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23 July 2004
Handedness appears to be set
in the womb at just 10 weeks gestation, and not at 3 or 4
years of age as previously believed,
say UK researchers who studied 1000 fetal ultrasound scans.
The team, led by Peter Hepper from Queen's University in Belfast,
observed that nine out of 10 fetuses at 15 weeks' gestation
preferred to suck their right thumbs, a proportion similar
to the prevalence of right-handedness in adults.
They followed-up
75 of these fetuses at age 10-12 years, and found that all
60 right-thumb suckers remained right handed, while two thirds
of the left thumb suckers still preferred to use their left
hand.
Moreover, at just 10 weeks' gestation, before they suck
their thumbs, the fetuses wave their arms around, and Hepper
et al noted that the majority waved their right arm more than
their left, and that this preference persisted until 24 weeks'
gestation, when they no longer had enough space in the womb.
As the brain is not thought to control body movements at 10
weeks' gestation, the researchers suggest that the motions
are controlled by spinal cord reflexes and that the inequality
may be set because one side of the body develops slightly faster
than the other.
Source: 4th Forum of European
Neuroscience: Lisbon, Portugal; 10-14 July 2004
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