Are Humans Still Evolving?

Contributed By Kevin Childress, Ricardo Acevedo, and Crystal Seales

Can we be at the mercy of evolution?

A common misconception about evolution is that humans are no longer evolving. It’s very easy to think that because we seem to be the masters of the world around us, there is no need for the human species to be changing anymore. However, if we just look at some examples, we can see that humans are indeed not immune to the power of natural selection. For example, only certain human populations, mainly from pastoral/cow farming heritage, have the ability to digest milk at older ages. If you contrast those humans with humans from East Asia, you see that a large majority from East Asia cannot digest milk due to the lack of dairy in their ancestor’s diets. (For more information, see a recent post on lactase).

But let’s take a look at a more “drastic” example, the pygmy humans. They represent a population of humans around the world that have an unusually small body size that is well proportioned. They are found in certain African, Southeast Asian and South American populations, so they aren’t just an isolated group of people. The groups found in Central Africa are known to be the shortest humans on Earth! These pygmy populations tend to grow at a slower rate than other humans, and they normally stop growing at just 13 years old!

So why are they short? Well, genetic testing has shown that these groups evolved separately from one another. Currently, many hypotheses are being investigated. The most recent one is that this is an adaptation that allows the pygmies to stop growing at an earlier age, and thus reproduce at a younger age. This is plausible because less resources are put into their growth, allowing for more energy to be available to reproduce at an earlier age.  Understandably, however, the hypothesis is highly debated. Others believe that earlier reproduction times and a smaller body size evolved to compensate for a lack of  food and resources in their environment. A shorter stature could also help the pygmies navigate their surroundings and regulate their body temperatures more efficiently.

These hypotheses are an attempt by researchers to explain why the pygmy populations differ physically from the rest of the human species. Even though evidence doesn’t support a specific hypothesis at this time, the current data illustrates that evolution is a force that will continue to influence our species.

Check out our video on the topic!

For more info, see :

Migliano, A. B., Romero, I. G., Metspalu, M., Leavesley, M., Pagani, L., Antao, T., & T Kivisild. 2013. Evolution of the Pygmy Phenotype: Evidence of Positive Selection from Genome-wide Scans in African, Asian, and Melanesian Pygmies. Human Biology 85, 251–284.
Becker, N. S.A., Verdu, P., Froment, A., Le Bomin, S., Pagezy, H., Bahuchet, S. & E Heyer. 2011. Indirect evidence for the genetic determination of short stature in African Pygmies. Am. J. Phys. Anthropol. 145: 390–401.

Simmons, R.E., & L. Scheepers. 1996. Winning by a Neck: Sexual selection in the evolution of giraffe. The American Naturalist. 148: 771-786.

Migliano, A.B., L. Vinicius, & M.M. Lahr. 2007.  Life history trade-offs explain the evolution of human pygmies. Proceedings of the National Academy of Sciences of the United States of America 104.51: 20216–20219.

Meazza, C., Pagani, S., & M. Bozzola. 2011. The pigmy short stature enigma. Pediatric Endocrinology Reviews. 8: 394-399.