This study found that only nine out of 115 genes known to be associated with obesity showed evidence of being under positive selection.
If you can’t fit into your jeans, don’t blame your genes. New evidence published in Cell Metabolism
suggests that fat-storing genes are not evolutionarily advantageous, with nearly all common obesity-related genes lacking properties of traits that evolved because they provide an adaptive advantage.
Dr. John Speakman, biologist at the Chinese Academy of Sciences Institute of Genetics and Developmental Biology in Beijing, China and PhD student Wang Guanlin set out to understand why there is a high genetic contribution to the risk of developing obesity.
"In modern society, we live in what has been called an ‘obesogenic’ environment [or an environment which tends to cause obesity]. Yet in that environment, some people get fat, while others stay slim,” Speakman told Asian Scientist Magazine.
"This doesn’t make sense from an evolutionary point of view because evolution should favour phenotypes that bring advantages, but the consequences of obesity are almost uniformly negative.”
The difference in susceptibility has a large genetic contribution to it. In 1962, American geneticist Dr. James Neel suggested a theory called the ‘thrifty gene’ hypothesis, which posited that obesity was advantageous in the past, with genes that store fat helping humans survive famines. However, in modern society, they lead to obesity, Speakman said.
"Neel’s theory suggests that there will be selection for genes that cause obesity. Positive selection leaves a ‘fingerprint’ in the genome, so we can search for that ‘fingerprint’ to test the idea,” Speakman explained.
"We made such a search, and found that the markers indicating selection were no more prevalent in obesity-related variants than are found in randomly-selected variants across the genome.”
With data gathered from publicly-available databases such as the Hapmap consortium and the 1,000 genomes project, Speakman and Wang found that only nine out of 115 genes known to be associated with obesity showed evidence of being under positive selection. Moreover, of those nine genes, only four showed evidence of selection favoring obesity, while in the other five, selection had favored leanness.
According to Speakman, future plans for the research include verifying the findings for variants that really are linked to differences in body fatness. The gene variants they tested are related to body mass index (BMI), but BMI is not a very accurate measure of obesity, he noted.
"Second, the known variants only explain abut two percent of the variation in obesity, so there are a lot more genes out there to be discovered and tested to see if they have been under positive selection,” he said. (AsianScientist)
Dr. John R. Speakman
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences