The Evolution of Fat and A Much Misunderstood Fact of Evolution

Posted on January 31, 2009


I put on a few extra pounds over the holidays. That happens when you eat constantly for four weeks, never exercise, and supplement your daily diet with five to ten thousand calories of beer, wine, rum, and other assorted alcohols. It’s inevitable really.

Now that I am exercising again, not stuffing myself, and drinking less, I’ve noticed that the pounds are a lot harder to take off than they are to put on. My initial reaction was, ah gee-whiz, ain’t life a pain, but then it occurred to me that this tendency to hold weight rather than lose it quickly may have been an advantage at any other period in the history of the human species. Even fifty years ago — and certainly a hundred years ago — turning extra calories quickly into fat that could then be stored for times of scarcity may have been advantageous.

This fact made me think of plump, fat, fatter, and obese persons. Today they are generally regarded to be unhealthy and, perhaps, even genetically unfit — after all, all cultural stereotypes indicate that having a few extra pounds reduces your chances of mating. Now, strictly-speaking, in many cases overweight — truly overweight — people are unhealthy, given the conditions in which most of us live. Famine is not likely any time soon and the stress of the extra weight, as is well known, causes all sorts of health risks and complications. And yet there is a temptation to think, well, isn’t it possible that today’s “bad health” is a result of yesterday’s genetic advantage?

Well, it’s certainly possible because it is true that yesterday’s genetic advantage can become today’s genetic disadvantage and vice versa because of a change in circumstances. As the conditions of scarcity change, so will what counts as an advantage and as a disadvantage. So, yes, obesity today may be the result of yesterday’s genetic advantage.

There is, however, another equally plausible explanation for this trait (assuming it is even inheritable). Our bodies, which are ill-adapted to our contemporary lifestyle and diet, may turn the extra calories into fat quickly because it has no other way to cope with the excess and our bodies may have difficulty burning off the fat because our bodies never needed to burn off that much fat in the past. In other words, our bodies simply don’t have the capacity to deal with these calories because we didn’t evolve in the kind of dietary conditions we have today. This may explain why being even moderately overweight can have serious consequences for our health. Maybe, our bodies simply can’t cope with that which they never had to cope with before.

And this leads me to my main point. There is a crucial feature of evolutionary theory which is often misunderstood even by persons who claim an expertise in the field. Evolutionary theory provides only a plausible explanation why a species — the average characteristics of a specific breeding population — is one way rather than another. Evolutionary theory says there is good reason to think a particular breeding population share in common some inheritable trait or set of traits which give it a reproductive advantage in times of scarcity. It does not and cannot predict what that trait or set of traits is, has been, or will be. It says only that the present instances of the species share some trait or traits which give it a reproductive advantage in times of scarcity.

So, when you hear people saying this or that trait of some species exists because it uniquely provided some evolutionary advantage, they are engaged in speculation — however thoughtful — not really justified by the theory of evolution itself. There are just too many variables to control for, even in an incredibly simple species, to predict which trait or set of traits provided the reproductive advantage and, even then, the environment itself changes too often too quickly to know this or that trait was or always will be an advantage.

For example, big brained scientists who like to use their big brains a lot may be tempted to say it is the big brains of homo sapiens which is its unique advantage but those big brains, especially now, look to be the down fall of our species — thanks to global warming and / nuclear annihilation. For all we know, our species is here because our only direct competitors mutated in some disadvantageous way or simply decided not to breed. Even back in the 18th century it was noted that wealthy well educated persons tended to reproduce less than the poor and uneducated. In other words, we may only be here by default and it may only be a matter of time before our seeming advantage reveals itself to be a disadvantage and we wipe ourselves out. Forget the meek, cockroaches will inherit the Earth.

Understanding the point I am making is important if a person wants a full and proper understanding of evolutionary theory, however, it is also important because my point is the best argument against the greatest misapplication of Darwin’s theory — eugenics. There are lots of reason why eugenics is unacceptable but, crucially, it must be said that eugenics can’t possibly achieve what it intends to achieve, even if some acceptable form of the practice could be discovered. No person or person, however bright, can predict with any reasonable chance of success what trait or set of traits will be an advantage over the short or long term. Better to let a million flowers bloom and see which of them survive than to try to guess in advance which flowers will bloom best. After all, that is exactly what nature has being doing since — well, right from the very start.

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