Handedness (the preference for using one hand over the other for nearly all tasks) likely emerged in humans soon after we began to walk upright. And for years scientists have thought this trait belongs almost exclusively to bipedal primates, given it's never before been observed in quadruped creatures. Now they've found that red and eastern gray kangaroos appear to exhibit even truer handedness than humans—and they prefer the left to the right, researchers from Russia report this week in the journal Current Biology. As the study observes, "This result challenges the notion that in mammals the emergence of strong 'true' handedness is a unique feature of primate evolution." The lead researcher speculates that handedness also emerged in these marsupials when they began to walk on two instead of four legs.
Not all marsupials exhibit a preference for one hand over the other, reports Discovery. For example, red-necked wallabies tend to use their left hands for some tasks and their right for others. The team also observed that tree kangaroos, which use all four limbs to climb, also display no preference for one hand over the other, reports National Geographic. Red and gray kangaroos, however, were the exception, preferring their left hands for tasks such as grooming and eating regardless of whether they were standing on two or four legs. The findings especially surprised the scientists because kangaroo brains are not connected across hemispheres the way other mammalian brains are, so studying their brains more closely could provide some clues about neuropsychiatric conditions such as autism. (Kangaroos also use their tails in quite a distinctive way.)