Kangaroos have a preference for which hand they use, just like humans do, but with one startling difference: the majority of the Down Under hoppers are left-handed.
Kangaroos observed in the wild in Tasmania and on continental Australia were found to have a preference for using their left forelimbs for most everyday tasks, such as feeding and grooming, researchers say.
The finding goes against the long-held assumption that "true" handedness — a consistent preference for using one hand across a wide range of behaviors at the population level — was unique to humans.
Writing in the journal Current Biology, researchers report that not only have kangaroos put that assumption to rest, but also that the bipedal marsupials are even more "true"-handed than we are.
"According to a special-assessment scale of handedness adopted for primates, kangaroos pulled down the highest grades," study leader Yegor Malashichev from Saint Petersburg State University in Russia says. "We observed a remarkable consistency in responses across bipedal [marsupial] species in that they all prefer to use the left, not the right, hand."
The researchers say they hadn't expected to find handedness in kangaroos, primarily because, unlike most mammals — including humans — they lack a common neural circuit that connects the right and left hemispheres of the brain.
However, in watching eastern gray and red kangaroos, they noted the animals' preference for using the left forelimb for tasks such as grooming the nose, plucking a leaf from a tree or bending a branch to get to the leaves.
"What we observed in reality we did not initially expect," Malashichev says. "But the more we observed, the more it became obvious that there is something really new and interesting in the wild."
Kangaroos' forelimbs end in five-fingered appendages that somewhat resemble human hands, although, instead of fingernails, they end in long claws.
Because human handedness has shown associations with neuropsychiatric conditions, including schizophrenia and autism, the findings suggest further studies could yield important insights into such links, the researchers say.
Further detailed study of the marsupial brain — different from other mammals in many particulars — could be useful in that regard, they say.
Malashichev says he and his colleagues have plans to explore the phenomenon of handedness among other bipedal species that spend much of their time standing upright.
"This will give us a better resolution for the evolutionary interpretations," he says.
