Did getting fat help us evolve? Our ancestors' ability to put on weight helped develop larger brains

Abigail Beall
Daily Mail
Wed, 04 May 2016 14:42 UTC

© phenomena.nationalgeographic.com

Most people would consider fat an unwanted part of their body.

But without our ability to store such tissue, our ancestors might not have developed such big brains compared to other primates, new research suggests.

The study shows storing fat helped boost our metabolism compared to other primates, which helped us develop our larger brains and ultimately separated us from our chimp cousins.

Professor Herman Pontzer from Hunter College, New York, and colleagues conducted the study by measuring the calorific intake of humans, chimpanzees, bonobos, gorillas and orangutans.

The researcher group consisted of scientists from Ghana, Jamaica, Seychelles, South Africa, Switzerland and the US.

Humans are different from other primates in that they live longer, breed more, have more body fat, relatively smaller guts, and relatively large brains.

And this uses up more energy, according to the researchers.

'We've known for a long time that human brains, and other energetically costly traits, like faster reproduction and longer lifespans, present a real puzzle: how do we fuel them with sufficient energy each day?' Professor Pontzer told MailOnline.

'Up until now, the standard answer has been that we've somehow carved energy savings out of other organ systems or behaviors, but it's been clear for some time that those "trade-off" explanations are insufficient,' he added.

'Our paper shows that humans have evolved a faster metabolism, using more calories per day, and that this larger "energy budget" readily accommodates the extra costs of our larger brain, faster reproduction, longer lifespans, and increased activity levels - the suite of traits that makes us human.'

© Mary H. Brown

Professor Herman Pontzer from Hunter College, New York, and colleagues conducted the study by measuring the calorific intake of humans, chimpanzees, bonobos, gorillas and orangutans. Gorillas are the largest ape, but expend less energy for their size than humans or chimpanzees. An adult male gorilla pictured

The study found that, when adjusted for body size, humans consume 400 more calories than chimpanzees and bonobos, 635 more calories than gorillas and 820 more calories than orangutans on a daily basis.

They also found humans have evolved a faster metabolism and larger energy budget, with total energy expenditure (TEE) greater than all other primates.

The percentage of body fat was markedly higher in humans, and only humans showed a significant gender difference with an average of 22.9 per cent body fat in men and 41.7 per cent body fat in women.

Humans have increased metabolic activity in their organs, so burn more energy than other primates even when doing nothing.

Much of the increase in TEE is because of humans' greater basal metabolic rate, the amount of energy required to keep the body functioning at rest, measured in kilocalories per day.

The researchers concluded the increased body fat developed alongside our faster metabolism because our bodies could cope with increased energy demands, allowing our bigger brains to grow.

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,' the researchers said.

© Mary H. Brown

A mother chimpanzee and young offspring. Chimpanzees expend less energy each day than humans, but more than other apes. Humans have evolved a faster metabolism and larger energy budget, with total energy expenditure (TEE) greater than all other primates.

'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.'

Comment: We became human BECAUSE we ate meat: Kleiber's law and how humans got their big brains

Meat eating made us human. The anthropological evidence strongly supports the idea that the addition of increasingly larger amounts of meat in the diet of our predecessors was essential in the evolution of the large human brain. Our large brains came at the metabolic expense of our guts, which shrank as our brains grew.

In April 1995 an article appeared in the journal Current Anthropology that was an intellectualtour de force and, in my view, an example of a perfect theoretical paper. "The Expensive-Tissue Hypothesis" (ETH) by Leslie Aiello and Peter Wheeler demonstrated by a brilliant thought experiment that our species didn't evolve to eat meat but evolved because it ate meat.