evolutionary biologists mostly assume that polygyny increases sexualdimorphism in size because, under polygyny, larger males monopolizemating opportunities and pass on their ‘large male’ genes to theirsons. available data on parent–child correlations in height amonghumans (homo sapiens) do not support the crucialassumption that height is transmitted along sex lines. this paperinstead suggests that human sexual dimorphism in size emerged, notbecause men got taller, but because women got shorter by undergoingearly menarche in response to polygyny. it further speculates that,rather than genetically transmitted, the sexual dimorphism mayemerge anew in each generation in response to the degree of polygynyin society. the analysis of comparative data supports the predictionthat polygyny reduces women’s height, but has no effect on men’s,and is consistent with the speculation that the origin of humansexual dimorphism in size may be cultural, not genetic.