A new study has challenged the belief that only humans and primates are left- or right-handed. Researchers have discovered that kangaroos are primarily left-handed, using their left hands to take care of basic tasks like grooming and feeding.
In a joint study conducted by the University of Tasmania and the University of New South Wales, and with the help of scientists from Saint Petersburg State University who conducted the on-the-ground research, the study authors discovered that kangaroos favored their left hand 95 percent of the time.
The study followed wild red-necked wallabies and eastern grey kangaroos at Maria Island National Park and Mount William National Park, both located in Tasmania, as well as red kangaroos at the Fowlers Gap in New South Wales.
"According to a special-assessment scale of handedness adopted for primates, kangaroos pulled down the highest grades," explained project leader Yegor Malashichev. "We observed a remarkable consistency in responses across bipedal species in that they all prefer to use the left, not the right, hand."
"This result challenges the notion that in mammals the emergence of strong 'true' handedness is a unique feature of primate evolution," write the study authors in their paper.
Like primates and humans, kangaroos, a marsupial species, walk on two legs, using their arms and hands to take care of tasks like grooming, picking leaves and grasping tree branches. Kangaroos do not, however, have opposable thumbs, but they do have long claws, differentiating themselves from the hands of primates.
The marsupials did appear to use each hand for a different purpose, the left hand primarily used for tasks that required fine motor skills, and the right, for tasks that required more strength.
"But at both national parks we saw red-necked wallabies always used their right paw for strength work, like pulling a branch down, but always brought the leaves to their mouth using their left paw," said wildlife ecologist Janeane Ingram.
That these kangaroos do walk on two legs seemed to be a major contributing factor to their left handedness. The researchers did not see the same preference for one hand in quadrupeds, finding that the marsupials who use their front legs primarily for tasks other than walking displayed stronger manual lateralization.
According to the BBC, not everyone found this area of research to be as interesting as the scientists who conducted the study. "Unfortunately, even my own colleagues think that studying left-handed macropods is not a serious issue, but any study that proves true handedness in another bipedal species contributes to the study of brain symmetry and mammalian evolution," Ingram told the news agency.
These findings are thought to prompt further study into the brains of marsupials. Because the brain of a kangaroo doesn't have the same neural connections that join the left and right hemispheres of the brain, researchers believe that a kangaroo's left handedness could provide more information on human neuropsychiatric conditions such as schizophrenia and autism. "This will give us a better resolution for the evolutionary interpretations," said Malashichev.