Will climate change make animals darker—or lighter?
A 19th century claim has fueled a 21st century debate about how a warming climate might reshape animals. Beginning in the early 1800s, biologists identified multiple “rules” describing the ecological and evolutionary impacts of temperature. One rule held that animals have bigger appendages (ears, beaks) in hot climates, to help dissipate body heat. Another said that, within any group of animals, the biggest generally reside closer to the poles—think of polar bears towering over midlatitude brown bears—because larger bodies help retain heat.
And Gloger’s rule, named after German biologist Constantin Gloger, declared that animals in warmer regions usually have darker exteriors, whereas those in cooler regions are lighter. Among mammals, darker skin and hair was thought to protect against damaging ultraviolet light, which is more plentiful in Sun-soaked equatorial areas. Among birds, the specific melanin pigments in darker feathers seem to resist bacterial infestation, an advantage in the Petri dish of the tropics.
Back in July, Li Tian of the China University of Geosciences and Michael Benton of the University of Bristol revived interest in these largely forgotten rules when the two paleontologists used them to predict how climate change might remake animal bodies. Among other things, they relied on Gloger’s rule to propose that, as Earth warms, most animals would get darker. Simple enough.
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