All kangaroos are left-handed, according to new research.
Previously it was thought that "true"-handedness, meaning predictably using one hand over the other, was a feature unique to primates. The new research, published in the journal Current Biology, not only negates that but also goes one step further: kangaroos are even more true-handed than we are.
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"According to a special-assessment scale of handedness adopted for primates, kangaroos pulled down the highest grades," said project leader Yegor Malashichev in a press release. "We observed a remarkable consistency in responses across bipedal species in that they all prefer to use the left, not the right, hand."
Malashichev, a researcher from Saint Petersburg State University in Russia, and his team observed that wild kangaroos show a natural preference for their left hands when performing particular actions, such as grooming their noses, picking leaves, or bending tree branches. Left-handedness was particularly apparent in eastern grey and red kangaroos.
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The kangaroos that they studied were at various locations in the wild at Tasmania and Australia. The term "hand" really does apply here, because kangaroos have five-fingered hands that somewhat resemble human hands, save for the kangaroos' long claws in place of fingernails.
Not all marsupials were found to exhibit such handedness. The researchers determined that red-necked wallabies, for example, prefer their left hand for some tasks and their right for others. Generally speaking, these wallabies use their left forelimb for tasks that involve fine manipulation and the right for tasks that require more physical strength. The researchers also found less evidence for handedness in species that spend their days in the trees.
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The discovery about kangaroos was unexpected because, unlike other mammals, kangaroos lack the same neural circuitry that bridges the left and right hemispheres of the brain. Now the researchers are very curious about marsupial brains, which differ from those of other mammals in additional respects too.
Such studies could yield important insight into neuropsychiatric conditions, including schizophrenia and autism, the researchers said, noting links between those disorders and handedness.