[Current aspects of handedness]

Area of Science:

• Neuroscience
• Human Behavior
• Genetics

Background:

• Behavioral lateralization, such as handedness, is a common trait in humans.
• Left-handedness, present in approximately 8% of the population, exhibits consistent incidence across cultures but is more prevalent in males.
• Understanding handedness offers insights into brain organization, particularly concerning language function lateralization.

Purpose of the Study:

• To explore the origins and contributing factors of handedness, with a focus on left-handedness.
• To review existing theories on the genesis of handedness, including genetic, socio-cultural, and pathological models.
• To investigate the evidence for genetic versus environmental influences on handedness.

Main Methods:

• Review of existing literature on handedness and behavioral lateralization.
• Analysis of various handedness assessment techniques, including preference and performance tests.
• Examination of family, adoption, and twin studies to infer genetic and environmental contributions.

Main Results:

• Left-handedness is more common in males than females.
• Language dominance in the cerebral cortex differs between left-handed and right-handed individuals.
• Family and adoption studies suggest a genetic basis for handedness, though monozygotic twin studies show discordance, indicating environmental influences.

Conclusions:

• The etiology of handedness, particularly left-handedness, is complex.
• A polygenetic model incorporating environmental factors is likely required to fully explain handedness.
• Further research is needed to elucidate the interplay of genes and environment in determining handedness.