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Humans have faster metabolism than closely related primates, enabling larger brains

Loyola University Chicago researchers are among the co-authors of a groundbreaking study that found humans have a higher metabolism rate than closely related primates, which enabled humans to evolve larger brains.

Humans have faster metabolism than closely related primates, enabling larger brains
Researchers have found humans have a higher metabolism rate than closely related primates, which enabled humans
to evolve larger brains [Credit: Lincoln Park Zoo]
The study, published in the journal Nature, found that humans also have a higher percentage of body fat, providing the energy reserves to fuel their faster metabolism. The findings may point toward strategies for combating obesity, researchers said.

The study found that, adjusted for body size, on a daily basis humans consume 400 more calories than chimpanzees and bonobos (closely related to chimps), 635 more calories than gorillas and 820 more calories than orangutans.

Co-authors of the study include Amy Luke, PhD, Lara R. Dugas, PhD, and Ramon Durazo-Arvizu, PhD, of the Department of Public Health Sciences of Loyola University Chicago Stritch School of Medicine and Graduate School. First author is Herman Pontzer, PhD, of Hunter College in New York.

The study confirmed the researchers' hypothesis that humans evolved a faster metabolism and larger energy budget to accommodate larger brains, which consume more calories. The higher metabolism also supports having more offspring and a longer lifespan.

In the study, researchers used an objective technique to measure total energy expenditure in humans and great apes. Total energy expenditure includes calories burned by the body's metabolism at rest, plus calories burned during physical activity. (The technique researchers used to measure energy expenditure is called the doubly labelled water method.) Total energy expenditure was measured over seven to 10 days while the apes and humans followed their normal routines. The study included 141 humans and 56 zoo animals: 27 chimpanzees, eight bonobos, 10 gorillas, and 11 orangutans.

The study found that the percentage of body fat was markedly higher in humans, and only humans showed a significant gender difference -- 22.9 percent body fat in men, 41.7 percent body fat in women.

The human data were derived from a separate study, headed by Luke, called the Modeling the Epidemiological Transition Study (METS). Luke and colleagues are seeking to understand the relationship between physical activity and energy expenditure and weight gain in adults. The METS study includes adults from the United States, South Africa, Ghana, Seychelles and Jamaica.

Humans and great apes together form a superfamily called hominoids. Metabolic measurements of hominoids may point to ways to fight obesity and metabolic diseases such as diabetes and heart disease.

"Humans exhibit an evolved predisposition to deposit fat whereas other hominoids remain relatively lean, even in captivity where activity levels are modest," researchers wrote. "Untangling the evolutionary pressures and physiological mechanisms shaping the diversity of metabolic strategies among living hominoids may aid efforts to promote and repair metabolic health for humans in industrialized populations and apes in captivity."

Source: Loyola University Health System [May 04, 2016]

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  1. This paper confirms what is long known: that humans have larger brains than apes, that brains use a lot of energy, that orangs are rel.slow apes, and that humans use more energy than apes, esp. orangs.
    The paper does not tell us why. I guess Pontzer cs assume that human ancestors left the forests (where apes live) for the plains, where they walked bipedally, and that this in some way led to more energy expenditure, larger brains, fatter bodies etc. But other primates that leave the forest for the plain don't get larger brains, don't become bipedal, and don't become fatter, on the contrary, e.g. savanna baboons are less vertical than forest baboons ("baboon paradox").
    The authors forget the only possible biological explanation why humans differ so stronlgy from apes, an explanation that has been known for >50 years, but has been systematically neglected in most of the paleo-anthropological literature: human ancestors (genus Homo) did not directly go from the forest to the plain, but they evolved gradually from living in wetlands & swamp & coastal forests (Pliocene African hominids incl. australopiths, google e.g. bonobo wading) to living in less forested coasts ("coastal dispersal model", e.g. S.Munro 2010), google e.g. econiche Homo.

  2. I forgot to say: our Pleistocene ancestors (archaic Homo) did not run over open plains: that would require too much water & sodium (= sweat) which both are scarce in savannas.
    Instead, they simply followed African & Eursian coasts (incl.islands: Flores, Cete etc.) & rivers, where they beach-combed, dived & waded bipedally for littoral, shallow-aquatic & waterside foods (shellfish are of all human foods richest in brain-specific nutients).
    This coastal dispersal model (S.Munro 2010) most parsimoniously explains not only human higher metabolism vs apes, our fatter bodies & larger brains (carnivores have no larger brains than equally large omnivores), it explains also why we lost our fur, got longer noses but poor olfaction, spread rapidly over the world etc.
    The term "coastal dispersal" is more accurate than "aquatic ape": it's not about apes or australopiths, but about Pleistocene Homo (not about Miocene human ancestors as Alister Hardy & Elaine Morgan thought), and "littoral" or "coastal" is more correct biologically than "aquatic", see my paper: The aquatic ape evolves: common misconception and unproven assumptions about the so-called Aquatic Ape Hypothesis. Hum.Evol.28:237-266, 2013.


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