Climate crisis: do people have to shrink?

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Smaller is better: those who grow taller are less able to regulate body heat

Photo: Getty Images/iStockphoto

When temperatures soar, “could humans shrink?” Paleontologist and evolutionary biologist Steve Brusatte answers his question to the Guardian himself: “I think that's definitely plausible.”

The University of Edinburgh researcher has published a book called The Rise and Reign of the Mammals about the rise of mammals.

In it he refers to Bergmann's rule, according to which warm-blooded animals in cold regions grow larger than their relatives living in warmer climates.

The reason is believed to be that smaller animals have a larger skin surface in relation to their body volume and are therefore better able to dissipate excess heat to the environment.

Getting smaller, according to Brusatte, is a “common way that mammals deal with climate change”.

The warming that is taking place today is amazingly similar to the Paleocene/Eocene temperature maximum of almost 56 million years ago, the “youngest major global warming event for which we have geological data”.

At that time, the ancestors of horses had shrunk by 30 percent within around 130,000 years before they grew larger again in the subsequent cold phase.

"It doesn't mean that every species of mammal is getting smaller, but it does seem to be a common survival ploy when temperatures soar really fast," Brusatte told the British newspaper.

There are also examples of this in the history of human development, such as the human species Homo floresiensis, also known as “hobbits”, on the Indonesian island of Flores.

In the tropical forest, the Floresians, descended from Homo erectus, which can be up to 1.80 meters tall, apparently shrank to only about one meter in a short time.

According to a study published in Nature Communications in 2021, temperature appears to be a major factor influencing human height as measured in bone finds.

Adrian Lister from the London Natural History Museum expressed skepticism to the Guardian.

The connection between temperature and body size is rather weak in humans, but in animals it can often be explained by the availability of food and other resources.

But above all: "We are not really subject to natural selection," says Lister.

For evolution to strike like Brusatte's scenario, tall people would have to die in the warmer world before they could reproduce.

"That doesn't happen in today's world," Lister said.

"We wear clothes, we have heaters, we have air conditioning if it gets too hot."

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