The genetics and evolution of handedness

Area of Science:

• Evolutionary biology
• Human evolution
• Genetics

Background:

• Handedness and cerebral lateralization for speech are complex human traits.
• The genetic basis for strong right-handedness and left-hemisphere speech dominance remains debated.
• Previous hypotheses have not fully explained the stability of handedness proportions.

Purpose of the Study:

• To propose a genetic model explaining the evolution of human handedness and speech lateralization.
• To investigate the potential role of a single gene mutation in establishing dextral bias.

Main Methods:

• Population genetics simulations were employed.
• The spread of a hypothetical 'dextral' (D) allele was modeled.
• Reproductive fitness advantages for heterozygotes were analyzed.

Main Results:

• A single 'dextral' (D) allele mutation could rapidly spread through a hominid population.
• A slight reproductive advantage for CD heterozygotes over CC and DD homozygotes explains allele fixation.
• This model accounts for the stable ratio of left-handers to right-handers.

Conclusions:

• The dextral (D) allele likely emerged 150,000-200,000 years ago with Homo sapiens in Africa.
• This mutation strongly biased handedness and speech control, shaping human brain lateralization.
• The heterozygote advantage of this allele maintains stable handedness proportions in modern populations.