A series of four studies published in the Journal of Personality and Social Psychology examined the role of sex ratio on women’s family planning and career choices, finding that when men become a rare commodity, women gravitate towards high-paying careers and postpone starting families. In the late 12th century, a significant number of women in Northern Europe achieved economic parity with men, becoming independent entrepreneurs and forming labor unions. This shift was not due to government policy changes or social movements, but a demographic shift: a decrease in the ratio of men to women cre…