I came across a very interesting study after reading an article in this month's Parents magazine. The article said that handedness (left, right, or ambidextrous) and the direction of the whorl of your hair (counterclockwise or clockwise) are controlled by the same gene, and that people with a counterclockwise hair whorl (8.4% of population - that stat was not in the article - I looked it up later) have a 50/50 chance of being lefties/ambidextrous. I thought that this had to be a bogus article, so I looked up the paper and lo and behold, it is actually true. At least, after I read the paper, I was convinced. There is a more accessible article for the layperson that says the same thing (a review of the scientific paper) if you want to read that instead.
For the biologists out there, it works like this: R is the gene for being right handed and having a clockwise hair whorl, and it is dominant. r means you are a random recessive - it is unspecified whether you are left handed/ambidextrous or right handed, and it is unspecified whether your hair whorls clockwise or counterclockwise. RR individuals will be right handed, and will have clockwise hair whorls. Rr individuals will also be right handed, and will have clockwise hair whorls. rr individuals have a 50/50 chance of being right handed (and a 50/50 chance of being left handed or ambidextrous), and have a 50/50 chance of having a clockwise hair whorl (and a 50/50 chance of having a counterclockwise whorl). If you are a lefty, you MUST be rr, and if you have a counterclockwise hair whorl, you also MUST be rr. If you are a lefty, you have a 50/50 chance of having a clockwise hair whorl (and 50/50 of counterclockwise). If you have a counterclockwise hair whorl, you have a 50/50 chance of being left handed (and a 50/50 chance of being right handed).
Why in the heck are these genes connected? The author speculates that because skin (hair whorls are on the skin) and neural tissue (handedness is neurologic) both are derived from the embryonic ectoderm layer it is simple for them to be controlled by the same gene. Sounds reasonable to me, but still odd. Nature is pretty weird sometimes!
So why do I care? Well, turns out that BOTH Loren and I have counterclockwise hair whorls. Weird, since it's relatively uncommon. We both happen to be righties, but apparently we had a 50/50 chance of being lefties, as do both of our children. Calvin seems to be pretty darn ambidextrous, so I would not be surprised at all if he turns out to be a lefty or ambidextrous. As for hair whorls, Calvin's is counterclockwise and Michelle's is clockwise, as predicted by the genetic model.
EDITED 8/21 - Somehow last night I looked at Loren's hair wrong... he has a clockwise whorl. Calvin and Michelle are as reported, so Loren's genotype could be Rr or rr, since Calvin is clearly rr. Michelle could therefore be either Rr or rr, since her hair is clockwise. Interesting... we'll have to see how it all pans out.
2 comments:
Very interesting, especially as I am a leftie. One question...I have heard that 10% of the population is left-handed, but don't know how accurate that is. If your stat is correct that 8.4% of the population is rr, and therefore these 8.4% have a 50/50 chance of being lefties, the actual percentage of lefties would be only about 4%. Did the article say what the actual percentage of lefties in the population is? And if it's higher than 4%, I wonder how many lefties are actually Rr or RR...
It will be interesting to see how Calvin's handedness evolves!
Ah, yes, but you forget that some people with CLOCKWISE hair whorls are also rr. If you go back and look carefully, I wrote that 8.4% of the population has a counterclockwise hair whorl, not that 8.4% of the population is left-handed. The implication is that about 16.8% of the population is genetically rr, half of them w/clockwise hair whorls and half with counterclockwise whorls. Half of them will be right handed (8.4%) and half left handed (8.4%), so lefties will be almost 10% of the population, as you have heard.
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