Two days ago I wrote a critique of a new article in the Guardian, an article claiming that the modern theory of evolution is obsolete. To support this claim, author Stephen Buranyi asserted that there are new areas of research—areas like the “neutral theory”, the importance of epigenetics and niche construction, and Gould and Eldredge’s theory of “punctuated equilibrium” that proposed a novel mechanism for a “jerky” fossil record—that have made the modern theory of evolution outdated and, in fact, pretty much obsolete.
Although these ideas were novel and expanded the ambit of evolutionary research, with the neutral theory gaining prominence in the Sixties and punctuated equilibrium in the Seventies and Eighties (culminating with Gould’s big 2002 book, The Structure of Evolutionary Theory), I want to show here that both of these ideas had at least been considered by Darwin.
That is, in the first edition of On the Origin of Species in 1859, Darwin mentioned that some “variations” (he meant what we called “the result of mutations”) could have no effect on survival or reproduction, and therefore whose fate would be determined by the vagaries of chance. This is what the neutral theory, made prominent by Tomoko Ohta and Motoo Kimura, and now by people like Mike Lynch, really asserts, and we have a sophisticated mathematical theory about the fate and effect of neutral mutations.
Further, in The Origin Darwin not only mentions the possibility of a “punctuated” fossil record—in which nothing changes for a long time and then there are bouts of rapid change—but also floats a theory that bears a striking similarity to Gould’s mechanism for that pattern. Mind you, Darwin’s thoughts on these issues were not the inspiration for either the neutral theory or punctuated equilibrium, but they were already in Darwin’s mind before 1859. This shows that there’s nothing totally new under the evolutionary sun, but also how smart Darwin was.
Here’s my beat-up copy of the first edition of The Origin, which I believe I bought in graduate school. As you see, it’s been well read and mended with tape. I still go through the first edition, though in a different physical book, once every few years.
Over the years, as I reread that copy, I noted on the back cover where Darwin had anticipated modern ideas. Here I’ll talk about just two: “neutral characters” and “punctuated equilibrium”. But you see that there are other “modern” ideas that Darwin discussed in 1859, like allopatric speciation and kin selection. If you have this book, which is probably out of print, you can use the page numbers below to see what he said.
So, on to the two topics.
THE NEUTRAL THEORY
Here’s what the Guardian says about neutral theory:
Doolittle and his allies, such as the computational biologist Arlin Stoltzfus, are descendants of the scientists who challenged the modern synthesis from the late 60s onwards by emphasising the importance of randomness and mutation.
And below are two bits from The Origin about variations that are “neutral”, i.e.m “are of no service or disservice to the species” (he means “individual”). I’ve put Darwin’s musing on neutral variations in bold.
Chapter II (2)
There is one point connected with individual differences, which seems to me extremely perplexing: I refer to those genera which have sometimes been called “protean” or “polymorphic,” in which the species present an inordinate amount of variation; and hardly two naturalists can agree which forms to rank as species and which as varieties. We may instance Rubus, Rosa, and Hieracium amongst plants, several genera of insects, and several genera of Brachiopod shells. In most polymorphic genera some of the species have fixed and definite characters. Genera which are polymorphic in one country seem to be, with some few exceptions, polymorphic in other countries, and likewise, judging from Brachiopod shells, at former periods of time. These facts seem to be very perplexing, for they seem to show that this kind of variability is independent of the conditions of life. I am inclined to suspect that we see in these polymorphic genera variations in points of structure which are of no service or disservice to the species, and which consequently have not been seized on and rendered definite by natural selection, as hereafter will be explained.
Chapter IV
HOW will the struggle for existence, discussed too briefly in the last chapter, act in regard to variation? Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature? I think we shall see that it can act most effectually. Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and, in a lesser degree, those under nature, vary; and how strong the hereditary tendency is. Under domestication, it may be truly said that the whole organisation becomes in some degree plastic. Let it be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life. Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some bering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic.
*************
PUNCTUATED EQUILIBRIUM
Here’s what the Guardian article says about punctuated equilibrium:
Other assaults on evolutionary orthodoxy followed. The influential palaeontologists Stephen Jay Gould and Niles Eldredge argued that the fossil record showed evolution often happened in short, concentrated bursts; it didn’t have to be slow and gradual.
But as I emphasized in my critique, Gould and Eldredge’s pattern of a “jerky” fossil record was really supplemented, extended, and publicized by Gould in later writings. The theory got a lot of attention not just because a fossil record of stasis and episodic change (if real and ubiquitous) shows that evolution isn’t as gradual as Darwin or others thought, but because Gould posited a novel, almost non-Darwinian mechanism for that change. If you don’t want to read about this complex mechanism, just skip down to the bold part labeled RESUME READING.
The mechanism, in short, is this. Populations of a species become geographically isolated and thus diverge genetically. (This is the first step of the process of speciation that we call “allopatric speciation”, thought by most to be the main way new species arise.) According to Gould, the divergence isn’t really due to natural selection, but to a process of either neutral or maladaptive variants coming to predominate via genetic drift in different populations. (He also posited that many of these variants are “macromutations”: mutations of very large effect, but we’ll leave that erroneous assumption aside.)
Maladaptive mutations are important because they require, to be “fixed” in a group, a small population as well as very strong genetic drift. Such drift can in fact lead maladaptive mutations to predominate in populations, overcoming natural selection that would normally eliminate them. When these mutations predominate—Gould used the example of “Galton’s polyhedron”, a solid that can be pushed and pushed, and suddenly falls on another face that represents a new species—they can then cause reproductive isolation when the new populations hybridizes with others. That reproductive isolation is the most important aspect of speciation.
This is complicated, but take my word for it.
Finally, the new, small population that has new traits and is reproductively isolated from related populations, simply expands and takes over the whole group, a form of “species selection”. This is not Darwinian “individual or genic selection” because the traits of the expanding population itself (and their underlying genes) are not fitter than the traits of other populations. Instead, the expanding small population has for other reasons either an increased chance of producing new species or a reduced probability of extinction.
This process, said Gould, explains the jerky fossil record. The evolutionary change in the small population isn’t seen in the fossil record because a small population has a small chance of being seen in the fossil record. But when it supplanted all the other populations, it did so rapidly, and that’s why the fossil record is jerky. Most of the time all the populations of a species are changing in different ways, which average out to “no big change overall” seen in fossils, but when the newly isolated population takes over, then we see big change in the fossil record.
I argued with Gould about this in the literature; one problem is that Gould often denied what he’d said before in print, and never specified a unified, coherent mechanism for punctuated change in a single place. (To see one exchange we had in the literature, go here.)
As I said, there are huge problems with this mechanism, as both the “valley crossing” and “species selection” are very unlikely to happen often, much less often enough to explain ubiquitous jerky patterns. Gould’s mechanistic speculations haven’t stood the test of time, and I haven’t heard them discussed for many years in evolutionary biology (for critiques, see here). Further, there are two other and more parsimonious explanations for a jerky fossil record. The first is that the deposition of sediments itself, which is where we can find fossils, is episodic, with some periods of rapid sedimentation alternating with periods of little sediment formation. Even if evolution were continuous and gradual, this would make it look jerky.
Second—and nobody doubts this, either—natural selection itself varies in strength and direction, and that can cause a jerky patten, too. The classic example is the 1977 drought in the Galápagos islands in that caused evolutionary change by actually killing the smaller individuals of the medium ground finch by making them unable to eat big seeds. This form of natural selection, documented by Peter and Rosemary Grant and their colleagues, was the subject of the Pulitzer-Prize-winning book The Beak of the Finch (1994) by Jon Weiner. But after one year the rains came again, the small plants with smaller seeds grew, and finch beak size returned to normal. Here we see an episodic example of natural selection that caused a rapid change (an increase of 10% in beak size in a single generation!) followed by a reversal of that selection.
Even if the fossil record shows an episodic pattern, then, this does not buttress Gould’s convoluted and unlikely mechanism of evolutionary change. People often forget that it is Gould’s novel mechanism, involving macromutations, genetic drift, maladaptive evolution, and species selection, that gave punctuated equilibrium much of its cachet. But evolutionists have no problem with a fossil pattern showing fast evolution during some periods and not much change during others. That does not conflict with the modern theory of evolution.
RESUME READING
I was struck when reading The Origin that Darwin gives not only the “episodic sedimentation” explanation for an uneven fossil record, but also comes close to Gould’s “spread of an isolated population” explanation. Here are two excerpts from the latter part of the book showing this. I’ve put the relevant parts in bold.
Chapter IX
One other consideration is worth notice: with animals and plants that can propagate rapidly and are not highly locomotive, there is reason to suspect, as we have formerly seen, that their varieties are generally at first local; and that such local varieties do not spread widely and supplant their parent-forms until they have been modified and perfected in some considerable degree. According to this view, the chance of discovering in a formation in any one country all the early stages of transition between any two forms, is small, for the successive changes are supposed to have been local or confined to some one spot. Most marine animals have a wide range; and we have seen that with plants it is those which have the widest range, that oftenest present varieties; so that with shells and other marine animals, it is probably those which have had the widest range, far exceeding the limits of the known geological formations of Europe, which have oftenest given rise, first to local varieties and ultimately to new species; and this again would greatly lessen the chance of our being able to trace the stages of transition in any one geological formation.
It should not be forgotten, that at the present day, with perfect specimens for examination, two forms can seldom be connected by intermediate varieties and thus proved to be the same species, until many specimens have been collected from many places; and in the case of fossil species this could rarely be effected by palæontologists. We shall, perhaps, best perceive the improbability of our being enabled to connect species by numerous, fine, intermediate, fossil links, by asking ourselves whether, for instance, geologists at some future period will be able to prove, that our different breeds of cattle, sheep, horses, and dogs have descended from a single stock or from several aboriginal stocks; or, again, whether certain sea-shells inhabiting the shores of North America, which are ranked by some conchologists as distinct species from their European representatives, and by other conchologists as only varieties, are really varieties or are, as it is called, specifically distinct. This could be effected only by the future geologist discovering in a fossil state numerous intermediate gradations; and such success seems to me improbable in the highest degree.
Chapter XIV
Only organic beings of certain classes can be preserved in a fossil condition, at least in any great number. Widely ranging species vary most, and varieties are often at first local,—both causes rendering the discovery of intermediate links less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they do spread, if discovered in a geological formation, they will appear as if suddenly created there, and will be simply classed as new species. Most formations have been intermittent in their accumulation; and their duration, I am inclined to believe, has been shorter than the average duration of specific forms. Successive formations are separated from each other by enormous blank intervals of time; for fossiliferous formations, thick enough to resist future degradation, can be accumulated only where much sediment is deposited on the subsiding bed of the sea. During the alternate periods of elevation and of stationary level the record will be blank. During these latter periods there will probably be more variability in the forms of life; during periods of subsidence, more extinction.
With respect to the absence of fossiliferous formations beneath the lowest Silurian strata, I can only recur to the hypothesis given in the ninth chapter. That the geological record is imperfect all will admit; but that it is imperfect to the degree which I require, few will be inclined to admit. If we look to long enough intervals of time, geology plainly declares that all species have changed; and they have changed in the manner which my theory requires, for they have changed slowly and in a graduated manner. We clearly see this in the fossil remains from consecutive formations invariably being much more closely related to each other, than are the fossils from formations distant from each other in time.
In the last paragraph Darwin hews to the well-known “gradualism”, to which he admitted no exception. The jerky patterns in the fossil record he ascribes to either an incomplete fossil record or to straight natural selection, with the spread throughout a species of adaptive variants arising in isolated populations.
As I said, these musings didn’t have any influence on Kimura or Gould, but they do show that Darwin was already thinking about neutral variations and about a punctuated fossil record well before he published this stuff in 1859.
The breadth and originality of Darwin’s thinking is one reason why everyone should read The Origin, even if its Victorian prose is sometimes daunting. (The chapter on “hybridism”, for example, is a real slog.) But I hope I don’t sound pretentious if I say that a person cannot be considered properly educated if they haven’t read Darwin’s great work—ideally the first edition so you can get a full flavor of how revolutionary it was.
Amen.
Sub
One generation passeth away, and another generation cometh: but the ToE abideth for ever.
(I mean, as long as you goin’ with Ecclesiastes 1, why not?)
On a similar theme, regarding puncutated equilibrium (periods of stasis along with episodes of faster change), here is Huxley writing in 1876:
“It is obvious that, if it can be proved that animals have endured, without undergoing any demonstrable change of structure … no form of the hypothesis of evolution which assumes that animals undergo a constant and necessary progressive change can be tenable … But it is no less plain that if the process of evolution of animals is not independent of surrounding conditions; if it may be indefinitely hastened or retarded by variations in these conditions”, […]
“There are groups of reptiles … [that] throughout the whole of the great series of Mesozoic rocks, they present no such modifications as can safely be considered evidence of progressive modification. Facts of this kind are undoubtedly fatal to any form of the doctrine of evolution which postulates the supposition that there is an intrinsic necessity, on the part of animal forms which have once come into existence, to undergo continual modification; and they are as distinctly opposed to any view which involves the belief, that such modification may occur, must take place, at the same rate, in all the different types of animal or vegetable life. […]
“But the important point is that, granting the existence of the tendency to the production of variations; then, whether the variations which are produced shall survive and supplant the parent, or whether the parent form shall survive and supplant the variations, is a matter which depends entirely on those conditions which give rise to the struggle for existence. If the surrounding conditions are such that the parent form is more competent to deal with them, and flourish in them than the derived forms, then, in the struggle for existence, the parent form will maintain itself and the derived forms will be exterminated. But if, on the contrary, the conditions are such as to be more favourable to a derived than to the parent form, the parent form will be extirpated and the derived form will take its place. In the first case, there will be no progression, no change of structure, through any imaginable series of ages; in the second place there will be modification of change and form.”
It seems that a jerky fossil record is intuitively likely under a darwinian evolutionary mechanism in any case. In periods of environmental stasis species will tend to be well adapted to their environment and it will be hard for new forms to invade. Conversely in periods of rapid change either globally or regionally (climate change, comet strikes, increased volcanic activity etc) the disruption will increase the likelihood of established species going extinct whilst simultaneously creating new opportunities for adaptive radiation and speciation. This would give rise to a fossil record that showed periodic bursts of change. [An amateur speculation that I will be happy to have corrected if I have got it wrong…].
Jerry tells us what Darwin said, Coel what Huxley said – I rather thank someone needs to tells us what Wallace said! 😉
these musings didn’t have any influence on Kimura or Gould, – How can we be sure about that? They must have been intimately familiar with the book. It may be that it was inspirational to them but perhaps they didn’t admit it.
Well I’m just guessing here–I admit that. But I don’t remember anybody ever citing Darwin. If someone did, it would Gould on pun. eq. Check the index of his big book under “Darwin”.
For what it’s worth, I remember that in the end Kimura – the great champion of ‘neutral mutations’- reluctantly, very reluctantly, admitted that natural selection played an important role in evolution.
How could it not? How could you get adaptation without natural selection?
Ask Motoo Kimura, I don’t know if it is apocryphal, but apparently he could not make the statement (that natural selection of beneficial mutations was the greater driver of evolution) himself, but delegated it to one of his students.
In Kimura’s defense, that question requires a lot of context. Evolution of what?
If we are talking about molecular evolution, then neutral drift is the dominant mechanism, at least in the case of complex eukaryotes with junky genomes. The vast majority of change in the DNA sequence of these genomes is neutral mutations.
If we are talking about morphological change, how do we quantify the relative contribution of fixed deleterious changes, neutral changes, and beneficial changes? Is an attached ear lobe more beneficial than a detached ear lobe? Is there just one shape of a nose that is beneficial, or are changes to nose shape largely neutral?
Is natural selection an important mechanism for understanding the evolution of species? Absolutely. However, much like biology itself, evolution is a very complex process that carries a lot of nuance.
Okay, you’ll be glad to know that I read all that, and understood it, and I appreciated it!
But tangentially, at the bottom of your notations on your copy of The Origin you wrote “Greater productivity with greater diversity” — which is an intriguing remark. Care to expand on that?
That, Peter, was written so long ago that I can’t remember. It may be Darwin’s view that species expand their niches (leading to sympatric speciation) because it allows for greater productivity by taking advantage of unused environment.
Looks like you missed some text in the chapter 4 quote – you have “Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some
[missing a line here]
bering that many more individuals are born than can possibly survive)”
the missing line is
“way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remem-”
http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=1
See – I was paying attention!
😉
I vaguely recall Darwin doing experiments or making observations to see if rich (“productive”) habitats would be more diverse than poor ones.
I think this is still a field of investigation today. The answer is often “No”.
There has been a reasonable amount of work in the last few decades, though more often under the flag of “ecological studies” than “evolutionary studies”, studying the efficiency of resource use, and the robustness of ecological networks in ecologies with more, or fewer genera of organisms. Which is certainly in the direction of Jerry’s (unsuccessful) aide memoire.
Empirically, one can readily conceive that an ecosystem with three genera (#1, #2, #3) harvesting energy from the environment and producing “wastes” and unusable “waste heat”, may well have “room” a 4th genus to invade the system and devour the energy in (say) organism #2’s waste products, while producing a waste which organism #3 can use. (In the real world it is more likely that #4’s invasion of the habitat, will lead to the linked invasion of #5, #6, and #7 which have elsewhere evolved eating #4’s waste. Eventually, the around 2eV (wavelength dependent) of energy from each incoming photon hitting chlorophyll will get sliced and diced into waste heat at a fraction of an eV per photon, in a chain of organisms.
Once you start thinking about energy and thermodynamics, it becomes hard to not think that way.
Putting that into perspective, the thermodynamics of steam engines was being developed as Darwin sat in Devonport on the Beagle, throwing up, regretting his choices, and wishing someone would find something better than wind for propelling ships. “Ecology” as a way of thinking about the interrelationships of populations of organisms didn’t formalise until the 1920s. And the link between photon energy and wavelength earned a Nobel gong for one A. Einstein in 1920. So it’s not surprising that the hints of it were very distant in the 1840s writings of a geologist. But to a grad student looking from the early 1960s with all the hindsight that entails, rather clearer.
Darwin’s comment on the improbability of future geologists being able to prove from fossils that todays breeds of horses, cattle, dogs etc arose from common stock is a great point which scotches what many a creationist thinks is a gotcha when they point to the rarity of intermediate forms.
Well, maybe not geologists, but geneticists certainly did. But then, Darwin did not know about genetics.
Yes I appreciate the point applies to fossil evidence only and not to genetic evidence. But the creationist assertion that the lack of intermediate forms in the fossil record is a problem for proponents of evolution is well addressed by Darwin’s point. Of course we are also aware of good examples of intermediate forms in various lineages anyway.
Yeah, in Darwin’s time the only ‘intermediate’ form recognised as such was the Archeopterix, but I don’t think Darwin ever seized on that (AFAIK).
Forgive me – Archaeopteryx !
🙂 xxx
Sorry !!!
Thanks for correcting me, I indeed meant Archaeopteryx .
There is evidence other than genetic and fossil evidence. in 1882, George Romanes wrote of several lines of evidence in his essay “The Scientific Evidences of Organic Evolution” that weren’t genetic or fossil evidence. For example, the classification of life is tree like, and that includes the group that houses mammals. There is also his argument from morphology where he talks about common features that were modified in different branches (e.g. the tetrapod forelimb). He also talked about the evidence from biogeography and embryology.
Very true, he definitely did base his theory on much more than fossils. Apart from the fields you mention, in his “The Expression of the Emotions in Man and Animals” he even used comparative psychology to stress common descent.
I think that Wallace’s evidence to come to the same conclusion as Darwin was mainly biogeographical, not geological or paleontological.
For reference, Darwin largely thought of himself as a geologist, not as a biologist. He was Secretary of the Geological Society for several years in the early 1840s until a combination of moving to Kent and probably ill health led to him standing down from the position.
I’m not sure when he was elected to Fellowship of the Linnean, today the Geol.Soc’s neighbour under the arch at Burlington House. Would it have been after the barnacles?
Darwin was amazing. Every time I taught my graduate seminar, The Fossil Record of Evolution, we started the course by reading and then discussing Darwin’s Origin of Species (first edition). Every time I read it I learned more. In the intervening year, I became better versed in my own subject of paleontology, so every time I read the Origin I read it from a different perspective. Its richness goes on and on. The same goes for Darwin’s many other writings, which are considerable, but the Origin is extraordinary.
Since Jerry included some commentary on Steve Gould, let me make a few comments as well. I was a graduate student of Gould’s during the time period at issue. In my view, Steve did a lot to muddy the waters around punctuated equilibria. He and Niles Eldredge *could* have interpreted the observed paleontological pattern as being well within the confines of the modern synthesis, with the geologically rapid changes observed in the fossil record being an expected outcome of Ernst Mayr’s allopatric speciation followed by expansion of the new species across the old species’ range. And Eldredge did seem to hold to this position when he published his original work on Phacopid trilobites. (I never discussed this with Eldredge directly but infer it from his articles.)
It was Gould who seemed to want to push the boundaries into new territory. A good deal of this was less new than it seemed and, as Jerry writes, was indeed anticipated by Darwin himself. Gould (with Dick Lewontin in their “spandrels” paper) reminded us of the role played by historical and structural constraints, of the role of nonpredictability in evolution, and (with Dave Raup and others) of the role of mass extinction events in altering the composition of the biota, but Steve was inclined explicitly or implicitly to characterize these phenomena as somehow non-Darwinian. I don’t want to misrepresent a scientist who is gone and can no longer respond but for reasons only Gould could know, Steve seemed compelled by personality to radicalize his findings whether it was called for by the evidence or not.
Interesting (at least to me) is that much of the hubbub was sustained by Gould’s prolific writing and his rhetorical skills. Now that Gould is no longer with us, his corpus of work can be judged by contemporary biologists and by history.
In Gould’s defence, despite all his prevarications (punctuation, spandrels, hopeful monsters, etc,) he never questioned that natural selection was the great mover of evolution. At least, that is what I got from his writings.
Gould was a firm believer that natural selection was responsible for adaptation, particularly what he called the fine-tuning of organism and environment. You’re quite right about that. For other observations—such as (frequent, but not universal) long-term increases in body size, changing proportions of species numbers in clades, the origin and maintenance of morphological gaps between major body plans (Baupläne), and other sorts of phenomena gleaned from the fossil record, he tended away from adaptationist explanations. He also believed that in the geological long run, these phenomena deserved more attention.
Interestingly, many of the paleontological phenomena that Gould wrote about (assuming that they are real and not artifacts of a spotty geological record) have a long history that predates the synthesis, and one of the outcomes of the modern synthesis was to reconcile (at least some of) these phenomena with the rest of Neodarwinism. George Gaylord Simpson took the lead in this endeavor with his 1944 book. Gould was never satisfied with this reconciliation and doubted that mutation and selection were enough to explain several important aspects of the long term history of life. If we accept that there are evolutionary phenomena that require explanations other than mutation and selection—such as the extinction of the dinosaurs during an asteroid collision—do we really need a new evolutionary synthesis? I have my opinion but will leave that to those who are currently active in the field.
I suppose our obvious problem is that we can only glimpse short term evolutionary changes in contemporary species, or long term changes in the spotty fossil record, & I think that is why evolutionary biologists & palaeontologists view evolution in different ways, or at least have done in the past. We do not have the luxury of being able to observe evolution over a long period of time except by extrapolating the one, & trying to fill the gaps in the other. Genetics only tells us how mostly recent genomes differ & we then try to link that with the other two. I do not see this problem as solvable as we are unlikely to be around as a species in 100,000 years to take stock! I also suppose the Wiener book only shows the drives of selection that could form a species, given a fixed change in the envirionment that might possibly eliminate the genetic potential fore small beaks. It was not a speciation is what I mean & we would not expect it to be i suppose unless you were a saltationist?
Apologies Jerry, I missed the critique of the Grauniad article (& the article itself). Will attempt to go back & do my homework…
Well, you might be right, but I must say, living in the MCZ with Gould, hearing him talk, and reading nearly everything he wrote (except bout snails), I’d be hard pressed to find an explicit admission by Gould of the power of natural selection. He was an anti-adaptationist (remember the Spandrels paper!), and if he extolled the power of natural selection as “the great mover of evolution” that idea didn’t come across to me.
Steve was all over the map and hard to pin down. I could probably find some quotations where he’s explicit about the important role of selection, but I’d have go to the library as I don’t have access anymore to the literature. Here’s how I would characterize him.
—Gould believed that natural selection is largely responsible for the fine-tuning of organisms in populations to their environment and for keeping populations in tune over time.
—Gould was less accepting of the power of natural selection when it came to the origin and “improvement” of biological traits. His book on the Burgess Shale is interesting, for example, in that he struggles to explain the burst of evolutionary change at the base of the Cambrian under the conventional rubric of mutation and selection. To him, the scope of the differences among those amazing creatures of the Cambrian and how quickly they evolved were problems that needed further exploration—which of course is why he wrote the book.
—He was anti-adaptationist in the sense that he was skeptical of the “just so” stories that are often found in the literature—adaptationist tales that are ad hoc and untested but that sometimes become entrenched simply because they are plausible. As a result, he sought to illustrate (as with Dick Lewontin in the spandrels paper) how phenomena other than natural selection are also important in the fashioning of traits. Since spandrels are necessary architectural elements of domed buildings, the spandrels themselves aren’t adaptations, they argued, but are there by architectural necessity. Adornments added to the spandrels are adaptations since they were adapted (by humans in this case) to the triangular spaces provided by the spandrels. Saying that Gould was anti-adaptationist with a capital A would be going too far. His personality and style led him to emphasize the role of architectural constraints as something that requires more recognition. But he didn’t deny the importance of natural selection in adaptation (at least while I was in the field—up to about 1996).
—Regarding his beloved Cerion (his snails), Steve was amazed about how much variability in these land snails can simply be explained by allometry—that is, by scaling effects associated with body size. If I remember correctly without going back to the literature, research on these snails led him to conclude that much of the local variation in shell shapes he found was non-adaptive. (Shell *size* might be selected for but since shell shape is determined by shell size, he did not see the shape differences themselves as being adaptations.) The fact that some characteristics may be neutral, of course, does not mean that we need a new modern synthesis. After all, as you wrote earlier today, Darwin himself anticipated neutral traits. No new evolutionary synthesis needed here, but Steve was an iconoclast of sorts who tended to emphasize how his discoveries contrasted with received wisdom rather than how they fit in. It’s just how he rolled.
In short (my apologies since this is already too long), Steve was complex. He was a huge admirer of Darwin and sang Darwin’s praises throughout his entire professional life. He was also a strong booster of paleontology and envisioned a paleontology that didn’t merely reflect known evolutionary principles (e.g., mutation and selection) but that contributed to evolutionary theory in its own right. He went too far (in my view) in advocating alternative mechanisms of evolution, and his prolific writing and powerful rhetoric carried some ideas further than they should have gone. Someday someone will write a book that disentangles all of this. I just hope that it’s a shorter book than Gould’s Structure of Evolutionary Theory.
For those thinking “I know that name!”, it’s probably in consequence of a series of reviews Raup produced with Sepkowski of the extinction rates of genera and families in the Phanerozoic fossil record, which laid the footings for the concept of a “mass extinction”. Geologists had, of course, long noted the sporadic turnover of fauna through time (how many of us can remember being told that trilobites disappeared from the fauna “at the end of the Palaeozoic”, having to memorise the changes of brachiopod types at various times within the Palaeozoic, or even the extinction of non-avian dinosaurs at the end of the Cretaceous.
Raup & Sepkowski’s work clarified that the “traditional” dividing lines in the dates of the fossil record largely correspond to major, or even “mass” extinctions. Which is well and good at that level. However they themselves (and a lot of others) have tried possibly over interpreting their results as evidence for periodic recurrences of mass extinctions, and thereby Niburu, Nemesis or a whole flotilla of other long period cosmic events, raining death from the skies onto innocent trilobites and dinosaurs. Which is … not impossible (there’s a suspicious spike of micrometeoroids in the late Ordovician limestones of the Baltic Shield, for example), but the statistical support isn’t strong, and with Raup & Sepkowski’s periodic revisions of their catalogues of extinction, the apparent return period of the celestial executioner changes with each edition of the catalogue. That over interpretation of Raup & Sepkowski’s work isn’t their fault, but since it is very popular with the doom’n’gloom TV programme community, that’s likely where you’ve heard the name before.
I recommend using Jim Costa’s Annotated Origin of Species if reading it for the first time. On one page is Darwin’s original text and on the facing page Jim’s comments on interpreting what Darwin meant.
Yes, how stupid of me not to have thought of that! Costa’s edition is superb and a first-time reader of The Origin should use that one. Thanks, Howie!
Oh I see what you did there! Huxley!
Thanks Jerry for this interesting post.