Evolutionary Theories of Obesity

Obesity is a growing problem in developed countries all over the world. In the UK alone, nearly 25% of adults (age 16 and over are obese) and it leads to other problems such as diabetes, heart disease and strokes. Humans haven’t always been obese and while we would like to blame the growing obesity crisis on our genes, it would be wrong to do so. Although our genes do play a part in our metabolism and how we store excess fat, the expanding waistlines of the population is mostly due to a changing lifestyle.

Over the last 60 years, many theories have been proposed in order to explain the increase of obese people in the population. The original theory came for a geneticist called James Neel in the US in 1962. His hypothesis is known as the ‘Thrifty Gene Hypothesis’ which suggested that genes that stored fat were more of an advantage as it meant people would be able to survive in times of famine. It is also thought that members of the population with more fat deposits were more likely to bear children.


One of the biggest critics of this theory, John Speakman, the head of the Energetics Research Group at the University of Aberdeen, put together his own hypothesis which contrasts that of Neel’s in 2008 which is known as the ‘Drifty Gene Hypothesis’. His main critisism of the thrifty gene idea is that, if it were true, more people would be obese in today’s society. He suggests that if it was, at some point in our history, advantageous to be fat, more people would have the ‘thrifty gene’. His hypothesis suggests that earlier in human history it was a disadvantage to be fat as humans were being hunted by predators. In modern times, where predators are not an issue, the heavier members of the population are able to survive.

These, although the most commonly known, are not the only theories as to why some humans are obese. Other theories include ‘Genetically Unknown Foods’ developed by Baschetti in Italy in 1998, ‘Aggression Control’ developed by Belsare et al in India in 2010 and ‘Climate Adaptions’ developed by Sellayah et al in the UK in 2011. The genetically unknown foods theory suggests that obesity will occur when the population is introduced to foods that they are not yet adapted to. The aggression control theory is based on the idea that as humans relied less on fighting in order to survive, obesity drifted into the population. The climate adaptions theory, which is the most recent, is based on the idea that different climates led to different genes being favored to preserve body temperature.

There is no widely accepted theory as to why the world is getting fatter as each theory has experienced criticism and disbelief. More research needs to be done to establish the genes that are involved in our weight (there are suspected to be hundreds) and then maybe an overall answer will be known as to why the increase in obese people. Whether we chose to base it on our genes or not, the truth is that there is an obesity epidemic which is endangering the lives of millions around the planet.


Beil, L; (2014) Ancient Genes, Modern Meals. Science News. https://www.sciencenews.org/article/ancient-famine-fighting-genes-cant-explain-obesity

Speakman, J; (2008) Thrifty vs Drifty Gene Theory of Obesity. International Journal of Obesity. page 1611-1617.


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