We all look alike

Humans do show some height variation among population, here a European with Pygmies at the beginning of the last Century. Scan of Collier's New Encyclopedia, Volume 1 (1921). Courtesy of Wikimedia Commons.

We might think that whereas most animals in the same species looks alike, we, humans, show a lot of individual variation. However, new research shows that in fact humans are much similar than we think. The scientists compared variation in length (height) and body mass in various human populations and compared it to animal populations. Surprisingly, they found that humans show some of the lowest levels of variation in height, whereas variation in body was around the average variation found in animals.

If you take a stroll down high street on a busy weekend, you will undoubtedly encounter people of all form and shapes. Some are short, some tall and some are think while others are overweight. However, if you look at cows in a field or butterflies visiting a flower you might not see the same variation. But is this just because humans differ more than other animals or because we pay more attention to differences in our own species.

The two Canadian biologists, Ann McKellar from Queen’s University and Andrew Hendry from McGill University have addressed this question in a new study published in PLoS One.  They searched the scientific literature for data on variations in body sizes (body length and body mass) within and among 99 human populations and compared these to 210 species of animals including invertebrates, fish, amphibians, reptiles, birds and mammals.

The study shows that although variation in body mass in human is within the normal range, then variation in height, especially within a population, is very low. The scientists give two possible explanations for this low variation in height within a population. First, sexual selection could reduce variation as other studies show that taller men often have more sexual partners and get more children than shorter, thus height would be selected for until constrained by nutrition intake and quality. Second, our ability to manipulate the environment could reduce the natural selection on height.

Reference
McKellar AE, Hendry AP (2009) How Humans Differ from Other Animals in Their Levels of Morphological Variation. PLoS ONE 4(9): e6876. doi:10.1371/journal.pone.0006876

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