In 1847, zoologist Christian Bergmann proposed that mammals and birds that live in cold climates tend to be larger than those that live in warm climates. This is because larger animals have a smaller ratio of surface area to volume, meaning they retain heat better, he said.
That's why the woolly mammoth grew so much, and natural selection favored larger, cold-resistant animals. But as the planet warmed and emerged from the Ice Age, the mammoths had trouble adapting and went extinct, with little help from human hunters.
Scientists believe that as the planet warms, there is natural selection for animals to become smaller. This is most clearly seen in animals that live in areas where temperatures are very high, such as polar bears in the Arctic.
“Habitat destruction due to climate or environmental change can exacerbate these conditions, which can lead to a rapid decline in the size of the animals and, ultimately, extinction. Due to the warming of the planet, polar bears face melting ice and habitat loss, moving forward a little further,” he said. “From the simulation study we did, I think it could decline faster over time,” Roy told DW.
