Simanaitis Says

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WE’RE THE HIGH-ENERGY APES

“WE MAY NOT be raring to go on a Monday morning, but humans are the Energizer Bunnies of the primate world.” This wonderful opening line by Ann Gibbons in AAAS Science magazine encouraged me to read the rest of her article, “Why Humans Are the High-Energy Apes,” in Science, May 9, 2016. Here are several tidbits of the research.

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At its core is a study of primate metabolism, of how humans and other primates transform nutrition into energy. There are two measurements of interest: Basal Metabolic Rate and Total Energy Expenditure. BMR is the energy expenditure of keeping vital functions operating at rest. As its name indicates, TEE accounts for more than rest.

It was long thought metabolic rates among primates were more or less the same, despite human brains being at least three times larger, proportionate to body mass, and thus requiring three times the energy to operate. Also, human reproductive output and slow childhood growth lead to increased energy expenditure of our species.

Possible reasons for human energy efficiency includes a higher quality of food and also its cooking, which lessens the energy spent in digestion.

This new research is something of a Unified Field Theory of BMR and TEE: Compared with our ape relatives, humans burn considerably more calories per day, even when accounting for size and levels of activity. That is, human metabolism has evolved to support our greater brain size and other human characteristics.

Herman Pontzer is a biological anthropologist at Hunter College in New York City. Stephen Ross is a primatologist at Chicago’s Lincoln Park Zoo. Sixteen other colleagues from Ghana, Jamaica, Seychelles, South Africa, Switzerland and the U.S participated in the research. Their study involved apes from 14 zoos and sanctuaries in the U.S. and Africa. The humans studied, 141 adults, came from five different populations around the world. To balance rates of activity, the study matched relatively sedentary humans with captive apes.

Calories burned were analyzed by what Pontzer calls the “gold standard” for metabolic studies: The diet of test subjects included water identified with certain isotopes of hydrogen and oxygen. Then resulting isotope levels were measured in the subjects’ urine. The ratio of ingestion/elimination gave an indication of how much carbon dioxide was generated, which in turn reflected how many calories had been burned by each test subject, human or otherwise.

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Chimps are lean compared with humans, yet the research showed that these apes burn calories more slowly than we do. Image from Science, May 6, 2016.

Together with the 141 Homo sapien subjects, the study included 27 chimpanzees and 8 bonobos, collectively, the Pan genus; 10 of the Gorilla genus; and 11 orangutans, the Pongo genus. After taking body mass into account, the researchers found that humans expended about 400 more calories per day than Pans, 635 calories more than Gorillas and 820 more than Pongos.

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A summary of “Metabolic Acceleration and the Evolution of Human Brain Size and Life History” by Pontzer et al in Nature, May 4, 2016. The dark red is BMR; red completes the total TEE. FFM is Fat-Free Mass. No BMR data are available for gorillas. An abstract is available online.

The researchers also found that humans had significantly more body fat than the other test subjects, even those in zoos as opposed to open sanctuaries. Noted Pontzer, “If you’re going to burn fuel faster, you better have a backup tank.”

It’s also curious that no BMR data were available for gorillas. ds

© Dennis Simanaitis, SimanaitisSays.com, 2016

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