Humans have spread to occupy most of the world, but the genetic consequences of this demographic expansion are not known. Moreau et al. (p. 1148, published online 3 November) examined the expansion of colonies in Quebec from 1686 to 1960, on the basis of church registries. Individuals on the wave front had significantly higher fitness (reproductive success) than those within the core of the population. Women on the wave front married on average 1 year earlier than those in the core, extending their reproductive potential, and wave front families would have experienced greater availability of land for offspring, relative to those within the core.
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