Wednesday, October 05, 2011

Hair whorls and womb twin survivors


What is a hair whorl?

The hair whorl is the way that the hairs on our head grow across your head from a single point at the back of your skull.  Hair whorls can develop clockwise or counter clockwise (see here)  in the USA counterclockwise hair whorls are very rare.
In people with short, straight hair, a single whorl is usually fairly obvious. Clockwise whorls are most common; estimates of the frequency of clockwise whorls range from 51 percent in Japan (Klar 2009) to 65 percent of undergraduate psychology students in the United Kingdom (Annett 1985), 69 percent of Nigerians (Ucheya and Igweh 2005), 74 percent of German schoolboys (Bernstein 1925), 81 percent of students in the United States (Lauterbach and Knight 1927), 92 percent of the "general population" in Maryland (Klar 2003), and 94 percent of newborns in the United States (Wunderlick and Heerema 1975)
Counter clockwise whorls go with left handedness, and left handedness, like hair whorls, varies between countries.  Left handedness is related to mirror MZ twinning.  So are people who are not twins but have counter clockwise hair whorls womb twin survivors?  I wonder.


The double hair whorl - what causes that?

The double hair whorl is more common among twins than among singletons.


An article in the Journal of investigative dermatology, no less, described an unusual case of MZ twins, who had different hair whorl patterns.


It seemed to the investigators that these MZ twins, who shared the same genes, could have different hair whorls if this was a genetic effect.   But of course they didn't have the benefit of knowing about womb twin survivors, and in particular how a pair of live-born twins could have started as triplets.  This idea is enough to completely confound all twin studies!

It seems possible to me that the MZ twin with the double hair whorl had a monzygous twin of his own, lost a long time before birth. These twins did not share a placenta, so the zygote split apart very soon after conception.  Over the next few days one of these could have split again, but only one twin made it to birth. Useless therefore to say that this is a genetic effect, when it mechanical - to do with the splitting of the zygote.


Very clear with short dark hair















Not so clear on longer grey hair ( this is mine)









Now research has shown that "double crowns" go with left-handedness, but I am very strongly right handed, so what about that? Well I do think I had an identical twin, lost very early, who never got off the ground but left her mark on my head! It is the MZ twinning in my intrauterine life that has created the double whorl on my head.

That's my theory, at least for the moment.........

Any thoughts, anyone?

5 comments:

  1. This is pretty interesting. I'm left handed, and have something resembling 2 hair whorls. My younger brother is RH, and definately has 2. Our grandad was a LH twin (his sister was RH). I wonder if this is all linked? I've always felt as if I shoud have had a twin- I wonder if my brother should have had one too?

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  2. After reading this I of course had to look at my whorl. (-: I knew where it was but somehow it's not very round and 'only' one. When I looked right it's clockwise, while it's 'supposed' to be counter clockwise because I'm left handed.

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  3. We have 6 members of the family .. Mom & 2 kids have double crowns and are all RH

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  4. I am left handed and have a double crown. What is very strange is I have always felt I was a twin. Interesting but not really prooven to be a fact.

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  5. I use my right hand but have long suspected maybe I'm not entirely right handed. I have three kids, one of whom is left handed. I and all three kids have double crowns. Mine both seem to go counterclockwise. My kids' go in opposite directions.

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