Kangaroos are left handed

一些澳大利亚的有袋动物,包括袋鼠d wallabies, show signs of left handedness, a new study has shown.

Hand preference - the repeated preferred use in a population ofone appendage over the other when performing certain tasks - is widely hailed to be a trait unique to primates. Amongst humans, 90% of us are right handed, although scientists aren't entirely sure why.

Some have speculated that this reflects the dominance of the left sides of our brains, which is also where language is chiefly processed.

Other animals, including horses, dogs and dolphins do show a preferred side, but unlike humans, there are usually equal numbers of right and left "handers" in the population, suggesting that the side preference in these species is just down to chance.

It will therefore come as a surprise for some to learn that a new study on a range of Australia marsupial species has found that some of them are strongly left handed.

Andrey Giljov, from Russia's Saint Petersburg State University, and his colleagues studied the natural movements seven different marsupial species, including red and grey kangaroos, wallabies and opossums.

Quadrupedal marsupials, like the sugar glider and Goodfellow's tree kangaroos, show no obvious paw preferences. But marsupial species that tend of operate on two legs, on the other hand, such as the wallabies, kangaroos and even the more distantly-related bettongs, showed strong preferences for using their left paws when foraging and feeding.

Not needing to hang onto branches in trees, or to remain stable on four limbs - which might require one or the other hand, or paw at any moment in time - appears to have allowed these animals to evolve a hand preference.

"The emergence of different roles for the right and left forelimbs may be associated with the need to perform distinct manual tasks," say the team in their paper this week in Current Biology. "We hypothesise that the specialisations of forelimb functions have been shaped under the pressure of ecological factors."

The brain basis of the animals' behaviour isn't understood and, unlike humans, the marsupial brain isn't known to have a dominant hemisphere. This means that the neurological mechanisms that determine hand preference could be quite different between marsupial and mammalian species.

"The neurobiology of manual lateralisation in marsupials is an important subject for future research," the researchers acknowledge.