A Role for the X Chromosome in Sex Differences in Variability in General Intelligence?

Area of Science:

• Behavioral genetics
• Neuroscience
• Developmental psychology

Background:

• Substantial evidence indicates males are more variable than females in general intelligence.
• Males are overrepresented at both extremes of the intelligence distribution, despite minimal mean sex differences.

Purpose of the Study:

• To investigate the role of X chromosome genes in sex differences in general intelligence.
• To model the population distribution of general intelligence and explore sex-based ratios.
• To estimate the contribution of X-linked genes to intelligence variance.

Main Methods:

• Developed a mixture model of general intelligence distribution.
• Analyzed the overrepresentation of X chromosome genes in mental retardation.
• Explored expected male-to-female ratios across the intelligence spectrum.

Main Results:

• Genes on the X chromosome are implicated in both mental retardation and normal intelligence variation.
• The X chromosome appears overrepresented among genes associated with mental retardation.
• Estimated the proportion of intelligence variance potentially attributable to X-linked genes.

Conclusions:

• X chromosome gene distribution may explain sex differences in intelligence variability.
• Biologically based sex differences in genes can influence displayed intellectual abilities.
• Findings contribute to understanding sex differences in cognition and evolutionary sexual selection.