How the climate has shaped our bodies
Humans have fluctuated in size significantly over the past million years because of changes in the climate, a new study suggests. Researchers took measurements from more than 300 fossils from the Homo genus, the family to which modern-day humans—Homo sapiens—belong. They then calculated the regional climate experienced by each of these hominins when they were alive. Climate, and in particular temperature, was found to be the main driver of changes in body size: In cold, harsh climates body size was larger, while warmer climates were linked to smaller bodies. “Larger bodies can buffer individuals from cold temperatures. The larger you are, the smaller your surface compared to your volume, so you conserve heat more efficiently,” co-author Andrea Manica, from the University of Cambridge, tells CNN .com. This relationship between climate and body mass can be seen in the animal kingdom: Polar bears in the Arctic, for example, weigh more than brown bears in warmer climes. And it applies broadly to modern humans: the average Dutch man is 6 feet tall, whereas the average Indian man is 5-foot-5. The researchers found no association between temperature and brain size. Because humans evolve over many generations, the researchers say, it will take thousands of years for our bodies to change in response to global warming on its current course. Even then, the changes will be small, about 2 pounds per 3.6 degrees of warming, Manica says. “We’re not going to shrink tomorrow.”