Climate Change May Be Making Deer Evolve to Give Birth Earlier in the Year, Scientists Discover

We usually think of evolution as a slow process that takes place over millions of years. However, a team of scientists has now documented how wild red deer on a Scottish island appear to be evolving over the space of decades—possibly in response to climate change—causing them to give birth earlier in the year.

According to a study published in the open-access journal PLOS Biology, these deer—which live on the Isle of Rum just off Scotland's west coast—have experienced genetic changes that have contributed to the animals having children nearly two weeks earlier over the course of the past four decades.

Previous studies by other groups of scientists have demonstrated that the deer on this island have been giving birth earlier, partly as a result of warmer temperatures that have altered their behavior and the functioning of their bodies.

However, the latest study shines a light on the important role of adaptive genetic changes in this process. The researchers say that this work represents some of the first evidence that evolutionary changes are affecting the time of year that wild animals give birth.

"This is one of the few cases where we have documented evolution in action, showing that it may help populations adapt to climate warming," Timothée Bonnet, lead author of the study from the Australian National University, said in a statement.

For their research, Bonnet and colleagues examined field records and genetic data scientists have collected from the deer population living on the island between 1972 and 2016.

"That red deer population has been monitored intensively for various research questions since the 1970s—and even before in less detail"—Bonnet told Newsweek. "That's why researchers have been able to notice changes in birth dates over the years. That's the fundamental motivation for our study: trying to understand that change."

red deer calf, Isle of Rum, Scotland
Red deer calf on the Isle of Rum, Scotland. J Pemberton

The team's analysis revealed that those female red deer—known as hinds—with genetic adaptations that caused them to give birth earlier in the year tended to have more offspring over an individual lifetime. Thus, the genes responsible offer an evolutionary advantage and have become increasingly common in this deer population over the past decades as a result.

"We found that the genetic composition of the population had changed to pull birth dates earlier into spring," Bonnet said. "We found that the genetic change is probably a response to natural selection, but we don't know what causes selection—could be climate change, change in the population density, or any unknown factor that has changed in the last decades."

"It is very difficult to say when climate change causes genetic change, but genetic change happens at a speed similar to direct (non-genetic) responses to climate warming and sufficiently fast to matter in ecological dynamics related to climate change," he said.

Sally Thomas from Scottish Natural Heritage, who was also not involved in the study, said: "These findings are a fascinating example of the impact climate change may be having on wildlife. More and more research is demonstrating climate change is influencing species across the U.K. and the world."

Climate change is affecting life on our planet Earth in a variety of ways and scientists say that for species to survive they must adapt by undergoing genetic shifts or migrating to more suitable habitats, for example.

But recent research published in the journal Proceedings of the National Academy of Sciences suggests that genetic adaptation coupled with dispersal into new ranges could bring species into conflict with one another.

This finding could mean that scientists have been underestimating how global climate change will affect biodiversity and the number of extinctions that will occur.
Some scientists have argued that the Earth is currently experiencing its sixth mass extinction, with species disappearing significantly faster than historical baseline rates.

In fact, a landmark U.N. report recently warned that 1 million species around the world are at risk of disappearing due to human pressures and climate change.

This article was updated to include additional comments from Timothée Bonnet.