Most of us don't think very intently about biology. Physics, sure -- we are constantly and often consciously applying Newton's laws whether we're tossing something in the wastebasket or driving down the highway -- but biology? No. Perhaps this is because Darwinian evolution, the central unifying principle of biology, is so poorly misunderstood by the public (thanks in part to creationists who go out of their way to Teach The Controversy in the form of their own tortured misconceptions), or perhaps it is because we fall into the trap of thinking that it's irrelevant to our daily lives, but in any case, it's unfortunate, because we are biological creatures and just about everything about us is informed by our evolutionary origins.
In this post, I want to show how an understanding of the broad principles of evolution and ecology can help us avoid being taken in by a particular silly health fad, in the hope that the reader might learn to apply a similar critical informed approach to other fads as they appear.
So let's consider a fairly common and plausible sounding claim here, one that underlies not just the Paleo Diet but a lot of basic "common-sense" thinking about health and food. The idea is that it's better to have foods that more closely resemble the kind of food we must have eaten in our pre-industrial past, natural raw unprocessed foods, because these are the sorts of foods we evolved to eat. Our bodies simply aren't equipped, so the argument goes, to deal with the incredibly rich diet our industrial age allows us, and all those artificial flavourings and preservatives can't possibly be good for us.
That sounds eminently reasonable, and indeed it does seem to make solid evolutionary sense. After all, if we hominids have had millions of years to refine our ability to produce just the right enzymes to digest fresh fruit and insect grubs, why mess with a good thing? Why on earth would we expect to be able to digest a chemical invented within our lifetimes?
Well, it's reasonable as far as it goes, but it's also incomplete. What it overlooks is that evolution doesn't just explain how we got here; it's the single unifying principle to all of biology, and also explains how every other living thing got here, including the ones that we eat.
See, being eaten is usually how you lose the game of evolution. Every living thing on this planet is descended from an unbroken line of organisms that somehow managed to avoid being consumed until they produced at least one descendant. Every single cell in every body traces itself back through such a line to one common ancestor. Countless siblings have died without issue (often eaten by some other creature), but even they were descendants of unbroken lines of successful ancestors.
This has been going on for something like three billion years. The occasional link in that chain might have survived just by sheer dumb luck, but the law of averages is against luck when such enormous time scales are involved. Most of your ancestors survived because they had an edge over the things that were trying to eat them, or the things they were trying to eat. Not a big edge, mind you. Just enough of one to survive, just long enough to produce offspring.
Evolution isn't about perfection, after all. It's all about just good enough, but after three billion years of it, just good enough is pretty amazingly good, which is why we (and all living things) seem to be so exquisitely well-adapted to our environments.
But we're not. The gazelle is just barely fast enough to escape the cheetah most of the time, and the cheetah is just barely fast enough to catch enough gazelles to make baby cheetahs. Plants (including the ones we eat) have evolved toxins or thorns or other defenses just barely good enough to kill or deter things from eating them enough for some of them to produce baby plants. And we became just barely good enough to survive eating those toxins long enough to produce human babies.
The point here is that the foods we ate in our ancestral evolutionary environment really, really didn't want to be eaten, and they were trying to kill us, and they often succeeded. We just happen to be really tough, and really clever at figuring out ways to get around their defences so we could eat them without being fatally poisoned or otherwise killed. We discovered that if you heat some things over a fire, they become easier to chew and digest. We discovered that if you plant seeds from mutant not-so-poisonous fruit, you get more mutant not-so-poisonous fruit. We learned out to breed plants and animals that were easy to eat, and make more of them.
While Nature is not exclusively red in tooth and claw, and there are lots of examples of symbiosis and cooperation (like tasty edible fruit to get animals to plant seeds in fresh manure), there really never was an ideal time when we lived in perfect harmony with Nature and it gave us everything we needed to live long happy lives. Modern agriculture and processed foods are not some perversion of what once was good and pure; they are a continuation of what we have always done, which is trying to make sure we have enough food to make babies.
I am not saying here that all diets are equally healthy, or that natural foods are bad for you. Some foods are certainly much better for you than others, and there are definitely good reasons to pay attention to what we eat. I'm not a nutritionist or a biologist, and I don't pretend to offer any specific advice as to what you should or shouldn't include in your diet. What I am saying is that just as a solid grasp of the concepts of force and momentum can help you to make better driving decisions, a clear understanding of our evolution and ecology can better equip you to evaluate claims about diet and health.