Throughout our hunter-forager days, humans have developed a subconscious urge to over-eat and became less and less psychologically equipped to avoid obesity, especially during the winter months, a University of Exeter study recently found. Evolving in an environment where food security was only a pipe dream, the lack of an evolutionary mechanism to help us resist the temptation of sweet, fatty and unhealthy food is understandable, researchers state.
People ultimately are animals themselves, and like all animals we’ve evolved and adapted to living in the wild, tailoring our biology to the rigors of an often harsh and unforgiving environment. In the wild, from a survivalistic point of view being overweight brings much to the table for relatively little cost, but being underweight could be life threatening. So we’ve developed an urge to eat in order to maintain body fat; an urge that only gets stronger in the winter, when food became scarce in the natural world.
This, scientists believe, explains why our winter holidays traditionally revolve around bountiful meals and why our New Year’s resolutions to lose all the extra weight fail so utterly. We don’t live in the wild any more though, and we know that being overweight is detrimental to our health in the modern world, so..
Why don’t we put the fork down?
“You would expect evolution to have given us the ability to realise when we have eaten enough, but instead we show little control when faced with artificial food,” said Dr Andrew Higginson, from the College of Life and Environmental Sciences at the University of Exeter, lead author of the study.
Higginson’s team used computer modelling to predict the optimal amount of fat that animals (including humans) should store, assuming evolution has given them physiological and psychological tools to maintain their healthiest weight. Their results show a strong correlation to the availability of food and predatory risks; in other words, when food is scarce animals should attempt to build their fat reserves to have a better chance of surviving if they can’t find anything to eat, and shed the extra pounds when food is readily available to give them a better chance of escaping predators (and looking less tasty.)
Overall, the model shows that there is sort of a tipping point, a target body weight above which the animal should try to lose weight and below which it should attempt to gain fat. But their simulations also showed that usually there’s only a small negative effect on energy stores (i.e. carrying those love-handles around) when exceeding the optimal point; evolution understands this really well, so any subconscious mechanisms working against becoming overweight are a feeble defense to the immediate physical reward of eating tasty food. In modern society where food is really tasty and readily available, the urge to eat becomes much more powerful than our internal weight-o-meters.
“Because modern food today has so much sugar and flavour the urge humans have to eat it is greater than any weak evolutionary mechanism which would tell us not to,” Higginson goes on to say.
“The model also predicts animals should gain weight when food is harder to find. All animals, including humans, should show seasonal effects on the urge to gain weight. Storing fat is an insurance against the risk of failing to find food, which for pre-industrial humans was most likely in winter. This suggests that New Year’s Day is the worst possible time to start a new diet.”
The evolutionary model also shows that there is no evidence to support the “drifty gene” hypothesis, which some researchers have previously suggested would explain why some people become overweight and others do not.
The research, “Fatness and fitness: Exposing the logic of evolutionary explanations for obesity” is published online in the Proceedings of the Royal Society B.