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"Punk Eek," 40 Years Later

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A close-up of a Phacops rana milleri trilobite, showing its compound eye. Courtesy of Flickr/Striving to a goal. 

In the late 1960s, Curator Emeritus Niles Eldredge was a graduate student with a passion for trilobite eyes. He had been taught to expect slow and steady change between the specimens of these Devonian arthropods he collected for his dissertation. Only his trilobites were doing one of two things: staying the same, or evolving in leaps.

Several years later, Eldredge turned his observations into a theory known as “punctuated equilibria”: the idea that species stay relatively the same, or at equilibrium, throughout the fossil record save for rare bursts of evolutionary change. This year marks the 40th anniversary of the landmark 1972 paper on the theory, Punctuated Equilibria: An Alternative to Phyletic Gradualism, which Eldredge wrote with the late Stephen Jay Gould, a noted evolutionary biologist who also served as the Museum’s Frederick P. Rose Honorary Curator in Invertebrates starting in the early 1990s.

The theory was over a century in the making. In On the Origin of Species, Charles Darwin argued that species evolve slowly and gradually. With this view of evolution’s pace, he was haunted by how spotty the fossil record seemed, with its many “missing links” and lack of soft transitions between species.

Eldredge and Gould disagreed with Darwin on this point, arguing that many of the fossil record’s “gaps” reveal how evolution really works.

“The fossil record is a lot better than what people give it credit for,” says Eldredge. According to “punk eek,” as the theory came to be nicknamed, species evolve when small groups of organisms are separated from the main population by something as vast as an ocean or as simple as a river. Geographically and reproductively cut off, this fringe group evolves rapidly, and if it migrates back to its ancestral range, it will look dramatically different and appear as a “jump” in the fossil record.

Eldredge and Gould were the first to show that stasis, not continuous change, is the rule of the fossil record. (Another of their innovations was applying allopatric speciation, a theory on how species evolve in geographic isolation developed by Museum Curator Ernst Mayr and Theodosius Dobzhansky, to paleontology.)

“A lot has been added to the theory since then,” says Eldredge. “Molecular research is independently corroborating it by showing that significant genetic change occurs at the point where species diverge from each other. And we’re now talking about entire faunas and biotas, not just single lineages the way we did in the original paper.”

The theory may have particular import in an age when species’ habitats are radically altering. Historically, extinction events have ushered in dramatic evolution, since rapid change can take place within newly isolated groups of animals. More time will be needed to see if the so-called sixth mass extinction, the ongoing loss of countless modern species worldwide, could lead to the emergence of new organisms.

“It’s far too soon to tell,” says Eldredge, “but there’s lots of genetic divergence out there in response to human alteration of the environment. However, evolution usually kicks in when the vector causing extinction, such as a meteorite, goes away. And right now, that’s us. We’re unlikely to see much recovery while the extinction event is in midstream.”

Eldredge and Gould, who died 10 years ago this month, met as graduate students at Columbia University and would attend seminars together at the Museum, riding the bus back to Columbia and heatedly discussing paleontology and evolution along the way.

Those early bus rides and their collaboration on “punk eek” evolved into a lifelong working relationship. In fact, it was Eldredge who recommended Gould as a columnist for Natural History magazine, which was then published by the Museum. Gould’s columns gained a large following and were subsequently collected in books of popular science.