Like humans, kangaroos prefer using one hand over the other for everyday tasks like reaching for branches or holding on to snacks. And as it turns out, most roos are lefties! The work, published in Current Biology, is the first study to look at handedness in wild kangaroos and wallabies. Having a preference isn’t as unique to humans as some researchers previously thought, although the evolution of bipedalism among marsupials and primates may have led to the trait.
No one really expected to find “true handedness” in marsupials, since they lack the neural circuit that bridges the left and right brain hemispheres found in other mammals. But previous work did reveal weak signs of handedness in marsupials that walk on all fours, such as sugar gliders and gray short-tailed opossums.
To see if that’s also the case for bipedal marsupials, a team led by Yegor Malashichev of Saint Petersburg State University observed more than 70 animals spanning four species of kangaroos and wallabies in Australia and Tasmania. "What we observed in reality we did not initially expect," Malashichev says in a statement. "But the more we observed, the more it became obvious that there is something really new and interesting in the wild."
Wild kangaroos, they found, naturally preferred using their left paws to perform actions such as grooming their own nose, bending a tree branch, and picking a leaf. This left-handedness was especially apparent in eastern grey kangaroos (Macropus giganteus, pictured above) and red kangaroos (Macropus rufus).
A red-necked wallaby manipulating food with one forelimb. Courtesy of Andrey Giljov and the National Geographic Society
Red-necked wallabies (Macropus rufogriseus, pictured just above), on the other hand, seemed to alternate between their right and left hands, depending on the task. In general, they use their left paws for tasks involving fine manipulation, such as directing stems and leaves to their mouths; they use their right paws for tasks that require more physical strength, like supporting branches. This division of labor in wallaby hand-use might be linked to their ecology and eating habits. While eastern grey and red kangaroos are grazers, the wallaby diet includes more trees and shrubs, and this browsing may require specific motor demands.
And then there’s Goodfellow’s tree-kangaroo (Dendrolagus goodfellowi) who doesn’t seem to show much of a preference. As their name suggests, they spend most of their days in trees, and they’ve adapted a quadrupedal locomotion—similar to the gliders and possums in the previous studies. This supports the idea that quadrupedality hinders the expression of forelimb preferences in populations. Bipedalism may have been a catalyst for the emergence of handedness in humans.