Kangaroos Are Lefties, Science Says

In a fight, would a kangaroo jab right and cross left? These two juvenile kangaroos dance around each other as they fight in Namadgi National Park near Australia's capital city, Canberra. Tim Wimborne/Files/Reuters

It was once thought that handedness was unique to humans, but studies in the early 20th century began to show that the trait also existed in primates.

But it appears that it is not exclusive to primates either. Scientists have now found that kangaroos and other marsupials—mammals whose underdeveloped young often dwell in pouches in their bodies—generally favor their left limbs over their right.

Yegor Malashichev, a researcher at St. Petersburg State University, and colleagues spent hours and hours observing red and eastern gray kangaroos, wallabies and other animals in the wild. They found that kangaroos and wallabies had a strong preference for using their left forelimbs for such tasks as feeding, grooming and the like. Red-necked wallabies preferred to use their left limbs for fine motor tasks, like picking up things, but opted for their right for feats that required strength.

The finding—published Thursday in the journal Current Biology—serves as a clue to how handedness evolved and, says Malashichev, "may tell us about some fundamental differences in functioning of [the animals'] brains and distribution of functions between the hemispheres." The reason why humans and other animals favor one limb over the other is a result of an asymmetric development of the brain, he explains.

But why are kangaroos lefties? Malashichev can't say exactly why they favor one limb over the other. Handedness is all over nature and seems pretty random. His research also shows that orangutans "seem to be more lefties. Even amphibians have handedness: Gray toads "wipe the snout preferentially with [the] right forelimb, others—green toads—with the left one." Bees also appear to favor one antenna over the other, as shown in studies by Giorgio Vallortigara, a professor of neuroscience at the University of Trento in Italy.