Humans 'Too' Consistent in Size

In most animal species in the world, the differences between members can be quite significant, which is to say that they lack consistency. However, in humans, that is not the case. Of course, exceptions to the rule exist, but, on average, we have the same general size, a fact that scientists have not yet been able to explain. When comparing ourselves to other species, we vary much less in shape and size than they do, experts say, quoted by Wired.

McGill University evolutionary biologist Andrew Hendry shares that, “We don’t have an answer. We have this interesting observation, but the explanation is an open hypothesis.” Together with Queens University biologist Ann McKellar, Hendry browsed through available data on body shape and size for more than 200 species, ranging from insects to mammals, and from fish to humans. The results of their investigation only deepened the mystery of these variations.

They noticed that, while certain human population groups indeed presented noticeable differences in body size and shape between them, variations within the same populations were, in fact, fewer than in 95 percent of the studied species. For instance, they say, the aborigines of Australia are smaller than Maasai men, but within each groups' villagers, variations were almost negligible. Hendry says that, over millions of years of evolution, humans have adapted to certain environments by reaching certain sizes, and that these sizes were then maintained, with little to no variations, especially within neighboring population groups.

According to the paper, published in this Tuesday's issue of the open-access scientific journal PLoS ONE, the study focused more on studying populations that had a history of relative seclusion, and that were descendants of people that were historically tied to a certain region. One of the proposed explanations for the conformity was that mating rituals were responsible. Males that varied considerably in shape and size may have had unequal chances of passing on their genes, so evolution stepped in to even the odds. However, that is just a hypothesis, the experts point out.

“You had these differences in, say, the Arctic and the Kalahari, with strong selection for body size in those spaces. But now those selective pressures have been removed. We have heating and air conditioning. It’s possible that with time, humans will come to look like other animals,” Hendry adds.