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It may seem like a strange title, but this post, which partly continues our celebration of orangutans (see how you can help the endangered species by avoiding palm oil), comes from this week’s Science Friday segment on whether other animals display a preference for left or right in their daily lives, the way humans do. A couple of our contributors here are lefties, making up a small percentage of the total, while 66% of orangutans are left-handed! Nicole Wetsman writes:

The human tendency to be right-handed is obvious—especially if you’re a lefty, and have to deal with right-handed desks and scissors, not to mention spiral notebooks.

But humans aren’t the only members of the animal kingdom that show handedness, or the preference for one hand over the other. Other primates exhibit right-handed or left-handed proclivities, as do animals that don’t technically have hands. For instance, research has shown that some mice are righties while others are southpaws, and that some tree frogs preferentially jump away from predators in one direction over another.

Handedness is related to brain asymmetry—that is, differences in function and anatomy between brain hemispheres. Put simply, the left side controls your right hand and vice versa, and your hand preference is predictive of some of the activity that goes on in each half of the brain.

Brain asymmetry was once considered unique to humans, but now we know that it’s common in vertebrates. “You see asymmetry going all the way down to fish,” says Claudio Cantalupo, who studies handedness and brain asymmetry in humans and nonhuman primates at Clemson University.

Researchers have known for decades that other animals demonstrate handedness. But only recently have they started to learn that, like Homo sapiens, other species can be characteristically handed—meaning that “a statistically significant majority of the individuals in a population prefer one hand to the other,” says Bill Hopkins, who studies lateralization and handedness in primates at Georgia State University.

Hopkins offers some examples from his own research: In chimpanzee populations, about 65-70 percent are right-handed. Gorillas are about 75 percent righty. On the other hand (ahem), about 66 percent of orangutans are lefties.

Now that we have examples of non-human handedness, the next question is, why do animals take sides? In other words, as Hopkins puts it, “what’s the underlying evolutionary mechanism that’s selective for this?” Researchers are still theorizing.

“We’re in no man’s land a little bit,” Hopkins admits.

Read the rest of the article here.