Not being right-handed seems to be a risk factor for a huge array of disorders:
Well, then you’d have to explain why most parrots are lefties (really, they are).
Apparently having a dominant hand is advantageous in some manner, and it may be that which side was normally dominant was a matter of chance in a distant ancestor, and that handedness has been passed down to us.
Hello Broomstick, 
How can you tell that parrots are left-handed? Do you mean that they always stand on one foot and eat by picking up food with the other foot? I’m not sure which foot you would call “dominant”.
But that’s very interesting. I had a parrot for ten years and I never noticed that she always ate food I gave her by holding it with the same foot.
She hated the store-bought bird food and would make a huge ruckus unless I fed her by hand. She always insisted on eating only the same food that I ate. But I never minded. I loved to feed her by hand. Her favorite food was pizza. Believe it or not.
Not always but according to my (admittedly not exhaustive) research most parrots prefer picking up/holding/manipulating things with one foot over the other. My conures have both definitely favored their left foot for this. The three cockatiels I’ve had don’t seem to pick up/hold/etc. much of anything and if they had a preference I’ve never been able to figure it out. The lovebirds were less inclined to use their feet as hands than the conures but all three seemed to favor the left when they did such things.
Informal browsing turns this up as a frequent observation, that parrots tend to be left-dominant. It’s not as strong as in humans, but it does show up statistically.
Not all parrots have a dominant foot, and even those that do tend not to be as preferential as humans.
I should probably point out that avian brains are structured very differently than mammalian brains, and that might well account for some of the differences here. Which is why I speculate that handedness might have have an advantage, but which hand is preferred may be due to random chance in an ancestor. Humans might have had that ancestor as a righty, birds like parrots might have had a lefty in that position.
Most mammals (again, informal research) don’t show a preference for one hand over another. The great apes (chimps, gorillas, orangutans) show some tendency towards a dominant hand, but which hand seems a bit random and there are plenty who don’t show handedness. Chimps and gorillas might be slightly more inclined to be right handed, and orangutans slightly more likely left handed but the evidence is weak at best from what I’ve seen.
It might be (note all the qualifications indicating speculation here - it’s all over what I’ve found on the subject) that preferring one hand over the other makes you a better toolmaker/user, in which case the strong tendency to favor one hand makes a lot of sense in humans, but doesn’t account for being right handed so frequently as opposed to left. It might account for handedness in parrot species that frequently grasp/manipulate objects, in that specializing with one leg for grasping a perch/supporting the body and the other for finer manipulations also makes sense, for similar reasons as humans, but again which hand is preferred is not accounted for.
Crows also show a preference in such matters - let’s get more formal and call it “lateralization” which gets away from “hands” and towards “whatever the critter manipulate with or favors”. New Caledonian crows are also tool users and makers and also show a lateralization preference - with most being righties! At least when they’re making tools. Here’s a bit more on handedness in animals
So… apparently lateralization appears in species that make/use tools and might have something to do with brain organization. Which side is favored seems a bit of a crap shoot, but the more a species makes and uses tools the more likely the majority will favor one side or another.
Bottom line: it appears to be connected to tool making and use, and since humans are so specialized in that role it makes some sense we’d have strong lateralization.
That’s probably the likely explanation. We learn a lot of tasks (motor skills) by repetitive training until it becomes instinctive. By using the same hand every time, we learn the task faster and get better at it, until it just “feels right”.
One explanation I recall reading (obviously someone being somewhat sarcastic) was that left-handedness was the brain development compensating for oxygen starvation and brain damage during birth.
Nature? NatGeo!? Okay that’s it, turn in your Dope card (you got one, right?). Here’s a credible cite. 
Anyone want to hazard a guess as to why I’m right handed but left footed? From my earliest memories, it always felt more natural to kick a ball with my left foot.
While left-handedness can be a compensation for damage (people who lose their arm or are paralyzed by a stroke can learn to use the non-dominant hand for tasks that used to be done by the now missing or useless hand) it’s not always. There are developmental situations where all the internal organs are a mirror image of the usual arrangement, and such people are, not surprisingly, frequently left-handed. That’s not damage, that’s a reversal of some early signal in the embryo.
If a lefty’s brain is arranged more as a righty’s that might be a case of damage compensation, but if the lefty’s brain is a mirror image of the typical righty’s I’d suspect it’s a developmental reversal of some sort (not everything has to be reversed. Pre-birth development can be complicated). We can actually make such determinations in a living brain. When my mother (a lefty) had a stroke they did imaging that showed her brain organization was mirror to the typical righty’s (which was fortunate, because if it wasn’t the stroke would have been far more damaging than it was). The doc’s said it was important to know these things when planning for rehab. They also said that you occasionally find a righty with a “mirror” brain, that is, their brain is a mirror image of a typical righty, which means in that case being right-handed might be a case of pre-birth damage compensation in someone who should have been a lefty!
Read Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures.It has all you need to know…
Prefering to have a sexual partner is a disorder?
But if you write in the sand with your toe, which foot do you use?
No, really. I catch and throw equally well (which is to say not very) with both hands, iron only with my right hand (even with irons with the cord in the center), sew and saw only with my left, cut with the left but stir with the right, cut in with my left hand and paint with my right, brush my teeth with the left but lather and loofah preferentially with the right …
But by foot or by hand, I alway write with my left.
Maybe you balance better on the right leg.
[And most of my dogs have been right pawed]
pssst, I know it isn’t really germane to the main discussion, but, they will provide you with adeflector or catcher if you bug your platoon sgt and/or supply sgt long enough and fill out the paperwork enough times, at least in the US army anyway.
Allegedly, when I was a baby I showed a left preference, but was trained to be right-handed to fit in with the majority. Subtly not forcefully, and from the very beginning. Some of the alleged physical indicators (finger length, etc.) support this. :dubious:
Possibly as a result, I tend to have less of a hand preference than most people I’ve met. I eat “British style” when it has a lot of cutting or if my right arm is restricted, “American style” when it involves a lot of scooping, and never consciously think about which one.
I “mouse” with my left, but use a right-hand mouse - to me mousing is an inherently left-handed activity (leaves your right free for the keyboard, and you can have the main QWERTY keyboard aligned with your monitor more easily.) :rolleyes:
I’ve noticed I have a tendency to use my left for activities with a higher probability of hand injury - without conscious thought of it.
Basically, things with a high degree of fine motor skills go to my right hand, medium levels have a habitual right tendency but can be done either way, and low skill activities are whichever hand is easiest.
Although there are some exceptions - grey whales are mostly right-handed -flippered -mouthed, we know this from imaging their feeding dives and observing the relative wear on the right-versus-left sides of their heads.
Much handedness may indeed be related to tool-use, but other forms of manipulation of the environment may be important to the exceptions.
It depends:
I know I don’t want to read that thread.
On preview: NOT a reply to the left-handed pedophilia thread. I’m pretty sure I stayed away from that mess.
That is an old fashioned prejudice. The idea that left hand people are ‘awkward’ comes from the fact they have to use right handed objects. Many right-handed people don’t realise how difficult this is.
Try these:
-
Ask people to write backwards. Left handers are much better then right handers for two reasons: first, they backward direction is (at last!) in their favour. Second, left handers are used to adapting, not copying, hand movements.
-
Give a righty a left-handed corkscrew and watch them struggle!