Kangaroos Are All Left-Handed?

It turns out that all kangaroos are left-handed, new research shows.

While some animals have demonstrated a preference for a certain hand (or paw) in the past, it was previously believed that handedness was unique to primates such as humans. Now, researchers report in the journal Current Biology that this is not the case; and that kangaroos are even more true-handed than we are.

"According to a special-assessment scale of handedness adopted for primates, kangaroos pulled down the highest grades," Yegor Malashichev of Saint Petersburg State University in Russia said 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 previously found that some species of walking frogs show handedness, while jumping frogs are less likely to do so. In addition, marsupials that walk on all fours - including gray short-tailed opossums and sugar gliders - have shown hints of handedness. But until now, no one had thought to look at bipedal kangaroo species.

That's because, as marsupials, kangaroos lack the same neural circuit that bridges the left and right hemispheres of the brain.

"What we observed in reality we did not initially expect," Malashichev said. "But the more we observed, the more it became obvious that there is something really new and interesting in the wild."

In the new study, Malashichev and his colleagues observed four species of marsupial in the wild at Tasmania and Australia: the eastern gray and red kangaroos, as well as the red-necked wallaby (Macropus rufogriseus) and the Goodfellow's tree-kangaroo (Dendrolagus goodfellowi).

They found that wild kangaroos favor their left forelimbs when performing certain tasks like feeding and grooming. Eastern gray and red kangaroos, in particular, were shown to be southpaws.

Meanwhile, red-necked wallabies 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.

These findings certainly give researchers cause to look at marsupials in a different light. Kangaroos are well removed from the primate lineage, suggesting that handedness is something that has evolved independently over time. They hope to explore more the marsupial brain and handedness in other upright species in the future to learn more.

"This will give us a better resolution for the evolutionary interpretations," Malashichev concluded.

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