Animals’ instincts to exploit gluts of food to avoid costing searching means we easily become obese in our ‘constant glut’ modern world

Background

Evolutionary explanations for why people become obese tend to focus on fat storage as preparation for a famine that in the modern world never arrives. But if we are really evolved to store an excessive amount of fat then we shouldn’t suffer health costs from storing it. Prehistoric humans didn’t either face famine or barely enough food; sometimes there is a glut of food, such as when trees produce fruit. The modern world can be thought of as ‘constant-glut’ because there is always an excess. We should consider how we might have evolved to respond to a glut.

Findings

We predicted the amount of fat to put on in a short-lived glut that maximizes the long-term survival of an animal that could die of starvation (in a famine), from obesity-related illness, or predation (when foraging), The best amount of fat is that which results in high long term mortality from obesity-related illness, because the gluts in the natural world do not last but the fat can be used up while the animal can avoid having to look for food, which exposes it to predators. People therefore defend an excessive body weight because it was adaptive when gluts were rare and short, and looking for food was risky.

Implications

We predicted the amount of fat to put on in a short-lived glut that maximizes the long-term survival of an animal that could die of starvation (in a famine), from obesity-related illness, or predation (when foraging), The best amount of fat is that which results in high long term mortality from obesity-related illness, because the gluts in the natural world do not last but the fat can be used up while the animal can avoid having to look for food, which exposes it to predators. People therefore defend an excessive body weight because it was adaptive when gluts were rare and short, and looking for food was risky.

Subject

Evolutionary medicine


Subject Group

Zoology and Ecology


Keywords

predation

constant glut

obesity

starvation

optimal foraging


Posted by

AndrewDHigginson

on Fri Oct 27 2017


Article ID

PKYZRN52Y


Details of original research article:

McNamara JM, Higginson AD, Houston AI. Costs of foraging predispose animals to obesity-related mortality when food is constantly abundant. PLoS One. 2015;0141811.

Preceded by:

Great tits distinguish between foods of different quality depending on the frequency of the better type but not on the frequency of the worse type.

Posted by: AndrewDHigginson Posted Wed Dec 20 2017

Understanding how large and how fat different species are follows from predicting optimal bodies that avoid both starving and predation

Posted by: AndrewDHigginson Posted Wed Oct 11 2017


Followed by:

The drifty genotype hypothesis of obesity is not consistent with evolutionary theory

Posted by: AndrewDHigginson Posted Fri Oct 27 2017


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