AFTER just 10 weeks in the womb, human fetuses already show a striking right
or left-handedness, say scientists in Northern Ireland. They say the finding
could mean that, contrary to the conventional idea that the brain directs
handedness, the opposite may be true: handedness may direct the way the brain
develops.
Glenda McCartney and Peter Hepper at Queen鈥檚 University of Belfast used
ultrasound to watch the earliest hand movements of 87 young fetuses, typically
at around 10 weeks鈥� development, to see which hand they moved most. It turned
out that about 85 per cent of the fetuses were right-handed鈥攋ust as in the
adult population.
To check whether this pattern changed in later development, scientists also
scanned 17 fetuses at three-week intervals between weeks 12 and 27. This
confirmed that once hand preferences are established, they stick.
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The arm movements occur so early in fetal development that the brain hasn鈥檛
begun to control movement, Hepper told last week鈥檚 meeting. Instead, the
flailing hands are probably just a result of reflexes, he says. 鈥淭here is no
possible role for the brain at this early 蝉迟补驳别.鈥�
The findings may stand conventional theory on its head. 鈥淲hat we鈥檙e
suggesting is that perhaps differential arm movement leads to differential brain
growth,鈥� says Hepper. 鈥淢ovements cause brain specialty, and not the other way
补谤辞耻苍诲.鈥�
Marion Annett, a developmental psychologist at the University of Leicester,
is not convinced, however. 鈥淚 think it鈥檚 a very interesting finding. But I don鈥檛
think it necessarily follows that the hand influences the brain,鈥� she says.
鈥淭his research is telling us that something is asymmetrical at a very early
蝉迟补驳别.鈥�
Hepper now hopes to look more closely at what causes the early handedness.
His previous work on hand preference in thumb sucking rules out the position of
the fetus in the womb as a major influence. Some combination of genes may be
responsible instead, he says.