Cited research: Am. Nat. doi:10.1086/652470 (2010)

If natural selection favours the fittest, a population's genetic variance should decline over time. Yet many species adapt to changing environments, so variation must persist.

Caitlin Dmitriew at the University of Toronto in Canada and her colleagues investigated this paradox by putting some larvae of the ladybird beetle (Harmonia axyridis) on a restricted diet while giving others plenty of food. They found that the amount of variance in body size attributable to genetics decreased within a generation in well-fed male beetles, but increased in rationed ones. With enough food, the beetles converge towards an optimal adult size, masking the underlying genetic variation in body size. In hungrier beetles, body size varies more.

The accumulation of such 'hidden' genetic variance when times are good could explain how organisms retain the variation they may need when the good times turn bad.