When an animal’s surroundings transform more rapidly than it can adjust, its survival odds can plummet. This holds true for populations and entire species. Researchers from MIT and the University of Leicester have discovered that this link between evolutionary adaptation and environmental change speed is applicable on a global scale, influencing the likelihood of mass extinction. They introduced a theoretical model of this phenomenon in a paper published in Physical Review Letters.
The team compared their model with data from historical mass extinctions, examining how quickly the global environment shifted during each event. The model accurately forecasted the severity of most mass extinctions throughout Earth’s history, predicting the proportion of life that failed to adapt and thus went extinct. The researchers noted that the adaptation rates across animal groups are generally similar to the rates at which environmental changes occur.
“What we’re beginning to see is a certain level of organization, and ways in which life behaves that are consistent with the ways in which the environment behaves,” says Daniel Rothman, a study author and MIT geophysics professor. He suggests that life may have evolved to match its adaptability range with the range of environmental stresses it encounters. Sergei Petrovskii, a professor of applied mathematics at the University of Leicester, co-authored the study.
The connection between extinction and environmental change isn’t new. In the late 18th century, Georges Cuvier, a French naturalist, first proposed “catastrophism.” After finding fossil bones near Paris that didn’t match any known animal, Cuvier concluded they belonged to an extinct group of giant mammals, likely wiped out by a catastrophe. “That itself was a major idea, that a species could go extinct,” Rothman states, suggesting it was an environmental catastrophe that caused it.
Over time, the concept of catastrophism was replaced by the idea that Earth’s history was mostly shaped by slow processes. In the mid-20th century, American geologist Norman Newell revisited extinction causes, proposing the “rate-mismatch” hypothesis. This idea suggests that extinction happens when environmental change outpaces a species’ ability to evolve. Biologists have observed this hypothesis in action with individual species’ extinctions, leading Rothman and Petrovskii to wonder if it applies globally.
Rothman notes, “We know that individual species go extinct when environmental change outpaces their ability to adapt,” but it remained unclear if this applied to global extinction events. The researchers aimed to test the rate mismatch hypothesis on a global scale, examining whether mass extinction events could be attributed to a mismatch between global environmental change rates and life’s adaptability.
To test this, they needed to compare historical rates of global environmental change and adaptation rates among organisms. Geological records provide data on Earth’s climate changes over time, but adaptation rates are difficult to document. “We’re talking about the rates at which organisms adapt to major environmental change at effectively geologic timescales, from thousands to millions of years,” Rothman explains. Direct observation is not feasible.
Instead, the researchers developed a general mathematical theory to depict adaptation rates across animal groups globally. “Adaptation” here refers to changes within a species over extended periods that enable it to survive environmental changes. Evolutionary theory suggests successful adaptation requires multiple conditions, including population variation, heritable traits, and better adaptation leading to more offspring. If all conditions are met, a species should adapt; if not, it faces extinction.
Rothman and Petrovskii realized that a species’ adaptation success probability multiplies with each met condition, forming a bell-shaped curve. This curve illustrates the fraction of animals adapting at varying rates, with most adapting at intermediate rates and fewer at the extremes. They then compared this pattern to historical environmental change rates during mass extinctions.
Using paleontological and geochemical data from 27 episodes over 450 million years, they analyzed significant carbon cycle changes as indicators of global environmental change. By comparing environmental change rates with animal group extinctions, as established in a study by paleobiologist John Alroy, they confirmed that rate mismatches often coincided with mass extinctions.
Their findings show that mass extinctions occurred when environmental changes exceeded adaptation rates, supporting the global applicability of the rate mismatch hypothesis. This mismatch not only predicts extinction severity but also the fraction of animal life lost during rapid environmental changes, such as the end-Permian extinction where ocean acidification likely led to over 80% marine species extinction.
Although the team’s research focuses on past extinction events, it may also offer insights into modern extinction risks. Rothman warns, “Carbon dioxide levels in the ocean are increasing today at a rate which, when appropriately re-scaled, is similar to rates of carbon-cycle change that are just lower than those associated with major extinction events in the past,” suggesting that current environmental changes could soon surpass adaptation capabilities.
Original Source: news.mit.edu
