This SciShow list-show, is supported by LMNT.
You can head to D-R-I-N-K-L-M-N-T dot com/scishow
for a free sample pack with any order. 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 5 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 percent 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 dogs 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 roughly
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 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 dogs 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 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
showed 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 handed 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 non-humans, 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 1500 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 food like raisins and peanuts between their index finger and thumb.
But in a previous study, some of the same researchers had
tracked handedness in 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.
Red and eastern gray 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’ve found in primates, some marsupials’ 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 wallabies 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 tri-pod 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 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 while flippering,
the act of raising a flipper out of the water and slapping it onto the surface.
But the research 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, along the jawline.
See, some populations of humpbacks are bottom feeders,
scooping up their itty bitty prey right along the seafloor.
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 may be throughout all of Earth 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 a whopping eight to choose from!
At first glance, all of an octopus’s arms appear basically identical.
So one might assume that 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 preferred 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 10 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 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 degrees 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 non-human 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 both how and why lateralization became a thing.
Until we get those answers, at least now we know which arms
you might not want to reach for when shaking an octopus's hand.
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