05

As the attentive reader has noted, higher sex ratios would trivially raise the crime rate
if men are more crime-prone than women, since a higher sex ratio implies more men (per
capita). However, assuming that average male propensity to commit crime was unchanged,
it is easy to see that a one percent increase in the fraction of men could at most result in a
one percent increase in crime. In fact, the elasticity of crime with respect to the sex ratio
exceeding 0.5 would indicate that crime rose not only because of more men, but also because
men became more crime prone (see derivation in the Appendix).
Our estimated elasticities are well above 0.5 and thus support the more interesting proposition
that crime rose not only because of more men, but also because men got more crime
prone. This raises the question why male sex ratios would have this effect. While there
are several possibilities, e.g., peer group effects, marriage market related mechanisms seem
first order (if only for the fact that if it were not for reproduction, sexes would be of little
relevance). High sex ratios imply