h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"little evidence for a genetic link"
My cousins are forever having their blood taken for genetic testing and many male lefties with a male lefty brother have been asked for their blood. There are some interesting preliminary results, which imply a possible couple of genes which could be linked to lefthandedness, though it is still quite up in the air.

Take my family, it's a very famous one. I am a member of the clan Kerr. This clan is actually about 75% left-handers, both today and historically. Evidence for this shows in the left-handed defense staircases in our castles (spiral staircases have handed twists to give advantage to defending swordsmen), the lefthanded ways our kilts do up, so as not to interfere with the wearing of the sword and the traditional name in our neck of the woods for "lefty" - "kerr handed"

But I and a number of Kerrs I know, in past and present, have grown up in right handed families and yet we are still very very sinister and there are many instances of a single x-handed children in totally y-handed families which still display that opposing hand-dominance (where x and y may be right or left and vice versa.)

It is also interesting to note the way the brain works - the left hand side of a right hander's brain is bigger than the right hand side. It is the other way round for a lefty. Lefties and the close relatives of lefties also appear to be better at languages and/or to process language in a different way - different parts of our brains "light up" when tested with language - words and concepts and foreign languages (understood and not understood), both spoken and written.
[The tests are quite fun and it's really odd to see a video playback of ones brain lighting up in different places.]

Opposing the genetic argument:
There is also some archaeological evidence for a lack of bias in handedness until tools which were decidedly handed were developed, and even then it took a while for handedness to kick in. I'm a bit unclear on the exact details and I can't find the paper discussing this so can't give you the details.

Teaching and training into handedness:
Yes, teaching in the past has really often been to change the handedness, children often developing stutters and stammers and being more clumsy than their counterparts when treated this way. However this habit is decreasing and slowly parents and teachers are learning how to support left-handed children. I think that it will take a long time to see if this changes the proportions of lefties/righties because there are still people being forced to be righty today and there are a lot of people in older generations who were forced that way as children.

AEndr

I have a young deer on the end of each arm where my hands should be... Oh, wait, that's Bambidextrous...

AEender I think the best evidence against a genetic link is in identical twins, identical twins (exact genetic copies of one another)*are* more likely to have same handedness but if it was genetic then *all* (plus or minus a couple of percent,exceptions prooving the rule and all that)identical twins would have the same handed ness therefore there must be a strong social/developmental influence. What it is I have no idea, it will be interesing to see if levels of lefthandedness increase in the future now that there is no social stigma attached to handedness.

yes, sometimes I wish the future would hurry up to answer those "what will happen in x years time" questions. I especially wish I could be alive to see some of the answers...

I am completely ambidexterous. The hand that which I would use depends on the situation; I naturally will gravitate to whichever hand is more comfortable given the logistical layout of the environment in which I find myself.

hehe good one peet

I'm completely ambidextrous, and haven't met anyone else who is! I have two completely different handwritings that both look and feel equally fluent.

I am predominantly left-handed but have picked up some skills with my right hand and some with both.

The tooth brushing thing strikes me as odd though. I change my hands when cleaning my teeth - how would you get the brush into all the places at the back otherwise?