Last year in Australia, I visited Featherdale Wildlife Park where, in a couple of areas, kangaroos and wallabies hop amongst the tourists. For a dollar, you can buy an ice cream cone full of grass for the marsupials to eat. But if you’re not careful, an animal will quickly grab the cone out of your hand and feed itself.
Now I’m wishing that I had paid more attention to that grabbing motion.
Kangaroos are lefties, scientists report June 18 in Current Biology. And the preference for one hand over the other may be linked to the ability to walk on two legs.
Humans show a definite preference for one hand over the other, usually the right. This handedness had been considered a distinctly human trait. But scientists have found more and more evidence that other species have such preferences as well. Female domestic cats, for instance, tend to use their right paws and males their left.
Andrey Giljov of Saint Petersburg State University in Russia and colleagues were curious about the evolution of handedness and looked to marsupials, since these animals are an early offshoot of the mammal lineage. They observed four species in the wild — red kangaroos, eastern gray kangaroos, red-necked wallabies and Goodfellow’s tree kangaroos — performing tasks such as grooming and feeding.
The red and eastern gray kangaroos showed a preference for using their left forelimbs for all tasks. The red-necked wallabies used their left forelimb for tasks that required fine manipulation and their right for tasks that needed strength. The tree kangaroos, though, had no preference for either limb in any task.
The big difference between the three species that exhibited handedness and the one that didn’t is whether the animals walked on two legs or four. The kangaroos and wallaby are bipedal; the tree kangaroos are quadrupedal. Other marsupial species also fit this pattern. Quadrupedal sugar gliders and gray short-tailed opossums are not handed, while the bipedal brush-tailed bettong displays handedness in most tasks.
Previous studies have suggested that walking on four legs inhibits the development of handedness, the researchers note, and these results appear to bolster that hypothesis. And the differences between the two kangaroo species and the wallaby may be explained by ecology. The kangaroos are grazers. The wallaby feeds on trees and shrubs. That browsing behavior may require a level of skill for fine manipulation that the kangaroos just don’t ever need to develop.
Studies of the marsupial brain may provide more insight into handedness, the researchers say. Unlike humans and other mammals on our branch of the family tree, marsupials don’t have a neural circuit that links the right and left hemispheres of the brain. Because of that, scientists didn’t expect to find evidence of handedness in any marsupial, so that kangaroos and wallabies may be lefties is a surprising find.