The climate crisis could lead to the human race shrinking as mammals with smaller frames seem better able to cope with rising global temperatures, a leading fossil expert has said.
Professor Steve Brusatte, a paleontologist at the University of Edinburgh, suggested how other mammals have previously responded to periods of climate change could offer insight into the future of humans.
He compared the potential fate of people to that of the first horses, which became smaller in size as temperatures increased about 55 million years ago, a period called the Paleocene Eocene Thermal Maximum.
“There’s a big fossil record through this global warming event, it’s really the most recent big global warming event in the geological record,” he said. “The two plots are strange, how similar they are.”
Writing in The Rise and Reign of the Mammals, Brusatte notes that animals in warmer parts of the world today are often smaller than those in colder regions, an ecological principle known as Bergmann’s rule. “The reasons are not fully understood, but it is probably, in part, because small animals have a higher surface area to volume ratio than plumper animals and can therefore conduct excess heat better,” he writes.
Speaking to the Guardian ahead of the book’s publication, Brusatte said getting smaller was “a common way for mammals to cope with climate change”. He added: “That’s not to say that all mammal species would get smaller, but it does seem to be a common mammalian survival trick when temperatures rise quite quickly. Which begs the question: if temperatures rise very quickly, could humans become dwarfs, could humans become smaller? And I think that’s certainly plausible.
Brusatte argued that other human species shrank when resources were scarce – pointing to the so-called hobbit humans, Homo floresiensis, who once inhabited the island of Flores in Indonesia.
In a recent study, researchers studying human remains over the past million years have also suggested that temperature is a major predictor of variation in body size, while scientists studying red deer have said that warmer winters in northern Europe and Scandinavia could cause a decrease in the body size of these animals.
However, all experts I agree that rising temperatures cause mammals to shrink. Professor Adrian Lister, from the Natural History Museum in London, said the relationship shown by the recent human remains study is weak, while the strong correlations between temperature and body size in mammals can often be due to the availability of food and resources.
Lister is also skeptical that humans will decline as the climate warms. “We’re not really controlled by natural selection,” he said. “If this were to happen, tall people would have to die before they could reproduce because of global warming. This does not happen in today’s world. We wear clothes, we have heating, we have air conditioning if it’s too hot.
However, Brusatte says that while humans are an amazing species, other mammals might be better off without us. “You could say, are other mammals better off if humans weren’t there? And you know, frankly, probably, yes,” he said. “I think if you were a rhino, an elephant, a lion, a platypus, a koala, you probably wish humans would go extinct. But hopefully that won’t happen.”