Kangaroos and other macropod marsupials display left-hand preference at the population level for everyday tasks in the wild, says a team of scientists including Janeane Ingram from the University of Tasmania, Australia. This result challenges the notion that in mammals the emergence of ‘true’ handedness is a unique feature of primate evolution.
A red-necked wallaby (Macropus rufogriseus) manipulating food with one hand. Image credit: Andrey Giljov / National Geographic Society.
One reason ‘true’ handedness wasn’t expected in kangaroos is because, unlike other mammals, they lack the same neural circuit that bridges the left and right hemispheres of the brain. Studies of kangaroos living in captivity hadn’t yielded conclusive evidence either.
In a new study, published online today in the journal Current Biology, Ms Ingram and her colleagues watched these animals in Tasmania and continental Australia.
They found that wild kangaroos show a natural preference for their left hands when performing particular actions – grooming the nose, picking a leaf, or bending a tree branch.
Left-handedness was particularly apparent in the eastern gray kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus).
Red-necked (Bennett’s) wallabies (Macropus rufogriseus) prefer their left hand for some tasks and their right for others: they use their left hand for tasks that involve fine manipulation and the right for tasks that require more physical strength.
The scientists found less evidence for handedness in species that spend their days in the trees.
“The findings should encourage more careful study of the marsupial brain, which differs from those of other mammals in many respects,” they said.
“Such studies might even yield important insight into neuropsychiatric conditions, including schizophrenia and autism.”
The team plans to continue exploring handedness in other species that stand upright regularly or from time to time.
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Andrey Giljov et al. Parallel Emergence of True Handedness in the Evolution of Marsupials and Placentals. Current Biology, published online June 18, 2015; doi: 10.1016/j.cub.2015.05.043
