“Dear Blair, of course you are right, but the scale is all wrong. Predictability of course within a constrained design and clade of close relatives as in your example. My contingency is at the much higher level of designs themselves.”
Blair Hedges recently sent me the image on the left with the following explanation:
“I was preparing a lecture for my evolution class and came across this reply from Steve Gould to me many years ago (Oct 1986), on a post-it note!
I can’t find my original letter to him but I recall it well. As a grad student, I heard him give a lecture about the Cambrian Explosion where he claimed that evolution operated differently –contingency instead of adaptation or predictability– at the higher level of animal designs. I told him I disagreed because I was seeing too much predictability in the adaptive radiations on Caribbean islands to believe that it was not happening throughout life at all levels.
Translation of his reply: “Dear Blair, of course you are right, but the scale is all wrong. Predictability of course within a constrained design and clade of close relatives as in your example. My contingency is at the much higher level of designs themselves.”
Not sure how you feel about it, but I still don’t agree with his explanation! 500 mya the Cambrian explosion was just an adaptive radiation like anoles.”
Interestingly, this story jibes very closely with a story of my own. In 1998, a number of colleagues and I published a paper in Science reporting a phylogenetic analysis of Caribbean anoles demonstrating convergent evolution of the anole ecomorphs. A reporter for Science contacted me and in the ensuing discussion, I suggested that an interesting person to contact to get an opinion of the paper would be Stephen Jay Gould. I was quite disappointed when her piece appeared and had no quote from Gould. When I subsequently talked to her, I was astounded to learn that she had, indeed, talked to Gould and he had given a reply pretty much exactly the same as on the post-it above. And…she had decided no one would be interested in what S.J. Gould had to say about replicated, convergent adaptive radiation, and so she didn’t include the quote in her article.
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Shea Lambert
I’m not sure Blair’s view and Gould’s are irreconcilable. In my interpretation, Gould doesn’t argue that predictable sorts of evolution aren’t always operating, just that when you expand the scale enough (i.e., look at larger amounts of time), they are masked by contingency. So to Blair’s point, given a set of replicate earths, each seeded with the starting material available to evolution 500mya on this earth, we might find a set of Cambrian explosions ‘shortly’ thereafter that aren’t all that different. I’m not sure Gould would disagree there*. But allow for 500 million more years of evolution in each of those replicate earths, and he’d certainly argue that you’d have a hard time predicting the results, in terms of which types of bauplans have been created and which have thrived.
I don’t see how anyone can argue against the idea that, when dealing with a process that involves any stochasticity at all (which evolution clearly does), forecasting the results gets harder when you try to do it over longer periods of time. For what it’s worth, when Gould talked about replaying the tape of life, I’ve always interpreted that as ‘from the beginning’, making his ideas about contingency really not all that relevant to Anolis or any one particular radiation.
*But I suspect this is where my interpretation of Gould’s ideas is most likely to be mislead
Blair Hedges
Glad to see any discussion on this topic because there are still important questions to address by students of evolution.
To fill in a bit of history, by “replaying the tape of life,” Gould (in Wonderful Life) did not mean from the beginning, but rather from the Cambrian. His proposal was that the Cambrian Explosion was an unusual time in the history of life when the branches went in all directions, and then random extinction left a small number of surviving lineages. He did not consider the Cambrian Explosion to be just another adaptive radiation–his whole point was that it was a special, unique time in evolution. He greatly emphasized contingency, as opposed to natural selection, as operating at that time. Scientists gave him a bit of heat for that, and there were some critiques –I recall one in Science where some paleontologists demonstrated that the Cambrian organisms that Gould claimed were in their own separate phyla (supporting contingency) were actually members of known phyla, weakening the contingency argument. (since this is a blog, excuse me for not citing references!). I really enjoyed most of what Gould wrote, and he was a brilliant evolutionary biologist. I just disagreed with him on that point. I think there is some convergence at all levels in the tree of life, and that is often under-appreciated. Just look at a porpoise, shark, ichthyosaur, and marlin, organisms separated by 300-500 my, and yet they exhibit pretty accurate convergence for their pelagic niche. And even further back, the many unrelated vermiform animals, exhibiting an ideal body plan for substrate burrowing. I do think that replaying the tree of life would result in at least some things that we would recognize.
Jim Jackson
If Gould were still with us, even his rhetorical skills would be hard pressed to defend the importance of “contingency” in the face of the numerous instances, at higher taxonomic levels, of convergence in performance. See George McGhee’s compendium of such convergences: Convergent Evolution, Limited Forms Most Beautiful; MIT Press.
Rich Glor
Nice, I haven’t seen that book by McGhee yet. Of course, the subject of Gould’s book Wonderful Life wrote his own account contradicting Gould’s claims about the uniqueness of evolutionary phenomena: Life’s Solution.
Peter Mudde
Well I have to give it to Conway-Morris. Everytime I leaf through my fieldguides it strikes me how much animals from totally different families and on totally different halves of the planet look like carbon copies of each other..
Daniel Scantlebury
But wouldn’t the Caribbean be more impressive if each of the big islands were populated with ecomorphologically equivalent communities of different lizard clades? Anoles for one, skinks for another, etc, all with twig, grass-bush, crown-giant exemplars.
The anoles of the Greater Antilles trace their origins back to a single lineage, and I don’t believe it is unreasonable to suggest the components of the genetic architecture that today give rise to anole ecomorphological diversity were segregating in that single lineage at the time of colonization. So, how independent were the starting conditions for each island if they were each seeded with similar sets of genetic polymorphisms?
Richard Lenski
Very nice post, Jonathan, that adds personal touches to the history of science!
For what it’s worth, I spoke with Gould twice when he visited MSU (once for an honorary degree in 1999, and once for a special lectureship in 2000). On those occasions, Gould was very open to discussing contingency at smaller scales, even in the flasks of my long-term evolution experiment with E. coli. And that openness is, I think, also reflected in his discussions of our work in his last book, The Structure of Evolutionary Theory. So while he was certainly most interested in contingency with respect to deep time, I think he also recognized that it could be studied at multiple scales.
Another amusing anecdote — from memory, so I may not have the details right: Gould was asked to comment for some publication on our 1995 paper on “Experimental tests of the roles of adaptation, chance, and history in evolution” (Travisano, M., J. A. Mongold, A. F. Bennett, and R. E. Lenski. 1995. Science 267:87-90). Gould was quoted as saying something to the effect that he hadn’t read the paper but it sounded possibly interesting. I remember thinking that you’re famous when you can get quoted in a major news outlet for saying you haven’t read something, but maybe it’s interesting!