Can species evolve fast enough to survive as the planet warms?

For the first time, we have seen a species that was in decline due to extreme weather recover through rapid development. Does this mean that species increasingly affected by high temperatures and other challenging conditions can adapt as the planet warms?

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

But the key issue is time. Until now, the most rapid climate change we know was the Paleocene-Eocene Thermal Maximum, which occurred about 56 million years ago, when temperatures rose 5 °C to 8 °C over a period of about 20,000 years. Temperatures may now rise by more than 4°C towards the end of the century. Can evolution really make a difference in 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 monkey flower (Mimulus cardinalis), which managed to evolve out of the mega-drought that hit California between 2012 and 2015.

Daniel Anstett of Cornell University in upstate New York 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.

Monkey flowers 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 actually died out. But many of those that survived appear to have developed drought tolerance in just three years, with many mutations in parts of the genome linked to climate adaptations – and it was these populations that recovered the fastest from the drought.

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

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

There are many possible examples of evolutionary rescue, including finches in the Galapagos that change in response to drought, Tasmanian devils that evolve in response to a transmissible cancer, pests that develop resistance to pesticides, and killifish that adapt to cope with extreme levels of pollution in American rivers. But biologists have not been able to tick all three boxes in these cases, says Anstett.

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

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

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

In other words, the fact that monkeyflowers were able to evolve to survive an extreme drought does not necessarily mean that they will be able to evolve to cope with a century or more of rapidly rising temperatures and increasingly extreme weather. “Extremes in the future may overshadow the drought we saw,” says Anstett.

Also, as populations decline, they lose genetic diversity—the fuel for evolution. If populations are repeatedly hit hard over a short period of time, their capacity to evolve decreases each time.

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

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