Left-Pawed Kangaroos Challenge What We Thought We Knew About Animal Evolution

A kangaroo reaches up with its left paw to groom its face, then uses that same paw to pluck leaves from a branch. It does this not once, but almost every time. An international team of researchers watching these animals in the Australian bush and in zoos across the world has documented something that upends a long-held assumption about evolution: handedness is not unique to humans and apes.

For decades, scientists believed that the preference for one hand or paw over the other was a trait that emerged only in primates and humans—a marker of our evolutionary sophistication, a sign of how our brains had reorganized themselves over millions of years. But red kangaroos and eastern grey kangaroos, two of Australia's most iconic marsupials, show an almost absolute preference for their left paw when feeding and grooming, regardless of whether they are standing upright or moving on all fours. This discovery, led by zoologist Yegor Malashichev of Saint Petersburg State University and funded by National Geographic's Committee for Research and Exploration, forces a reconsideration of how and why this trait evolved across mammalian species.

Malashichev's team spent years observing kangaroos in Tasmania and on the Australian mainland, as well as in zoos in Sydney and Europe. They studied three species in the wild—red-necked wallabies, red kangaroos, and eastern grey kangaroos—and added observations of tree-dwelling Goodfellow's kangaroos from Papua New Guinea. The pattern that emerged was striking. Red-necked wallabies showed left-paw preference only when standing on two legs. But red and eastern grey kangaroos used their left paw almost exclusively for feeding and grooming, whether upright or on all fours. The tree-dwelling Goodfellow's kangaroos, which rely on all four limbs to climb, showed no preference at all. This last detail proved crucial: it suggested that upright posture itself might be the key to understanding why handedness develops.

Malashichev first noticed this pattern in 2011 when observing red-necked wallabies, findings he published in the journal Animal Behaviour. The current study, which began in 2012, expanded that initial observation into a broader investigation. What he found challenges the notion that humans are uniquely wired for handedness. "It seems we are no longer so unique," Malashichev told National Geographic, a statement that carries weight given what we thought we knew about our place in nature.

The neurobiological explanation runs deeper than simple behavior. Malashichev argues that handedness in both humans and kangaroos stems from ancient differences in how the brain's two hemispheres function. In most animals, the left hemisphere controls routine tasks through the right side of the body, while the right hemisphere handles emergency responses—fleeing from predators—through the left side. As species evolved upright posture, these differences became more pronounced, allowing one limb to specialize in everyday tasks while the other remained available for quick defensive action. In humans, about 90 percent are right-handed. Kangaroos went the opposite direction, with red and eastern grey kangaroos showing overwhelming left-paw preference.

Paul MacNeilage, a biologist at the University of Texas at Austin who was not part of the study, expressed surprise at the magnitude of the finding. "It's certainly important work, and I was quite struck by how many of these animals were left-handed, given how small their front paws are," he said. MacNeilage offered another hypothesis: the tree-dwelling ancestors of modern kangaroos may have moved primarily using their right side, leaving the left hand free for grooming and feeding—a behavioral pattern that persisted even as their descendants evolved into bipedal hoppers.

Yet the study has limits. MacNeilage noted that the research focused only on marsupials, leaving open the question of whether handedness appears in other animal groups. The absence of preference in tree-dwelling Goodfellow's kangaroos strengthens the case that upright posture drives the development of handedness, but more research across different species and contexts will be needed to confirm this relationship. What remains clear is that the assumption of human uniqueness in this trait has been challenged by animals that hop across the Australian landscape, using one paw with remarkable consistency to feed themselves and keep themselves clean.