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Wednesday, March 16, 2011

Evolution of Waifs and the Bootylicious


My last Blog post was about hand bags and the reassurance that tastes in accessories have stayed remarkably similar over the last five millennia. A neolithic Trinny and her fellow tribal fashionistas would luck on very agreeable communal gathering in modern retail outlets – setting aside their necessity to pay in pelts and pots.

So what about the women themselves – have they stayed true to form?

If we look back further through prehistory to the palaeolithic era and pure hunter-gatherer societies, there are surviving figurines – like the Venus of Willendorf statuette - that glorify over-indulged and over-endowed women. Does this mean that such women were common or that they were simply more highly valued?

It seems hard to believe that many of the women in hunter-gatherer bands had consistently high access to surplus food, or prolonged absences from strenuous exercise, or the longevity to get fat. I imagine them to be more like Melissa Moon (pictured above) than Oprah.

For non-Kiwi readers Melissa is a New Zealand athlete who won the 33rd Empire State Building Run-Up in 2010, racing up 86 flights — 1,576 steps — to the outdoor observation deck of the landmark New York skyscraper. I am sure that the more curvaceous Oprah Winfrey requires less introduction.

The conventional wisdom has been that – steatopygiac voodoo dolls aside – ancient hunter-gatherer females were like those of contemporary similar societies like the Khoisan of Botswana and the Semang and Sakai of Malaysia. That is that they were small and thin.

Likely, they are typified by the Baka of Cameroon, for example, where few are over 5 feet tall and weigh more than 100 pounds, giving them an average BMI of under 20.


Jeremy Laurance explores the evolution of amplitude in his article ‘In search of the leanest genes’ (UK Independent of 15 March 2011) and in this we can pick up on the insights of current researchers including Professor O’Rahilly of Addenbrooke’s Hospital, Cambridge:

‘The key question, he says, is not why so many people are fat, but why some remain lean. Most lean people are naturally lean. They do not have to struggle to be that way. That points to a genetic explanation – they naturally have smaller appetites or burn off calories more readily and thus can eat freely without thinking.

“We know for sure that a propensity for obesity or a propensity for leanness is rooted in the genes. Some 70 per cent of the variation between people in terms of their amount of body fat is explained by inherited differences built into our genetic make-up,” he says.

“What our work has shown is that a lot of these genes influence how hungry we get and how satisfied by a particular amount of food we are – rather than how fast or slowly we burn calories.”

‘There are about 32 common genetic variants so far identified that influence whether an individual will be fat or lean. Separately, they have small effects, but when taken together with other genetic factors, the overall effect is large. Some people are born lean.

'How, then, can the obesity explosion in the past 50 years be explained? It is too short a period to be accounted for by genetic selection, which takes place over thousands, or millions, of years.

‘In the 1960s, the American geneticist James Neel developed what became known as the “thrifty gene” theory to explain the increase in obesity. According to his hypothesis, the “thrifty” genotype would have been advantageous for early humans, allowing them to store fat in times of abundance and survive in times of food scarcity.

‘It was thus preferentially selected through millions of years of evolution. But what used to be an advantage – the ability to store fat – has become a disadvantage in modern societies with an abundance of food. This genotype prepares individuals for a famine that never comes.

‘The result is obesity. The “thrifty gene” argument begs the question: why isn’t everyone fat?

If everyone has it, everyone should have the same tendency to put on weight in the presence of an abundance of readily available food.

“One theory is that we do all have it – and it is just our lack of moral fibre and the willpower to control our appetite that makes many of us fat. That doesn’t seem right to me – perhaps because I am chunky myself,” says Professor O’Rahilly.

“The biologist John Speakman from the University of Aberdeen has re-examined the ‘thrifty gene’ theory and suggested that it doesn’t necessarily add up.

“He has suggested that famines weren’t a huge threat before the advent of farming and could not have had sufficient differential impact on survival of the lean and obese as to have had such a powerful selective effect.”

Speakman’s alternative theory – the “drifty gene” hypothesis – is that the modern distribution of obesity stems from a genetic drift in the genes that control the upper limit on our body fatness.

Until about two million years ago, it was important for humans to remain lean in order to have the best chance of escape from predators. But once they started living in groups and discovered fire, they became less vulnerable. So being fat mattered less.

Random mutations in genes that caused weight to drift upwards would then not have been selected against. “It is like having a thermostat in the brain that controls where on the fat spectrum you are going to be,” he explains. “Some would stay the same, some would drift down, but quite a few would drift up.

“The explanation for the modern obesity explosion is that only in the last 50years have humans had enough calories available without expending vast amounts of energy to get them. Obesity used to be a disorder of the rich –now, it affects everybody.

The “drifty gene” theory provides a more satisfying explanation of why a large proportion of the population remains lean. We have all drifted naturally to our set level of obesity. Lean people are mostly naturally lean.”

Genes can still dictate 70 per cent of the variation, even as average weight rises as a result of modern environmental influences. Professor O’Rahilly insists he is not nihilistic about the future. Controlling obesity will, he says, require sustained pressure on the environmental side but may also require intervention on the biological side.

“We study the genetics to understand the wiring under the car bonnet. If we can understand it, maybe we can tweak it.”


I am reasonably happy with the ‘drifty gene’ hypothesis but it does beg some questions. Why, for example, do some hunter-gatherer societies, like the Khoisan of southern Africa contain a significant proportion of women with abnormally large buttocks (steatopygia), and why are the Pacific Islanders as a group marked by both their athleticism in early life and the frequent onset of obesity in later life.

The answer must surely lie in the desirability for societies to contain a mixture of lighter-bodied athletes and fat-storing famine survivors – with the mixes of individuals and genes being decided by natural selection and sexual preference.

This has been suggested as the explanation for widespread obesity in Pacific Island communities with the accompanying medical burdens of high blood pressure and diabetes. The story here goes that the original Islanders were of similar build to their distant cousins the indigenous peoples of Taiwan and the Philippines – fairly slight and short.

But, it is argued, long Pacific voyages favoured those who stored fat most effectively – reserves that could be drawn on as voyages lengthened and landfalls became more chancy. And it seems that there is certainly no sexual discrimination against the large of frame among these societies – in fact probably the reverse.

This is the genetic inheritance of some magnificent Rugby players and shot-putters. But the trait also explains the background to those large ladies who attend Samoan churches in white hats - and the overweight girls who frequent the KFC outlet in the Wellington suburb of Kilbirnie.

Getting back to steatopygia, I was saddened to read about the exploitation of "Saartjie" (Little Sarah) Baartman who was put on show in Europe in the last five years of her life (1810-1815), following her previous enslavement in the Cape Colony, South Africa. Sarah was a Khoisan and she was touted by her show masters as the ‘Hottentot Venus’.

Although I was generally appalled by her treatment during her exhibition in Britain and France, I was touched that she was baptized in Manchester Cathedral in 1811 – the venue that was the scene of the marking of many a hatching, matching and dispatching of the members of my own Shorrocks family from Salford.

The other twist here though is that the Khoisan are being increasingly recognized as the best modern representatives of the ancient lineage of modern man. So if you see a lady with an ample derriere – a feature which is currently undergoing something of a revival with the popularity of bootylicious singers such as Jennifer Lopez and Beyonce – you can celebrate something that sticks out and goes right back.

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