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Like most people on the planet, I'm right-handed, so I never had to worry about getting the side of my hand covered in pencil lead or tracking down that special pair of left-handed scissors. But "handedness" - or a preference to use one hand over the other to complete most tasks - isn't an exclusively human trait. Many other animals have a preference, too. And sometimes handedness isn't even about limbs at all. So here are five examples of handedness across the animal kingdom, from dogs to whales to - yes, the octopuses - that seem to have a favorite arm.

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Given that only about 10% of people living today are lefties, it's safe to say that humanity expresses a species-wide preference for right-handedness. But in other animals, we might only observe handedness at an individual level. So even if my dog, Dewey, is a lefty, it doesn't tell us much about dogs overall. Luckily, there have been multiple adorable studies investigating whether or not our furry companions have a paw preference. One study of 32 dogs even used four different tasks to test for it:

In one task, the researchers noted which paw the dog would use to hold a tasty treat still so they could lick at it; in another, they observed which paw they would use to remove a piece of sticky tape from their boopable snoots; there was also which paw the dog would lift up after effectively being asked to sit and give a paw; and lastly, which paw they led with while going down a single step.

Considering the data from all four tests, the team concluded that roughtly half of their dogs had a preferred paw, and the other half didn't. In other words, they were ambidextrous.

Now, you may have noticed that 32 dogs -

- 32 dogs isn't very many in the grand scheme of things, and small sample sizes like these aren't unusual for handedness studies, so it can be difficult to know if the patterns scientists do observe really reflect the whole species. But a meta-analysis in 2019 pooled together data from a number of smaller studies - both of dog's and cat-handedness - to get a better... grasp on these trends. 

And it turns out our feline friends have an even greater trend towards being righties or lefties than dogs. Over 75% of cats, compared to the 63% of dogs, demonstrated having a dominant paw. But that's just compared to being ambidextrous, and ultimately - at a species level - these pooled results show that cats are neither mostly righties nor mostly lefties. And dogs? Well, they seem to have a slight bias against being right-pawed, but that's all the researchers could say.

Still, there was one interesting pattern that turned up: Male cats were more likely to be left-pawed than females were, which is actually a pattern we see in humans. So, even if a species as a whole doesn't show a strong handedness bias, there might still be a lot of lefties and righties in their midsts. But pinning down these hand-habits in individuals can be a challenge in and of itself, because the hand you prefer to use may depend entirely on the task you're trying to do with it.

Take baseball switch-hitters, for example: While the majority of players only ever swing the bat from one dominant side - either right-handed or left-handed - some can bat pretty well from both sides regardless of their personal handedness. And for nonhumans, let's turn to our closest living relatives - the great apes.

In 2006, a paper summarized the results from a number of studies that looked at hand-use in over 1,500 individuals from four different species. And according to those results, both chimpanzees and bonobos showed right-hand dominance at a population-level.

- Meanwhile, the same couldn't be proven for either gorillas or orangutans. But a study from 2015, which involved hundreds of zoo-dwelling great apes from the same four species, showed that some tasks might just not work very well for measuring handedness.

When these individuals were tested for handedness by having them reach for and pick up pieces of scattered food, 51% of them didn't show a strong bias one way or the other. But of the apes that did show a preference, they were more likely to be right-handed, and that right-handedness became even more pronounced when the ape needed to use a precision grip - grabbing small foods like raisins and peanuts between their index finger and thumb.

But in a previous study, some of the same researchers had tracked handedness in a great apes another way - by observing how they held a tube in one hand and pulled food out of it with the other. In that test, which included many of the same individual apes, a whopping 80% had a preferred hand. Put this all together, and you can see just how much "which task you've chosen" matters when you want to hunt for handedness.

If one group of researchers is over there watching some apes pick up small objects from the ground, they might conclude something completely different than the researchers over there watching them dig food out of tubes. And if they can miss it in apes, they can miss it in our more distant relations. For species that do show strong handedness at a population level, right doesn't always dominate. To find some animal "southpaws," we just have to take a trip south of the equator.

A study from 2015 compared the behaviors of seven marsupial species - you know, those funky mammals typically known for their belly pouches that finish growing their itty-bitty babies. And unlike your typical lab-based experiments, researchers watched their day-to-day activities in the wild. This study also provided strong evidence that handedness didn't necessarily run in the family tree. Other factors such as posture were in play.

- posture were in play.

Red and eastern grey kangaroos, who spend more time kicking back on their two hind feet, appeared to be population-level lefties. But species that spent more of their time on all fours were not. For example, Goodfellow's tree-kangaroos spend about the same amount of time feeding on two legs as they do on four, and they didn't show population-wide patterns in handedness one way or the other. But, like we found in primates, some marsupial's hand preferences depend on what you're watching them do.

Red-necked wallabies were one species found to switch it up depending on the activity. If they were sitting on their hindlimbs while they ate, the majority showed a preference toward one of their forelimbs, and a majority of those handed wallbies preferred their left over their right - just like their bipedal kangaroo cousins and, you know, some of you out there. 

But when the wallabies weren't perched up on their hindlimbs or down on all fours and instead, sitting tripod-style, using an extra limb for more support - they turned into temporary righties - like any of us have had to do when pulling the wrong kind of scissors out of the art-supply bin. They're probably way less annoyed about it, though.

Now, I've been using the term "handedness" this whole time, but there's a more general term for preferring one side of the body over the other to complete certain tasks. It's called "lateralization," and it's how handedness can reveal itself in ways that don't have anything to do with the limbs, let alone hands.

Take whales: While they've technically got those hand-bones inside their flippers, they can't exactly pass the "grab-tests" we put primates through. But a long-term study published in 1995 that looked at hundreds of humpbacks showed that these whales were more likely to be righties when "flippering" - the act of raising a flipper out of the water and slapping it onto the surface.

But the researcher team also found a type of lateralization beyond the whales not-quite hands. All they had to do was look at a bunch of scuff marks or occasional scar tissue -

- scar tissue along the jawline. See, some populations of humpbacks are bottom feeders, scooping up their itty-bitty prey right along the sea floor. And it turns out, the whales that feed this way have a strong preference for one side of their mouth. Of the 75 jaws the team looked at, a whopping 80% showed abrasions on just the right side and the remaining 20% had abrasions on just the left - no ambidextrous bottom feeders in sight, or whatever the fancy-jargon term would be for using both sides of your mouth equally.

Putting those different behaviors together, the researchers revealed that if a whale was a righty-feeder, that also meant they were typically a righty-flipper-slapper, too, and vice-versa for lefties. But that's just one kind of whale. What about, say, the largest whale alive today and maybe throughout all of Earth's history?

While feeding on krill, blue whales will roll their bodies right before they open their ginormous mouths to chow down on some poor unfortunate krill. And according to a study from 2017, the direction they roll in seems to be tied to how deep they're feeding. The blue whales the research team monitored would perform a big barrel roll when feeding closer to the surface of the water, and in those instances, the majority of them rolled to the left. But when diving at deeper depths, they tried a different maneuver where they'd roll up to 180-degrees to one side and then roll back the opposite way. In those instances, the whales tended to start their side-rolls off to the right.

So, not only might different tasks affect whether or not scientists observe handedness or lateralization in certain individuals or species, the location that a task takes place in might, too. But wherever these whales may be hanging out, their fancy feeding tricks can show us how handedness works without ever lifting a finger.

And with that, we come to the final creature on our list, an animal that proves you can have a favorite limb even when you have -

- even when you have a whopping eight to choose from. At first glance, all of an octopus's arms appear basically identical, so one might assume they'll all be used in relatively the same way. But even with so many similar limbs, this doesn't stop an octopus from assigning certain tasks to certain appendages.

A 2006 study found that a group of eight common octopuses tended to use the four arms on one-half of their body for reaching out and exploring what's around them even though all eight arms would be capable of doing the exact same job. And individual octopuses also had one favorite arm that they'd prefer to use when reaching for food inside a test maze. Exactly which arm was the favorite varied between them, so I guess that's one way an octopus can express a little bit of cephalopod personality.

Then, there's a study published in 2022 which repeatedly tested the predatory behavior of ten California two-spot octopuses. After reviewing over 600 responses, they determined that they had a preferred arm for snagging prey - the second arm from the middle, otherwise known as [animation slide, arrow points] that one. Well, sort of. Unlike our "mammal-lefty/righty" tests, these octopuses didn't just have one dominant arm - they had a preferential pair - and precisely which second-arm they'll wind up using largely depends on which side of their body their prey is.

That's because their eyes aren't set up like ours. Each eye has a nearly 180-degree field of view, but there's essentially no overlap between them, so the octopuses end up approaching their target from one side or the other to get a good view. But, given the small sample sizes, we can't describe the full complexity of octopus-handedness just yet. It's certainly a challenge to study lateralization in nonhuman animals, but you really have to "hand" it to the scientists out there for trying, because we used to think it was an exclusively human trait.

And by looking at animals that are more and more distantly related to us, we can piece together how and why lateralization became a thing. Until we get those answers, at least we now know which arms you might not want to reach for when shaking an octopus' hand.

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