All mass extinctions in Earth’s history share a common feature: the environment changed faster than life could adapt to it. This idea, in various forms, has been around for several decades, but it had never been tested on a global scale, across the entire history of the animal kingdom and geological time periods.
A new theoretical model, developed at the Massachusetts Institute of Technology and the University of Leicester, has done exactly that, and the findings hold up. The results of the study were published in the journal Physical Review Letters.
The rate at which living organisms adapt, compared with the pace of environmental change, predicts the scale of mass extinctions with striking accuracy. The researchers cautiously note that current rates of change in the carbon cycle are approaching the threshold where adaptation begins to falter.
The study was led by Daniel Rothman, a professor of geophysics and co-director of the Lorenz Center at MIT, and Sergei Petrovskii, a professor of applied mathematics at the University of Leicester.
The team developed a mathematical model for the so-called mismatch rate hypothesis—the idea that extinction occurs when environmental changes outpace evolutionary adaptation—and tested it against geological and paleontological data spanning the last 450 million years.
The intellectual origins of this work trace back to the 18th century, when French naturalist Georges Cuvier, widely regarded as the founder of paleontology, suggested that species could vanish entirely, wiped out by large-scale ecological catastrophes. Eventually, the concept of catastrophism gave way to a view of Earth’s history shaped by slow, gradual processes.
However, in the mid-20th century, American geologist Norman Newell revived the core idea in a more refined form: extinction occurs when environmental changes happen faster than a species can evolve to adapt.
Since then, biologists have documented that this mismatch in rates also manifests at the level of individual species.
The question Rothman and Petrovskii sought to answer was whether the same logic applies on the scale of global mass extinctions—not just individual species struggling with local changes, but the widespread collapse of entire branches of the tree of life.
“We know that individual species go extinct when environmental change outpaces their ability to adapt,” Rothman said. “But until now, it wasn’t clear whether this idea holds for global extinction events.”
The challenge is that the adaptation rates of different animal groups over geological time scales cannot be directly observed. No one has watched a genetic lineage evolve over a million years and measured how quickly it responded to climate change.
Rothman and Petrovskii bypassed this issue by constructing a mathematical description of adaptation rates from first principles.
Successful evolutionary adaptation requires many conditions to be met simultaneously: heritable variation, differential fitness, and a reproductive advantage for better-adapted individuals.
The probability of each condition being fulfilled multiplies, and this mathematical structure produces a characteristic bell-shaped curve: most animal groups adapt at an average rate, while a smaller number adapt very slowly or very quickly.
Having established this general curve, the researchers compared it with data on environmental changes across 27 periods over the last 450 million years, during which the global carbon cycle experienced significant disruptions.
They then analyzed the proportion of animal groups that went extinct in each of these periods, using data compiled by paleobiologist John Alroy.
The model worked. For nearly every major mass extinction in the dataset, there was a measurable mismatch between the rate of environmental change and the rate at which life could adapt. The greater the mismatch, the more species went extinct. The scale of extinctions could be predicted based on the rate of change.
The Permian extinction, which occurred 252 million years ago, was the most severe in Earth’s history, wiping out over 80 percent of marine species.
According to the model, rapid ocean acidification outpaced organisms’ ability to develop adequate physiological defenses. Such events require both a rapidly changing environment and a significant proportion of species whose adaptation rates fall below what those changes demand.
The bell-shaped curve of adaptation rates shows that most animal groups cluster in the middle of the range, meaning they can handle moderate rates of change but not rapid ones.
One of the most striking findings of the study is that the range of adaptation rates across different animal groups broadly matches the range of natural environmental change rates. This coincidence is not accidental.
“We are beginning to observe a certain level of organization and ways life functions that correspond to how the environment functions,” Rothman said. “Life may have evolved so that its range of adaptive abilities matches the range of stresses it encounters.”
In other words, life has not simply reacted passively to environmental changes—over long stretches of time, it may have adapted to the pace of the world it inhabits. This makes it particularly vulnerable when the rate of change exceeds what it was built for.
The researchers carefully weigh how directly to apply this concept to the current situation. But Rothman does not entirely avoid it.
“The level of carbon dioxide in the ocean is rising today at a rate that, when properly scaled, is comparable to rates of carbon cycle change that were only slightly below those seen in major mass extinctions of the past,” he concluded. “This suggests that current rates of environmental change may be approaching those at which adaptation becomes increasingly difficult.”
About the Author
