Research on wild kangaroos in Australia is challenging the notion that having a strong hand preference is a trait that developed primarily in people and other primates.
Scientists said on Thursday that these Australian marsupials displayed a natural preference for using their left hand for feeding, self-grooming and other activities. So while most people are right-handed, most kangaroos are lefties.
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Beyond providing new insight into kangaroo behavior, the research sheds light on a unique aspect of mammalian evolution, the researchers said.
"We found a pronounced degree of 'handedness,' comparable to that in our species," said biologist Yegor Malashichev of Saint Petersburg State University in Russia. "In bipedal kangaroos, in all actions studied, there was a significant left-hand preference in the vast majority of individuals."
The researchers said they did not expect to find hand preference in kangaroos or other marsupials — the pouched mammals — because of brain differences from the more common placental mammals, including primates, the researchers said.
"Any study that proves true 'handedness' in another bipedal (two-footed) species contributes to the study of brain symmetry and mammalian evolution," said wildlife ecologist Janeane Ingram of the University of Tasmania in Australia, another of the researchers. "Even in the scientific community, true 'handedness' was assumed to have evolved primarily in humans and primates."
Kangaroos are herbivores with strong legs, large feet and a large muscular tail. They use hopping as their primary means of locomotion, and their upright stance allows them to use their hands freely.
The researchers observed two bipedal species of kangaroos and one bipedal species of wallaby, a smaller member of the kangaroo family, in continental Australia and the island of Tasmania off the country's southern coast.
They found that two large, bipedal species, the eastern gray kangaroo and the red kangaroo, exhibited left-handedness in all tasks, including supporting the body with one forelimb in a tripedal stance.
Red-necked wallabies, when eating from tree branches, used the left hand, as two other kangaroo species did, to manipulate the leaves while holding the branch with the right hand.
The researchers found less evidence for hand preference in Australia's tree kangaroos.
The research, backed by the National Geographic Society, was published in the journal Current Biology.