Greater Intrasex Phenotype Variability in Males Than in Females is a Fundamental Aspect of the Gender Differences in Humans

Human studies of intrasex variability have shown that males are intellectually more variable. Here we have performed retrospective statistical analysis of human intrasex variability in several different properties and performances that are unrelated or indirectly related to intelligence: (a) birth weights of nearly, 48,000 babies (Medical Birth Registry of Norway); (b) adult weight, height, body mass index and blood parameters of more than 2,700 adults aged 18-90 (NORIP); (c) physical performance in the 60 meter dash event of 575 junior high school students; and (d) psychological performance reflected by the results of more than 222,000 undergraduate university examination grades (LIST). For all characteristics, the data were analyzed using cumulative distribution functions and the resultant intrasex variability for males was compared with that for females. The principal finding is that human intrasex variability is significantly higher in males, and consequently constitutes a fundamental sex difference. (C) 2008 Wiley Periodicals, Inc. Dev Psychobiol 51: 198-206, 2009.