Natural history of the present

How a devastating famine favoured daughters and thereby illustrated an evolutionary point

China’s sex ratios are notoriously male-biased and becoming more so, but the worst famine in history created one tiny cohort in which almost as many girls were born as boys.

The following dramatic graph caught my attention the other day. It shows the sex ratio of babies to women in China between 1938 and 1982. The data came from a massive retrospective survey of the fertility of 300,000 women.

Royal Society of London

What staggered me, as it did Shige Song who wrote the paper in which the graph appeared, was the massive drop in the proportion of male births. Something happened in China in the early 1960s that massively changed the sex ratio.

That “something” was a famine - probably history’s largest. Between the end of 1958 and the start of 1962, the ill-conceived economic initiatives of the Great Leap Forward led to a China-wide famine that killed 20-30m people.

The famine also caused a precipitous drop in the number of births (see figure below), as women of child-bearing age starved and were unable to conceive or carry their foetuses to term.

Royal Society of London

These graphs imply a human tragedy so immense that it defies my ability to describe. But they also illustrate an important aspect of evolutionary biology that remains relevant even in the most modernised societies.

For my full article about the evolutionary forces acting on sex ratios, and the relevance of the Great Leap Forward Famine see the full article.