Some animals and plants are rapidly adapting to our warming, polluted world. How alarming that is depends on your perspective.
Charles Darwin thought
of evolution as an incremental process, like the patient creep of glaciers or the march of continental plates. “We see nothing of these slow changes in progress until the hand of time has marked the long lapse of ages,” he wrote in
On the Origin of Species,
his famous 1859 treatise on natural selection.
But by the 1970s, scientists were finding evidence that Darwin might be wrong—at least about the timescale. Peppered moths living in industrial areas of Britain were getting darker, better for blending in against the soot-blackened buildings and avoiding predation from the air. House sparrows—introduced to North America from Europe—were changing size and color according to the climate of their new homes. Tufted hairgrass growing around electricity pylons was developing a tolerance for zinc (which is used as a coating for pylons, and can be toxic to plants).
In the late 1990s, biologist Andrew Hendry noticed similarly quick changes in phenotype while studying salmon. (Phenotype refers to the trait that actually exists in the animal, even if it’s not reflected by a change in its underlying genetic code.) “We had this impression that well, actually, maybe this rapid evolution thing is not so exceptional,” says Hendry, now a professor at McGill University in Montreal. “Maybe it’s actually occurring all the time, and people just haven’t emphasized it.”
With a colleague, Michael Kinnison (now at the University of Maine), Hendry pulled together a database of examples of rapid evolution and wrote a 1999
that kickstarted interest in the field. Now, Hendry and colleagues have updated and expanded the original data set with more than 5,000 additional examples: everything from the cranial depth of the common chaffinch to the lifespan of the Trinidadian guppy. Scientists are using this data to answer questions about how fast and far the natural world is changing, and how much of the change is due to humans.
In an initial
published in November 2021 using the new data set (which is called
, for Phenotypic Rates of Change Evolutionary and Ecological Database), Hendry and colleagues reexamined five key questions raised by previous work. They confirmed, for instance, that on average, all over the world, animal species seem to be getting smaller. This runs contrary to a theory of evolution called Cope’s rule, which posits that species should increase in size over time. “It’s better to be larger,” says Kiyoko Gotanda, a coauthor on the paper who is now at Brock University in Ontario. “You’ll get more mates, you have a better survival rate.” But when they analyzed the new data, the results confirmed a finding from a previous paper by Gotanda. “There seems to be an overall decline in body size due to things like climate change, and other types of human influences,” she says.
Hunting and harvesting are the biggest drivers of this trend: If humans pluck the fattest fish from the ocean each time they cast their nets, it follows that
only the smaller ones will survive
to pass on their genes. But climate could also play a role because of a basic rule of biology: Larger creatures have a bigger surface area to volume ratio, and therefore find it easier to retain heat. “The theory is that you don’t need to maintain that larger body size as the temperatures are warming, and so you can be smaller,” Gotanda says.
This might seem like a minor concern, in the wake of
and mass extinction, but it could have serious knock-on effects. Take salmon for instance: Smaller fish mean less money for the communities who rely on catching them. It means less food for the wolves and bears that feed on them. It means they produce proportionally fewer eggs, which play an important role in adding nutrients to the rivers when salmon return there to spawn. “Reduction in salmon body size is directly affecting nature’s contributions to people, and that results in less protein, less eggs, less salmon returning, and has huge effects on the ecosystem at multiple levels,” says Sarah Sanderson, the paper’s lead author and a biology PhD candidate at McGill.
Trait changes can have similar effects. A 2021
in Mozambique’s Gorongosa National Park found that the proportion of female elephants being born without tusks has shot up to more than 50 percent, as extreme levels of poaching during a 15-year civil war turned survival of the fittest on its head. Elephants without tusks were far more likely to pass on their genes to the next generation. Tuskless elephants won’t shape ecosystems in the same way as their toothier brethren: They won’t tear up the soil as much when digging for tubers, for instance. And analyzing DNA in their feces revealed that tuskless elephants eat different plants.
To compare changes across species over time, the researchers used metrics called darwins and haldanes (after the British scientist JBS Haldane). These are statistical measures that offer a way to compare the vastly different types of information in the database—from the height of birch trees growing near smelting operations in Russia to how the acidification of Swedish lakes is affecting frog survival rates.
The new analysis found that rates of phenotypic change were higher in populations affected by human activity than those that were not. But the researchers were surprised to find little evidence isolating climate change as the cause of phenotypic change. Pollution seemed to be a much bigger driver, responsible for changes like the ones observed in the Russian birches and the Swedish lakes. “We think that’s because it’s hard to say what’s [caused by] climate change versus something else,” says Hendry. “Climate change is happening everywhere.”
The effects of climate change will not be felt evenly all over the world: In the Arctic, it might mean polar bears developing new hunting behaviors that don’t rely on ice; in the oceans, it might mean that strains of coral already adapted to living in stressful environments
become the dominant species
, supplanting the ones we now know. “A lot of them are evolving really fast in response to these changes,” says Sanderson. “But what you don’t see, and what we can’t really quantify [with this work] is all these populations that aren’t adapting, and that are going extinct.”
The Proceed database is available
for academics hoping to answer new questions about rapid evolution. For now, it has confirmed that human actions are changing animal and plant species in ways that they may never recover from—the natural world forever marked by pollution, and that uniquely human desire to hunt and harvest long past the point of individual satiety.
That may seem grim, but you can interpret these results in a reassuring way too. If we overfish to the point where species start to shrink, well maybe that’s just a sign that humans are not immune to the feedback loops that govern every other living thing. The animals we know will change or disappear, and new ones will evolve to take their place—life will endure, even if life as we know it doesn’t. “Because of studies like these I don’t have any fear about life on Earth under climate change,” says Thomas Cameron, a senior lecturer in animal ecology at the University of Essex, who was not involved in the research. “The natural world will still exist, but it may not be the same world and some species will go extinct. But others will change and evolve.”
This work, Cameron says, reinforces the idea that evolution is happening all the time—small changes adding up to the big ones over the long lapse in ages. Despite everything we’ve thrown at them, this research shows that some animals and plants will be able to adapt quickly enough to outpace the warming planet—they’ve been doing it for millions of years.
That’s a reassuring thought, but also a scary one, because others won’t survive. For them, the pressures of pollution and climate change will overwhelm their ability to respond. It’s up to us how much change we can accept. The world that human pressures create might look very different from the one that our own species has adapted to live in. “This work tells us that populations have and always will change in response to their environment,” Cameron says. “Society expects to open the curtains in the morning and see a particular form of landscape and biodiversity. That’s not what nature is about. Nature is about change.”
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AUTHOR: AMIT KATWALA
BIO: SENIOR WRITER AT WIRED WITH A FOCUS ON LONGFORM FEATURES, SCIENCE, & CULTURE. HE GRADUATED FROM THE UNIVERSITY OF OXFORD WITH A DEGREE IN EXPERIMENTAL PSYCHOLOGY, & IS THE AUTHOR OF TWO BOOKS: THE ATHLETIC BRAIN, ABOUT THE RISE OF NEUROSCIENCE IN SPORT, & A WIRED GUIDE TO QUANTUM COMPUTING. HE IS BASED IN LONDON.