Thrift at Winspit Quarry

Thrifty, Drifty, and Crafty Paths to More Obesity

Perhaps the most basic question behind this week’s extraordinary meeting at the Royal Society is how did we wind up with so much obesity? John Speakman addressed this on the final day, explaining that the thrifty genotype hypothesis has been popular ever since James Neel proposed it 60 years ago. But it turns out that the thrifty genes concept doesn’t quite fit with the facts and drifty or crafty genes might more fully explain the the path we’ve followed to such high obesity rates.

The Gaps

The idea that evolutionary pressure led people with thrifty genes – genes that promote fat storage – to survive in times of famine makes a lot of intuitive sense. So it became the source of clever catch phrases like survival of the fattest.

However, Speakman tells us that the time course of genetic selection and the frequency of famines means that a thrifty gene promoting obesity would have long ago become a universal fixture in the human genome. Between famines, everyone would get fat. But this is simply not true for hunter gatherers. These populations stay lean, even in times of abundance.

The Drift

As an alternative, Speakman suggests that the genetic basis for obesity is better explained by a “drifty gene” hypothesis. Human physiology protects us from weight loss or weight gain outside of the bounds of a range within which a person’s weight might fluctuate with environmental influences. But individual responses to changes in the environment are a function of random mutations in a person’s genetic code:

“Some people will get fat, some will stay slim, but it just depends on the lottery of what mutations happened in your history. And that’s completely consistent with this absence of any signatures of selection. That basically is the drifty gene hypothesis.”

The Craftiness

In contrast, Jonathan Wells proposes that we consider a crafty genotype hypothesis. The idea is that evolutionary pressures related to adiposity are not all about storing fat simply to survive lean times. Rather, adipose tissue serves many functions in many different contexts that aid in our survival

“Fat is much more than just a petrol tank for an energy store of calories in the body. I would suggest that we should look at body fat as a risk management system.”

As such, says Wells, adipose tissue acts almost like a second brain that manages risks from food, disease, social, and physical environment – risks that our conscious brain functions might not be so good at managing. Thus, he says a crafty or adaptive obesity genotype evolved to help us cope with these stresses – much more than just the acute stress of famine.


So, the genetic mismatch between our modern environment and our gene pool is much more complex than an explanation about storing fat to survive a famine. But the mismatch is undeniable and the better we understand that mismatch, the better we can figure out solutions for preventing and coping with the obesity that results.

Click here for Speakman’s presentation and here for the presentation by Wells. For more on the drifty gene hypothesis, click here, and then here for background on the crafty gene hypothesis.

Thrift at Winspit Quarry, photograph by Ian Andrews, licensed under CC BY-SA 2.0

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October 22, 2022