February 2, 2011

British Professor Refutes Current Theory on Obesity Genetics

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Prof. John Speakman, biology, University of Aberdeen, spoke about the problem of modern day obesity at the Carrier Ballroom in the Statler Hotel Wednesday evening.

During his lecture, the British professor discussed obesity, diabetes and his recent work that challenges the long-held thrifty gene hypothesis.

According to Speakman, the thrifty gene hypothesis argues that natural selection favors genes that predispose humans to obesity and diabetes because they were advantageous in the ancient world. People carrying these genes were able to survive famine because it allowed them to stock up on food and nutrients more easily during times of abundance.

The hypothesis says that, because famine is not as common in the modern world, the result is wide-spread obesity and related conditions like diabetes.

Speakman argued against this theory,  citing several counter arguments and explaining his own contrary theory. He used historical data from past famines in his first argument.

“Most people who die in famines didn’t die of starvation. Most people don’t die from running out of energy, which would be consistent with the obesity idea,” Speakman said. “The people who die in famines are the young and elderly, not the lean.”

Additionally, if famines have been a threat to humans four to six million years, then natural selection would have caused all modern humans to possess the DNA that make people fat, Speakman said.

He also considered the case that famines only became a threat to humans with the invention of agriculture about 15,000 years ago. He argued that there has not been enough time for the natural selection of thrifty genes to have taken place.

The professor offered a different theory on obesity, “the drifty gene hypothesis,” which is based on his own research. With the invention of weapons and fire, the predation of humans decreased and upper body fitness became less of a vital trait, he said.

Therefore, over time, random gene mutations that increase the human body’s upper limit on fatness were not affected by natural selection, Speakman said. This led to increasing upper body weight in some people, inspiring the name of his theory.

“The key problem to be explained by any evolutionary scenario is why some individuals get obese in western societies but may of us don’t,” Speakman said. “The famine and thrifty gene hypothesis cannot explain this, but the release from predation and random drift in the upper intervention point model provides a possible explanation.”

Speakman is the recipient of the  Zoological Society of London scientific medal in 1995 and the Royal Society of Edinburgh Saltire Society Scottish Science medal in 2003. He is also the author of the book, Doubly Labelled Water.

Original Author: Michelle Honor