Can species evolve fast enough to survive as the planet heats up?

For the first time, we have seen a species that was in decline due to extreme weather recover through rapid evolution. Does this mean species that are increasingly being hit by soaring temperatures and other challenging conditions can adapt as the planet gets warmer?

It is clear that evolution has saved countless species from climate change in the past. Over the past half a billion years, Earth’s climate has varied from much hotter than it is now – with crocodiles in the Arctic – to much colder. Plants and animals have had to adapt to survive and migrate with shifting climes.

But the key issue is time. Until now, the fastest climate change we know of was the Paleocene-Eocene thermal maximum, which occurred around 56 million years ago, when temperatures rose 5°C to 8°C over a period of roughly 20,000 years. Now temperatures could rise by more than 4°C by the end of the century. Can evolution really make a difference over such a short time?

The answer to that is definitely yes, at least for organisms with short generations. The latest evidence comes from a wild plant called the scarlet monkeyflower (Mimulus cardinalis), which managed to evolve its way out of the megadrought that affected California between 2012 and 2015.

Daniel Anstett at Cornell University in New York state and his colleagues began studying monkeyflowers in 2010, assessing how well the plants were doing at a number of sites across their range each year and taking samples for DNA sequencing.

Monkeyflowers are water-loving plants that live along streams, says Anstett, so they were hit hard by the drought. “If you were to put one in a pot and not water it for a few days, it would just die,” he says.

Three local populations did indeed die out. But many of those that survived appear to have evolved drought tolerance in just three years, with many mutations in parts of their genome linked to climate adaptations – and it was these populations that recovered fastest after the drought.

This is what biologists call evolutionary rescue – a species surviving a threat by rapid evolution. It has been demonstrated in several labs, but Anstett says this is the first time it has been shown to have happened in the wild.

“It’s very hard to show because you need three things,” he says: showing that a population is declining due to a threat, that it has adapted genetically in response and that those genetic changes enabled it to recover.

There are lots of possible examples of evolutionary rescue, including finches in the Galapagos changing in response to drought, Tasmanian devils evolving in response to a transmissible cancer, pests evolving resistance to pesticides and killifish adapting to cope with extreme levels of pollution in US rivers. But biologists haven’t been able to tick all three boxes in these cases, says Anstett.

“That third link, to be able to show that the recovery is explained by rapid evolution, that has never been done before at the scale of an entire range of the species,” he says.

Andrew Storfer at Washington State University, who studies Tasmanian devils, acknowledges this. “To be clear, we’ve demonstrated rapid evolution in Tasmanian devils,” says Storfer. “But with the evidence in hand, we cannot link it to demographic recovery.”

All this said, a three-year drought is weather, not climate. “Demonstrating adaptation to climate change would take a while,” says Storfer.

In other words, the fact that monkeyflowers were able to evolve to survive one extreme drought doesn’t necessarily mean they will be able to evolve to cope with a century or more of rapidly rising temperatures and ever more extreme weather. “Extremes in the future might dwarf the drought that we saw,” says Anstett.

What’s more, when populations decline, they lose genetic diversity – the fuel for evolution. If populations are repeatedly hit hard over a short period, their capacity to evolve gets smaller each time.

So, as global warming continues, the threats will grow ever greater, but species’ capacity to evolve will get smaller. And long-lived species with long generation times have very little capacity for rapid evolution to begin with.

Nevertheless, Anstett sees his findings as good news. “A lot of these current predictions about species decline don’t take evolution into account,” he says. “This is a story of hope.”