks and rivers do not have tasks. Yet, these same researchers avoid explicit acknowledgment of this meaningful activity in their scientific descriptions. That is, the end-directedness defining the problem they set out to explain disappears from the terms of their explanation, which therefore is not an explanation of the original problem. It is a physical characterization, which certainly has its own value. It’s as if we set out to understand a scientist’s technical papers, and ended up describing only the physical processes of writing and publication, blind to the meaning we were at first eager to apprehend.
Of course, biologists do not flatly deny the all-too-obvious, task-oriented activities of organisms. Instead, these are projected upon images of machines and programs. One speaks of organisms in the language of mechanism. Since machines are always understood in terms of intelligent design — the engineering design imprinted upon their structure — this projection subconsciously (if rather miraculously) “accounts” for the end-directed activity and soothes the cognitive disconnect between what one knows and what one allows into theory.
In the case of evolution, the same result is achieved by projecting the repressed knowledge of living agency upon the always available blank slate and god-like power, or “mechanism”, known as “natural selection”.
And so the repeated glimpses of the truth evidenced in the list of remarks by the authorities above have had little effect upon the history of the science. Indeed, it may well be that most of those authorities only dimly perceived the full implications of their own words. The habitual, blindsighted predisposition of the entire discipline of evolutionary biology — including the projection of the repressed awareness of agency — has been too powerful to allow a clean escape to those trained in it.
It seems to have been the task of biology over the past couple of centuries to reconceive living things without their life — to see the world of organisms, not through their own eyes, but through ours, which are as if hypnotized by the well-designed automatisms that now shape every dimension of our existence. It is not often that the spell is momentarily broken, as when the philosopher of biology, Denis Walsh — after noting the indisputable yet ignored truth that “organisms are fundamentally purposive entities” — expressed his perplexity by asking, “Why should the phenomenon [of agency] that demarcates the domain of biology be off-limits to biology?” (Walsh 2015, p. ix).
And yet, even Walsh, wonderfully insightful as he is, proceeds to characterize the organism’s agency in a strictly materialistic manner, as if it could be understood without accepting at face value the inner dimensions of life — cognition, thinking, intention, volition. We are given agency without agency, life without life. Such is our way today. It is my intention in the following discussion of evolution to articulate a different point of view, taking life in its own terms. And I see no reason to exclude what we know most directly — and in a higher key, so to speak — through our own existence as organisms.
This higher key offers us many possibilities for an immediate, inner understanding of our experience, which is hardly grounds for excluding ourselves, or our understanding of the meanings of life, from a science of organisms.
1. This according to philosopher of biology John Beatty (2010, p. 23), citing correspondence between Darwin and Lyell.
2. Quoted in Gould 2002, p. 428.
3. de Vries 1906, p. 826.
Alberch, Pere (1980). “Ontogenesis and Morphological Diversification”, American Zoologist vol. 20, pp. 653-67. doi:10.1093/icb/20.4.653
Bateson, William (1909). “Heredity and Variation in Modern Lights” in Darwin and Modern Science, edited by A.C. Seward, pp. 85-101. Cambridge UK: Cambridge University Press. Text available at http://www.gutenberg.org/ebooks/1909
Beatty, John (2010). “Reconsidering the Importance of Chance Variation”, in Evolution: The Extended Thesis, edited by Massimo Pigliucci and Gerd B. Müller, pp. 21-44. Cambridge MA: MIT Press.
Blackmore, Susan (2014). “A Hundred Walked Out of My Lecture”. Available at https://richarddawkins.net/2014/08/a-hundred-walked-out-of-my-lecture
Cope, Edward Drinker (1887). The Origin of the Fittest: Essays on Evolution. New York: D. Appleton and Company.
Coyne, Jerry A. (2010). “The Improbability Pump”, The Nation (April 22). https://www.thenation.com/article/improbability-pump/
Darwin, Charles (1859). On the Origin of Species, first edition. London: John Murray. Available at https://archive.org/details/onoriginofspecie00darw_0
Dawkins, Richard (2008). The Extended Phenotype, revised edition (1999), reprinted with corrections (2008). Oxford: Oxford University Press. Original edition published in 1982.
Dennett, Daniel C. (1995). Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon and Schuster.
de Vries, Hugo (1906). Species and Varieties: Their Origin by Mutation. Lectures delivered at the University of California, edited by Daniel Trembly MacDougal, second edition. Chicago: Open Court. Originally published in 1905. Full text available at http://gutenberg.org/ebooks/7234.
Eldredge, Niles (2000). “The Pattern of Evolution”. New York: W. H. Freeman and Company.
Gould, Stephen Jay (2002). The Structure of Evolutionary Theory. Cambridge MA: Harvard University Press.
Haldane, J. B. S. (1932). The Causes of Evolution. London: Longmans, Green and Co.
Holdrege, Craig (1999). “What Does It Mean To Be a Sloth?” NetFuture #97 (Nov. 3). Latest version is available at http://natureinstitute.org/nature/sloth.htm
King, Jack Lester and Thomas H. Jukes (1969). “Non-Darwinian Evolution”, Science vol. 164, no. 3881 (May 16), pp. 788-98. doi:10.1126/science.164.3881.788
Lenski, Richard E., Charles Ofria, Robert T. Pennock and Christoph Adami (2003). “The Evolutionary Origin of Complex Features”, Nature vol. 423 (May 8), pp. 139-44. doi:10.1038/nature01568
Lyell, Sir Charles (1860/1970). Sir Charles Lyell’s Scientific Journals on the Species Question, edited by Leonard G. Wilson. New Haven CT: Yale University Press. Yale Studies in the History of Science and Medicine, no. 5.
Margulis, Lynn (2011). “Discover Interview: Lynn Margulis Says She’s Not Controversial, She’s Right”, Discover (April). Available online at http://discovermagazine.com/2011/apr/16-interview-lynn-margulis-not-controversial-right
Mayr, Ernst (1964). “Introduction”, On the Origin of Species: A Facsimile of the First Edition, by Charles Darwin, pp. vii-xxvii. Cambridge MA: Harvard University Press. doi:10.1038/nature01568
O’Neill, Bill (2003). "Digital Organisms", PLOS Biology. doi:10.1371/journal.pbio.0000018.
Oyama, Susan (2000a). The Ontogeny of Information, 2nd edition, foreword by Richard C. Lewontin. Durham NC: Duke University Press. First edition published in 1985 by Cambridge University Press.
Oyama, Susan (2000b). Evolution’s Eye: A Systems View of the Biology-Culture Divide. Durham NC: Duke University Press.
Portmann, Adolf (1967). Animal Forms and Patterns: A Study of the Appearance of Animals, translated by Hella Czech. New York: Schocken.
Sober, Elliott (1984). The Nature of Selection: Evolutionary Theory in Philosophical Focus. Cambridge MA: MIT Press.
Stoltzfus, Arlin (2006a). “Mutationism and the Dual Causation of Evolutionary Change”, Evolution and Development vol. 3, no. 3, pp. 304-117. doi:10.1111/j.1525-142X.2006.00101.x
Walsh, Denis (2015). Organisms, Agency, and Evolution. Cambridge UK: Cambridge University Press.
Steve Talbott :: Let’s Not Begin With Natural Selection