Celebrating the 50th Anniversary of the Theory of Punctuated Equilibria

Earlier this week, I had the great honor of joining an incredible group of scientists at the Geological Society of America’s annual meeting in Denver to celebrate the 50th anniversary of the theory of Punctuated Equilibria, published by Niles Eldredge and Stephen Jay Gould in 1972. The meeting was organized by former students of Eldredge and Gould and was a wholly fitting way to celebrate the paper’s semicentennial. Being a neuroscientist and biomedical researcher (essentially a foreigner in an alien paleontological land), I had the opportunity to learn a great deal from these brilliant and dedicated people and appreciated the way they took me under their proverbial wings.

Niles Eldredge (left) and Stephen Jay Gould (right).

We had the opportunity to hear Dr. Eldredge relive some of the history of Punctuated Equilibria (fondly referred to as “punkeek” or “punceq” by those more familiar), as well as many other excellent lectures, ranging from classic paleontology to the philosophy of science. In short, let me summarize by saying that, despite that Punkeek has somehow been perversely equated by Modern Synthesists as “anti-Darwin,” the fossil record just doesn’t support the concept of gradualism as the primary pattern. Nor is it necessary for Natural Selection. Organisms tend to evolve most notably over comparatively short periods of time, followed by prolonged periods of inconsequential (non-directional) change. That is the essence of Punkeek.

Me and Niles Eldredge

Being a relative outsider to this established field, I was perhaps most surprised to find that the theory– in spite of what I would consider overwhelming evidence– is still somewhat controversial. As some noted in their lectures, modern biologists often pay lip service to the theory but don’t tend to integrate it much into their evolutionary framework. Therefore, this problem is rooted not just in the mindset of professionals studying evolutionary biology, but is probably being perpetuated to new generations of students. Surprisingly, the concept of phyletic gradualism– the slow addition of relatively constant, directional change– continues to maintain a conceptual stranglehold.

I do want to make an additional comment here coming from a non-paleontological background: In clinical genetics, we see Goldschmidt’s “hopeful monsters” in action daily. (Not referring to the patients but to the sometimes dramatic changes we see in their genomes.) Genetic variation is not just single nucleotide polymorphisms (SNP) as seem to be the obsession of population geneticists. Instead, many human conditions are rooted in large genomic rearrangements, such as duplications, deletions, translocations, and inversions. What’s more, every 1:2-3 human zygotes is miscarried as the result of major genomic rearrangements. These things are common.

What’s more, the animalian genome is littered with a history of transposable element radiations and major genomic rearrangements– including whole genome duplications! And yet modern detractors of Punkeek, such as Jerry Coyne, continue to claim that there is no evidence of such “macromutations.” I’m not sure what genomes these detractors have been studying, but it doesn’t appear to be any on planet earth. Living genomes are littered with such evidence. This is the norm, not the exception.

I digress. However, these digressions are at the root of the keynote address I gave last Monday afternoon, discussing our Developmental Gene Hypothesis and providing additional data to support its use as a major molecular mechanism underlying Punkeek. Unfortunately, I can’t divulge everything I presented since I’m in the middle of writing up the paper! But suffice it to say that I presented evidence showing that developmental genes in the genome are likely a major genetic factor underlying the “stasis” that Eldredge and Gould noted so many years ago, due in large part to their extreme conservation and mutation intolerance across animals. Paired with a relatively stable abiotic environment, these mechanisms put the brakes on directional shifts in animal form until destabilizing factors arise that shift that balance.

Before I finish this blog, I want to leave you with some information provided by Dr. Peg Yacobucci, Professor of Geology at Bowling Green State University, summarizing the important teaching points surrounding Punkeek. Since Punkeek is probably the “best poorly known” evolutionary theory, misconceptions abound. Therefore, I encourage you to share these snippets with your colleagues, students, and friends.

Here are four major take-home messages:

  • Most morphological (physical) change in a species happens during the speciation process.
  • The speciation process is typically completed within the first 1-10% of a species’ total stratigraphic range within the fossil record.
  • Otherwise, species show little to no net morphological change (i.e., stasis) through most of their stratigraphic range.
  • Punkeek implies that species are evolutionary individuals (unique!) with a defined birth or beginning, character suite, and death or end date.

And with that, I’ll leave you with a picture of the synapsid, Dimetrodon, and the amphibious Eryops, courtesy of the Denver Museum of Nature and Science. Enjoy!

Dimetrodon (left) and Eryops (right).

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