Across dozens of psychological traits, men and women mostly overlap
When psychologist Janet Shibley Hyde pooled 46 meta-analyses in 2005, she found 78 percent of the measured gaps between men and women were small or close to zero. Averages can differ while individuals overlap heavily: men are taller on average, yet plenty of women are taller than plenty of men.
Biologically, sex is usually set by whether the 23rd chromosome pair includes a Y. Some differences follow directly from genes on the Y, notably SRY, while others arise indirectly, often through hormones. Direct effects tend to fall into two categories, although complex development produces exceptions. Indirect traits typically form overlapping bell curves, so a gap in the averages says little about any one person, and the size of such gaps varies between populations.
The clearest contrasts involve reproduction: hormone systems, genital and breast development, muscle mass, height and body hair. Some brain regions also differ in average size. Medicine has its own pattern, with certain diseases confined to one sex and others skewed toward one; about 90 percent of primary biliary cirrhosis cases occur in women, while primary sclerosing cholangitis is more common in men. A field known as gender medicine studies how such differences affect illness.
Psychology is where interpretation gets hardest, because upbringing and expectations shape behaviour and even brain activity. Most IQ tests are designed to show no overall gap, and 2008 research found no significant difference in maths skills among schoolchildren from grades 2 to 11, though men appear more often at both extremes of IQ scores. Stereotypes themselves can change performance, an effect called stereotype threat. Among the larger measured differences, Richard Lippa found women leaning toward people-oriented interests and men toward thing-oriented ones, and Hyde's exceptions included throwing distance and some aspects of sexuality.
Disorders show a mixed ledger. A 1998 review of 80 adult diagnoses listed 35 as more common in men, 17 of them linked to substance use or paraphilias, 31 as more common in women and 14 as equally common. Brain research remains contested: a 2021 analysis reported no overall differences in verbal, spatial or emotional processing, while a 2022 meta-analysis challenged its methods and reported reproducible regional differences of small-to-moderate size.
Source: Sex differences in humans
