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The Endowment for Human Development
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Right- and Left-Handedness


8 weeks

From The Biology of Prenatal Development.Buy Now

Script: By 8 weeks, 75% of embryos exhibit right-hand dominance. The remainder is equally divided between left-handed dominance and no preference. This is the earliest evidence of right- or left-handed behavior.

All ages referenced to fertilization, not last menstrual period.
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Ovaries Identifiable
Ovaries Identifiable
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The Highly Complex Brain
Right- and Left-Handedness
Right- and Left-Handedness
Rolling Over
Rolling Over
Spontaneous Movement
Spontaneous Movement
Reflexive Movement
Reflexive Movement
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