Aligning the Loops

A study published in the journal Biology Letters finds that the evolutionary advantages and disadvantages of being a specific height are unevenly distributed between the sexes. For women looking to pass on their genes it is better to be short as this is considered to be more attractive, while on the other hand taller men have more reproductive succes. The result is an endless feedback loop of height variation across the generations. Neither sex ever reaches its full height potential, a proces also known as intralocus sexual conflict.

If a woman is shorter than average she’ll be more likely to have children. If she has a daughter and a son, they’re likely to be short, thanks to their mother’s genes. This favours the daughter as evolution is pushing her towards her ideal shorter height to pass on her genes. At the same time her son is less likely to reproduce. Since this pattern happens over an entire population, the population as a whole gets shorter because of short women reproducing more. Everyone is moving away from the greater height for men. So far so good, but… that increases the evolutionary pressure for men, so that taller guys within this population reproduce more than their shorter peers, pushing the heights of the next generation back into the average range. “Because selection in this generation is then likely to be stronger on average-height men, the next generation will again be slightly taller,” researcher Gert Stulp said. “This is, of course, to the detriment of women, so that the selection pressure on female height will get stronger to push it back to shorter height again.”

Generally, women embody the physical manifestation of a smaller human species and a desire for tall, while men embody the physical reality of tallness while desiring the small. In the long term, intralocus sexual conflict is resolved when genetic mechanisms evolve that decouple the between-sex genetic correlations between traits. This can be achieved, for example, via the evolution of sex-biased or sex-limited genes. Can we align female physical reality and male desire to inspire a permanently shorter human species?