In a New York Times Op-Ed yesterday, Daniel Lieberman, a professor of human evolutionary biology at Harvard, offers an evolutionary explanation for our obesity epidemic and provides some context for the ongoing debate over limiting or taxing portion sizes of sugary soft drinks and other sweets. The essay is not long and is well worth reading.

According to Lieberman, when humans first split off from their evolutionary cousins, food was scarce and its availability was unreliable. To accommodate circumstances of scarcity, whenever early humans would find food they would gorge themselves, consuming much more than was immediately necessary. Our bodies evolved to convert that excess food to fat which was stored in readiness for the inevitable time of scarcity. Having no food for a time was not fatal because our design allowed the stored fat to be used as energy and keep us alive.

For millions of years, this system maintained a rough equilibrium in humans, with the amount of food consumed balanced by the amount of energy expended. This was partly due to the fact that sugar, which has no nutritional value but is just pure energy that is immediately converted to fat when consumed and not used, was relatively rare and expensive. All of this changed in the 1970s when American scientists found a way to convert corn into a sweetener that was far cheaper and more readily available than sugar. Since then, corn syrup and high-fructose corn syrup have revolutionized the American diet but not in a good way. Soft drinks, candies, baked goods, all manner of sweets became cheaper to produce. The bigger the portion, the higher the price that could be charged while the unit cost to produce increased by only a fraction. For corporate America, corn was not only converted into a sweetener, it was converted into gold because of its huge profitability. Massive amounts of sometimes deceptive advertising (“fat free” cookies are packed with extra sweeteners and have more calories than traditional varieties but who reads the fine print) along with our natural evolutionary impulse to gorge ourselves with as much food as possible whenever possible helped fuel the obesity epidemic.

In concluding his essay, Lieberman writes favorably of governmental restrictions on the advertising and sale of these high sugary products at least as far as kids are concerned since they in particular aren’t old enough to make rational choices about their food intake. When a bad eating habit is ingrained early, it tends to stay with you for life; hence the obesity epidemic.

I tend to agree with Lieberman (and with Mayor Bloomberg) although I think the collateral damage caused by negative public reaction to such proposals devalue the anticipated benefits so much that it might be unwise to take on the battle in the first place. But to all those who cry “nanny state” in response to such proposals, I have two responses. First, as long as we all have to cover the life-time health care costs of all those who end up with serious illnesses caused by obesity, the consequences of an individual eating to excess are a societal concern. Second, one of the reasons corn is such an inexpensive sweetener is that our government has massively subsidized the cultivation of that crop. It seems only fair and balanced that if government action helped cause the problem, government action should help solve it, as well.