Humans: the SUVs of the animal kingdom

 

Many of us bemoan our capacity to store excess energy as fat. But while our ability to store large amounts of excess energy might be unnecessary and unhealthy nowadays, it was critical for the survival of our ancestors.

You’ve heard the argument before: Ancient humans and the animals that preceded them evolved in an environment where food sources were scarce and unreliable. Thus, natural selection favored the development of a mechanism for the storage of excess energy to be used at a later date when food could not be found.

It’s a very reasonable argument and it’s certainly true on some level. However, the same basic argument should be applicable not only to humans, but also to other primates (chimps, gorillas, orangutans, etc.) with whom we share an evolutionary heritage. But while those other primates do, of course, also have the capacity to store excess energy, it seems that when it comes to body fat, we humans are in a class of our own.

Now, you’re probably thinking ‘Hold on, the fact that humans have more body fat than other primates might not reflect genetic differences in energy storage capacity at all. Maybe humans have more body fat simply because they eat more and exercise less than other primates.’ But the differences in body fat between humans and primates persist even when primates in captivity are compared with humans that are living more evolutionarily-appropriate lifestyles, like hunter-gatherers or subsistence farmers1,2,3.

So why would humans have developed a capacity for energy storage far beyond that of other primates? The results of a study recently published in Nature3 suggest a simple answer: our energy needs are far beyond those of other primates. When researchers measured the total number of calories burned during the course of an average day for humans and several other primates, they found huge differences, even after correcting for differences in body weight.

And the differences in the total number of calories burned between humans and other primates had almost nothing to do with physical activity – even at rest, humans burn between 10% and 25% more calories than other primates of the same size, suggesting that we are using all of the extra energy to fuel our organs and, in particular, our huge brains.

It is, of course, those huge brains that have allowed us to come to dominate the planet as we do today, and these new results suggest that without an accompanying increase in the capacity for energy storage, the development of our huge brains may not have been possible.

It seems that humans are the SUVs of the animal kingdom, with increased body fat to serve as a fuel tank to keep our gas-guzzling brains running smoothly.

So next time you are lamenting your capacity to store excess energy as fat, try telling yourself that it’s a small price to pay for being so smart.

 

1. Pontzer, H., Raichlen, D.A., Wood, B.M., Mabulla, A.Z.P., Racette, S.B., and Marlowe, F.W. (2012). Hunter-Gatherer Energetics and Human Obesity. PLOS ONE 7, e40503.

2. Zihlman, A.L., and Bolter, D.R. (2015). Body composition in Pan paniscus compared with Homo sapiens has implications for changes during human evolution. PNAS 112, 7466–7471.

3. Pontzer, H., Brown, M.H., Raichlen, D.A., Dunsworth, H., Hare, B., Walker, K., Luke, A., Dugas, L.R., Durazo-Arvizu, R., Schoeller, D., et al. (2016). Metabolic acceleration and the evolution of human brain size and life history. Nature advance online publication.