6 upvotes, 2 direct replies (showing 2)
Most mammals like dogs and cats do show paw dominance, but it seems to be about a 50/50 split in their case. Whereas in humans about 90% of humans are right handed. Twin studies have show that it is most likely genetic however the specific genes have not been pinned down. Two right handed parents can have a left handed child, but if a child has a first degree relative who is left handed they are more likely to be left handed. This suggests it's a recessive trait.
The reason why right handedness seems to dominate humans probabaly has to do with tool use. As we adapted to use tools, we built tools to be used with a specific had. Over time, one hand randomly became selected over the other. That just happened to be the right hand. There's no reason the right hand is better, but having most people in your species able to use the same tools with the same hand is advantageous. The right hand just happened to be randomly selected. In an alternate timeline it could just have well been the left hand and we'd be living in a world where 90% of humans are lefties.
But hand/paw dominance is a trait seen in nearly all animals. This is due to reinforcing neuro circuits. It's easier for the brain to focus on making on hand/paw extremely dexterous and having the other just be the helper, because for most two handed tasks you only need one main working hand and one stabilizing hand. It's simply saving brain power.
Comment by curien at 29/06/2017 at 16:01 UTC
3 upvotes, 0 direct replies
Twin studies have show that it is most likely genetic however the specific genes have not been pinned down.
The thing is, we'd expect *any two randomly-chosen people* to be discordant just over 19% of the time (based on left-handed prevalence of 10.8% as reported by Wikipedia). But MZ twins are actually left-handed slightly more often than the general population, at 14.5% (ibid). Standard probability for two randomly-chosen MZ twins to be discordant would be just under 25%.
I.e., it doesn't appear -- based on rates I've seen -- that MZ twins share same-handedness any more than we'd expect by completely random chance.
Comment by HalfPastTuna at 29/06/2017 at 20:40 UTC
2 upvotes, 1 direct replies
Is being ambidextrous fitness negative in any sense? Does it require more energy to power an ambidextrous brain/nervous system?