Link: Selection for tall Dutch men

Carl Zimmer comments on a new paper that shows that the exceptionally tall average stature of today’s Netherlands population has been augmented by natural selection during the last fifty years: “Natural Selection May Help Account for Dutch Height Advantage”.

Among those born in the early 1950s, for example, men who were 5 feet 6 inches had on average 2.15 children. Men who were 6 feet 1 inch had 2.39 children. The scientists found that the trend toward taller men having more children persisted for more than 35 years.
Among women, the pattern was more complex. Over all, Dutch women of average height had the most children. But that was because taller women tended to take longer to become mothers. Once they entered their childbearing years, taller mothers had children at a faster rate than shorter women.

Zimmer makes a brief reference at the end of the article to a population in Massachusetts where the evidence goes in the opposite direction. This is the long-term Framingham Heart Study, in which shorter women have consistently shown larger family sizes than taller women. It does seem remarkable that different industrialized nations actually have experienced selection in opposite directions during the last fifty years.

The levels of selection are not small: the difference in lifetime fitness between tall and short Dutch men is more than 10 percent. The change per generation will be lower, because (1) women do not show the same fitness difference, (2) the heritability of stature is around 0.8 or so, and (3) it depends on the distribution of fitness across the population, not just the difference between tall and short classes. But still, 2 or 3 percent of stature per generation is strong selection. Over many generations, that kind of difference would result in a large and rapid change. Of course, without knowing the cause of selection—social dynamics? sexual selection? correlation with some other selected trait?—we can’t predict whether the selection will be maintained in the future.