Also fun fact, kangaroos have this same 90-10 split: https://www.nationalgeographic.com/animals/article/150618-ka...

Over the years, I (and I imagine many others) switched over to WASD to play newer games with mouse + keyboard, but this meant using the left hand for "arrow keys"

Now I can directly compare how proficient I am with WASD vs Arrow Keys and the result surprised me. I was way worse with arrow keys (right hand) even though back when WASD was becoming a thing I'd rebind WASD to arrow keys because it felt too weird! I would've never imagined back then that WASD could ever feel as natural as arrow keys.

Makes me wonder how much of handedness is truly innate vs learned.

1. Some schools actively punished children for writing left-handed.

2. Pretty much every utensil was made for right-handed people. I don't recall ever seeing left-handed scissors, for example.

3. You learn by copying those around you. If your parents, teachers, and peers are predominantly right-handed (and are even actively encouraging you to be right-handed), then you're likely to toe the line.

I imagine the final point would remain a factor long after the first two are addressed.

The question from the headline is excellent, if only it was actually answered.

In particular, I would expect the influences to be somewhat counter intuitive. With things like having to use the left hand to hold a caregiver's hand in early walking preferencing the right for accessory use. At infant ages, it would be neat to see if preference of holding a baby on a side influences things.

If a baby sleeps better, it cries less. If it cries less, it attracts fewer predators and helps both parents sleep better at night and have more energy. It also allows the mother to do things with her dominant hand if she is right-handed.

Given the left-handed cradling bias exists even with left-handers, it means there is something specific with left-handedness and infant rearing. A baby in the left hand and a tool (or weapon) in the right is biologically efficient.

Most studies take this from the perspective of evolutionary advantage of the individual. They should take it from the perspective of evolutionary advantage of the family, without which the baby does not survive.

If the bias confers evolutionary advantages, that is also important for the longer childhood humans have compared to primates, which supports our larger brains. Any differential here would have a feedback effect.

Wouldn't it be interesting if a key reason humans are the way we are is a mother's love ♥?

[1] https://sites.psu.edu/clarep/2024/04/12/the-left-cradling-bi...

I've been told that it's effectively a mental illness if discovered during childhood (as is ambidexterity). Yet I can't help but think that it is not a mental illness, but rather something else.

I can walk a bicycle perfectly just by holding nothing but the saddle with my right hand. I can pick some spot on the ground ahead, call it, and hit it with the front wheel accurately.

Switch to my left hand and the bike's front wheel starts having a mind of its own.

"No, don't veer that way, Bike; you're not reading my mind, like you do through my right hand!!!"

Australopithecus was already strongly lateralized — committed handers — long before the rightward consensus emerged. Two traits, evolved separately by millions of years.

I kick with my left foot too. I feel more comfortable throwing with my right. If I'm holding a bat, I do so the "normal" way (idk terminology there).

When my son was learning to write I was super excited that it looked like he would be a lefty but a week later he favored his right hand for scribbling.

As younger people start using computers they generally will learn with right-handed mice and will thus develop those fine motor skills in that hand. I wonder if this will make right-handedness even more dominant.

"There are no left-handed in China" might sound as ridiculous as "There are no gays in Uganda".

However of those thousands of students, none had messy hand writing. In any class in Europe or the US, around 10% of students have messy writing. Suspiciously equivalent to the supposed number of left-handed students.

But since the middle of the continuum, i.e. no-preference, would presumably be the worst situation, it would be developmentally unstable and any tilt to either side would quickly become dominant.

One possible "motive" for a particular left-right lopsided bimodal skill pattern.

Twins are slightly more likely to be left handed, might be something to do with crowding in the womb where a specific hand is free more than the other.

>Using the same models, the team was also able to estimate likely handedness in extinct human ancestors. The picture that emerges is a gradient [from less handedness to more as time goes on]

"we explored the data until we found a statistical anomaly and it implies X" may be interesting[1], but there are TONS of those that are NOT true. is there supporting evidence for this, or is it just "hey this math says maybe"? it sounds more like the latter (as it quite literally seems like they're claiming roughly "big arm + big brain = big handedness", both in this site and in the paper itself), in which case they might also be interested in this study that pirates keep the global temperature down: https://www.forbes.com/sites/erikaandersen/2012/03/23/true-f...

1: from skimming the methodology in the paper, I honestly think this may be a fair characterization. it sounds like they combined data columns until one combo came up as P>0.95 and didn't have counter-evidence and said "that means it's probably true". but also some (all?) of that data may have been generated by models they created based on real ape data (I think?), which just sounds even more sus.

For hands, it is completely irrelevant how many legs a human has, regardless if a human had used 2, 4, 8, 14 or any other number of legs for walking, the hands would have become specialized.

The reason why the hands acquired specialized roles was that they were no longer used for locomotion, i.e. for brachiation in the trees, like in orangutans or gibbons, but their purpose became holding, controlling and moving various objects from the environment.

It is wrong to say that bipedalism has freed the hands to be used for other activities than locomotion, because the causality was reverse, locomotion became restricted to the hind legs, because the hands were used for other activities, like throwing sticks and stones, so they were no longer available for locomotion.

The strong specialization of the 2 hands has appeared because in most cases when something is transformed with the hands, e.g. bones are broken to get the marrow or stones are knapped to get a cutting edge, one hand must be used to fix in place the object that is processed, while the other hand must move against it, normally with some tool.

For the former role, the left hand became specialized, while for the latter role, the right hand became specialized.

Similar specialization is also seen at other animals where a pair of legs is no longer used for locomotion, but it is used for manipulation, for instance at crabs and lobsters.

So there is no doubt that the specialization of the hands was a necessity when they stopped being used for locomotion. However, it is not known why the right hand became the moving hand and the left hand became the holding hand, and not vice-versa. It could have been a random event or it could have been related to the asymmetry in the locations of the unpaired internal organs, like heart, liver, stomach and so on.

Paraphrase: Amongst primates there is a correlation between brain size and bipedalism with handedness… (unless you exclude humans, in which case there isn’t.)

That’s like saying: “Alongst animals there is a correlation between height and neck length… unless you exclude giraffes, in which case there isn’t.”

If a correlation disappears when you remove one datapoint, then the correlation was not really a broad pattern across the dataset. It was mostly a story about that one datapoint.

I mean, I get it… you gotta publish something. But, geesh… this is beyond stupid.