(Roughly) Daily

Indeed. Scientists have accepted this precept since Charles Darwin‘s publication of Origin of the Species. But how– and at what pace– does that adaptation happen? From those earliest days, the assumption was that change/adaptation happened slowly, roughly evenly– gradually– over time.

But in 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it punctuated equilibria. Their paper built upon Ernst Mayr‘s model of geographic speciation, I. M. Lerner‘s theories of developmental and genetic homeostasis, and their own empirical research. Eldredge and Gould proposed that the degree of gradualism commonly attributed to Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species. Rather, they argued, when significant evolutionary change occurs, it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis (the process by which a species splits into two distinct species, rather than one species gradually transforming into another).

Jake Buhler reports on recent work that confirms the punctuated equilibrium theory and adds more detail…

Over the last half-billion years, squid, octopuses and their kin have evolved much like a fireworks display, with long, anticipatory pauses interspersed with intense, explosive changes. The many-armed diversity of cephalopods is the result of the evolutionary rubber hitting the road right after lineages split into new species, and precious little of their evolution has been the slow accumulation of gradual change.

They aren’t alone. Sudden accelerations spring from the crooks of branches in evolutionary trees, across many scales of life — seemingly wherever there’s a branching system of inherited modifications — in a dynamic not examined in traditional evolutionary models.

That’s the perspective emerging from a new mathematical framework (opens a new tab) published in Proceedings of the Royal Society B that describes the pace of evolutionary change. The new model, part of a roughly 50-year-long reimagining of evolution’s tempo, is rooted in the concept of punctuated equilibrium, which was introduced by the paleontologists Niles Eldredge and Stephen Jay Gould in 1972.

“Species would just sit still in the fossil record for millions of years, and then all of a sudden — bang! — they would turn into something else,” explained Mark Pagel, an evolutionary biologist at the University of Reading in the United Kingdom.

Punctuated equilibrium was initially a controversial proposal. The theory diverged from the dominant, century-long view that evolution adhered to a slow, steady pace of Darwinian gradualism, in which species incrementally and almost imperceptibly developed into new ones. It opened the confounding possibility that there was a discontinuity between the selection processes behind the microevolutionary changes that occur within a population and those driving the long-term, broad-scale changes that take place higher than the species level, known as macroevolution.

In the decades since, researchers have continued to debate these views as they’ve gathered more data: Paleontologists have accumulated fossil datasets tracing macroevolutionary changes in ancient lineages, while molecular biologists have reconstructed microevolution on a more compressed timescale — in DNA and the proteins they encode.

Now there are enough datasets to more fully test the theories of evolutionary change. Recently, a team of scientists blended insights from several evolutionary models with new methods to build a mathematical framework that better captures real evolutionary processes. When the team applied their tools to a selection of evolutionary datasets (including their own data from research into an ancient protein family), they found that evolutionary spikes weren’t just common, but somewhat predictably clustered at the forks in the evolutionary tree.

Their model showed that proteins contort themselves into new iterations more rapidly around the time they diverge from each other. Human languages twist and recast themselves at the bifurcations in their own family tree. Cephalopods’ soft bodies sprout arms and bloom with suckers at these same splits.

The new study adds to previous support for the punctuated equilibrium phenomenon, said Pagel, who wasn’t involved in the project. However, the rapid evolutionary behavior isn’t a unique process separate from natural selection, as Eldredge and Gould suggested, but rather the result of periods of extremely rapid adaptation propelling evolutionary change.

“This is really a rather beautiful story in the philosophy of science,” Pagel said…

Read on for the fascinating story of the updated evolutionary model shows that living systems evolve in a split-and-hit-the-gas dynamic, where new lineages appear in sudden bursts rather than during a long marathon of gradual changes: “The Sudden Surges That Forge Evolutionary Trees,” from @jakebuehler.bsky.social‬ in @quantamagazine.bsky.social‬.

Given the strains that the Antropocene is putting on our environment, this could be timely…

* Charles Darwin

###

As we dissect development, we might spare a thought for Barabara McClintock; she died on this date in 1992. A cytogeneticist, she is regarded as one of the most important figures in the history of genetics. In the 1940s and 50s McClintock’s work on the cytogenetics of maize led her to theorize that genes are transposable – they can move around – on and between chromosomes. McClintock drew this inference by observing changing patterns of coloration in maize kernels over generations of controlled crosses. The idea that genes could move did not seem to fit with what was then known about genes, but improved molecular techniques of the late 1970s and early 1980s allowed other scientists to confirm her discovery. She was awarded the 1983 Nobel Prize in Physiology or Medicine, the first American woman to win an unshared Nobel Prize.

For more on McClintock’s work and its legacy, see here and here.

source