Punctuated equilibria is not saltationism.

If I get more time, I may weigh in on the debate that has erupted of late on several blogs, namely regarding saltationism in evolution. This was sparked by Olivia Judson’s post, and fanned by Jerry Coyne’s guest critique on Carl Zimmer’s blog, The Loom.

For the moment, I will sidestep the issue of small mutations of large effect (and the additional issue of large mutations, like genome duplications) and will focus briefly on the claim that Coyne makes in the post and in various articles that Eldredge and Gould’s idea of punctuated equilibria is, or at least was, saltationist in mechanism.

It isn’t. It never was. Gould did maintain an interest in macromutations in his discussion of development in the 1970s and 80s, but this was separate from punk eek. Linking them just because the same author discussed them would be like calling natural selection a Lamarckian theory because Darwin considered the inheritance of acquired characteristics in the Origin.

I am pleased to note that Niles Eldredge will provide an article entitled “The early evolution of punctuated equilibria” as his Editor’s Corner of the forthcoming issue of Evolution: Education and Outreach, so look for that in the spring and for additional discussions in future issues of the journal.

You can also consult Gould’s The Structure of Evolutionary Theory, or the chapter on the topic that was published alone as Punctuated Equilibrium.

Meanwhile, I will simply direct you to the summary of punctuated equilbria by Bruce Lieberman and Niles Eldredge at Scholarpedia:

Punctuated equilibria actually comprises several different and related observations. These include:
  1. the fossil record contains a rich source of data useful for developing important evolutionary hypotheses;
  2. speciation typically happens allopatrically, in narrow and geographically restricted populations containing relatively few individuals;
  3. species are not slowly and gradually adapting and evolving over long stretches of geological time;
  4. species lineages that show stasis – or an absence of morphological change – dominate the fossil record and provide useful information about the tempo and mode of evolution;
  5. the first appearance of a new species in the fossil record usually does not represent its point of evolutionary origin but rather the migration of a new geographically isolated species back into its ancestral range, with concomitant expansion in abundance; and
  6. speciation typically takes on the order of 5,000 to 50,000 years to occur – far shorter than the average duration of species in the fossil record.

This is, in essence, an extrapolation into deep evolutionary time, of Ernst Mayr’s ideas regarding allopatric speciation. Mayr himself thought so:

I believe I was the first author to develop a detailed model of the connection between speciation, evolutionary rates, and macroevolution (Mayr, 1954). Although long ignored, my new theory of the importance of peripatric speciation in macroevolution is now widely recognized. “Mayr’s hypothesis of peripheral isolates and genetic revolution must of necessity be a centerpiece of the punctuated equilibria theory; it is the theory, for all practical purposes” (Levinton, 1983:113). I once more presented my theory in great detail (Mayr, 1963:527-555). Under these circumstances it is most curious that the theory was completely ignored by paleontologists until brought to light by Eldredge and Gould (1972).

Mayr, E. 1992. Speciational evolution or punctuated equilibria. In: The Dynamics of Evolution (eds. A. Somit and S.A. Peterson), pp. 21-53. Cornell University Press, Ithaca, NY.

Indeed, here is what he said in the 1954 paper:

…rapidly evolving peripherally isolated populations may be the place of origin of many evolutionary novelties. Their isolation and comparatively small size may explain phenomena of rapid evolution and lack of documentation in the fossil record, hitherto puzzling to the palaeontologist.

Mayr, E. 1954. Change of genetic environment and evolution. In: Evolution as a Process (eds. J.S. Huxley A.C. Hardy, and E.B. Ford), pp. 157-180. George Allen & Unwin, London.

Several bloggers have discussed Coyne’s critique, and you can find summaries here and here. The one to which I most enthusiastically direct you is by Larry Moran. Larry puts it clearly, and points out that even one of Gould’s major detractors agreed that Gould never proposed punctuated equilibria as a saltationist process. Incidentally, I am not the only person to endorse that post. As Niles Eldredge told me when I mentioned the blog discussions, “PS: Larry Moran says it all!”.


2 comments to Punctuated equilibria is not saltationism.

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