Ego, the gene, te absolvo

Now there’s a “fat gene.” 16% of the population have two copies of a variant of a gene (of utterly unknown function), which correlates with a 70% increased risk of obesity and an increased risk of type II diabetes. If you have one copy of it (probably well over 30% of the population), you’re slightly heavier on average.

If you believe the news stories, this explains the obesity epidemic! People just can’t help it: their genes make them fat. Well, sorry to burst their bubble, but the distribution of this gene in the population cannot have changed over the time period when obesity has become a huge problem. Genetics just don’t work that way, particularly in cases when a variant is so common. Back when very few people were obese, because food was scarcer and manual labor was more common, almost the same percentage of people carried the “fat gene.”

So, let’s go back in time to the age before the Agricultural Revolution. Malnutrition and starvation were a daily reality for many people. What if you had the “fat gene” then? You would probably store fat better than the skinny among us, so you’d be more likely to survive long periods of time with little or no nourishment. What has become maladaptive today would have been a big advantage in times of scarcity.

There are any number of examples of this phenomenon. Sickle cell anemia is quite common in African and African-American populations; having one copy of the gene is not particularly dangerous, but it does confer resistance to malaria. Cystic fibrosis is fairly common in Caucasian people; one copy of the mutant chloride channel probably leads to resistance to secretory diarrhea. One copy of the “fat gene”, and maybe even two copies, must be adaptive, or otherwise such a large percentage of the population would not have preserved it.

In the end, what is causing obesity today is not your genes, but your diet and lack of exercise. Having the misfortune of living with two copies of this particular genetic variant only makes it more likely that you will have trouble keeping weight off. Diet and exercise just become more important to you than the rest of us. This “thorn in the flesh” does not absolve you of responsibility; it merely complicates things. Almost nothing in life is entirely “nature” over “nurture.” Our modern society seeks anything to avoid the reality of responsibility, but such self-deception helps no one.

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