As we all know, humans have a dominant hand (and foot, and eye) that we prefer to use; my question is, why? Why do humans prefer one over the other? What benefit do we get from having a dominant limb? Is there any benefit? Why didn’t we (evolutionary-wise) just use which ever limb was convenient at the time?
Because if you tend to do a task with a particular hand (as opposed to randomly using either hand), you’ll become proficient much faster. This helps when chucking spears at mastodons or filling out credit card receipts and whatnot.
Or so goes the theory.
I’ve read from multiple sources (including cecil!) that other animals are evenly split 50-50.
There are many theories for why humans are different than animals. One of these is that the greater developement of the left-side of the brain encouraged humans to be more right handed since your brain controls the opposite hand.
Another theory is that language was signed before it was spoken (babies can learn sign language long before they can learn to actually speak). The right hand was favored in gestures (since language is on the left side of the brain) and therefore, people who had better control of their right hand/used it more were dominate. More on that here.
Handedness is important because specilization is better than generalization as far as motorskills go. Chimpanzees that are pridominately right- or left-handed are more skilled at fishing for termites than those that are equally skilled in both hands.
Hope that helps.
My stepfather worked at NASA for many years, and I once asked him (can’t remember how the subject came up), “Does NASA prefer people with ambidexterity, since all those switches in the Shuttle are all over the place?”
He said that NASA specifically avoids the ambidexterous, because they have to hesitate a split second to, say, flip a switch, to decide which hand to use- while righties and lefties don’t have that delay.
Dunno if it’s true, but it sounds true.
Chimpanzees can be either right- or left-handed.
With most other animals, though, it’s going to be tricky to tell. Could a beetle or a cat be left-handed?
My cat nearly always uses her right paw to grab or bat at things. I’d say she’s right handed.
D’oh, the first part of my answer got cut off. I had said that humans are 90% right handed and about 10% left handed.
The animal part was supposed to mean that animals are about 50% right handed and 50% left handed.
Sorry for the confusion.
That’s an interesting link, ava. So our dominant-handedness may be linked to language, eh? Curiouser and curiouser.
You shouldn’t assume there’s any reason. There may very well be of course, but there doesn’t have to be. Handedness may be an unintentional consequence of some other adaptation. As long as it’s not actually detrimental, it wouldn’t be selected against.
Humm - this sounds true to me as well, and I’m ambidexterous. I developed writing skills later than my peers, but I can write with either hand - however, it always seems like I’m the last one to finish taking down notes in class.
Of course, this could be because I’m just slow, also.
The only advantage I’ve ever had is shooting pool - I can shoot with either hand, and while this only marginally improves my pool game, it is effective in meeting members of the opposite sex. (Again, I dunno what advantage being ambidexterious would have in the romance department, but I think fellas must think it would)
I wonder how much of the brain is devoted to fine motor control of the hand. Since there’s so many bones and muscles in the hands, and so many ways to move them, I would imagine a huge portion of the part of the brain that controls movement is devoted to the hands.
If that’s the case, than it would make sense for only one hand to have such fine motor control. Given that every increase in brain size makes childbirth more dangerous, and since the head is a huge energy cost in humans, then having somewhat less motor control in one hand may allow for greater motor control in the other without increasing the ‘brain tax’ on fitness.
This is of course a WAG, but if you only have so much skill to dole out, making one hand more skilled than the other might make perfect sense. Since you’re only likely to be engaging in one fine motor activity at a time, the other hand can be relegated to a supporting role while the dominant hand gets first billing. That way, you have more ability when you need it.
You sure about that? Looks to me like Cecil is saying that most animals have a side preference, and that in some (including cats), there’s a bias within the species towards one side or the other. He also describes an experiment for determining paw preference in cats, and offers the “more practice with one paw” explanation several Dopers have mentioned here.
Good point.