In my last two posts, I argued against two widespread truisms:
1. The human genome is 99.9% the same in all people.
2. If we look at the 0.1% that does vary, 85% of this variation exists only between individuals and not between populations.
Both truisms are at best superficially true. They don’t mean what many seem to think they mean. Moreover, they’ve been known to be misleading for some time; in the case of truism #1, from the moment it was first presented.
So Mr. Smarty Pants, how much do genes really differ within our species? And how much of this difference clusters into recognizable populations?
I don’t know. The problem is not simply lack of information. We’re dealing with a conceptual, even existential, problem. Genes differ in any number of ways—not only in the timing and magnitude of a particular trait, but also in countless qualitative aspects. If genes vary along a multitude of dimensions, how can we compress this multidimensional reality into one yardstick called “human difference”?
Let’s assume, as I suspect, that 10-15% of the human genome exhibits some variability. Can we say that humans differ by 10-15% from each other? I’m not so sure. For one thing, a lot of this variability is confined to remote, isolated populations that are close to extinction. Their variability is irrelevant to the overwhelming majority of humans.
For another thing, much of this variability has little or no selective value. How relevant are blood types to your daily existence? What about dormant DNA that might reactivate in one of your descendants?
Well, let’s stick to the 7% of the human genome that clearly varies because it has been selected differently in different environments (Hawks et al., 2007). How relevant are those selection pressures now? What’s the point of having a beard if you shave it off every day? And how important are hair and eye color? At one time, these color traits were under intense selection. Do they matter to us today? I suspect most people would say ‘no’ if asked. They would probably affirm that only ‘inner qualities’ matter, i.e., the soul, personality, intelligence, etc. Yet this viewpoint might change once they’re in a drugstore, especially the hair products section or the magazine counter …
Well, let’s stick to inner qualities. How do we weigh their relative importance? For instance, about 30 per cent of people have a gene variant that results in fewer dopamine receptors and, apparently, in stubborn behavior (Hall, 2008). How useful is this quality? For someone like Winston Churchill, it could have made the difference between losing and winning the war. For many elderly people, it might lead them to refuse ‘newfangled’ medication.
It’s hard to compare things that vary in value not only from one person to another but also from one situation to another. Ultimately, the single yardstick is survival and reproduction: does this trait help its bearer to survive and have children? If this is to be our yardstick, we must conclude that some people are ‘superior’ even though their behavior is widely deemed to be inferior, if not pathological. As anthropologist Henry Harpending points out:
Evolution is a double-edged sword. What evolution cares about is that I have more offspring. If you can do it by charming and manipulating, and I'm a hardworking farmer that's going to feed the kids ten years down the road, then you're going to win. Hit-and-run, irresponsible males are reproducing more. That isn't good for anyone except those males, but that's evolution. (Keim, 2007).
Hall, A. 2008. Why the British bulldog spirit is in the genes. Daily Mail, January 10.
Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) early view.
Keim, B. 2007. Humans Evolving More Rapidly Than Ever, Say Scientists. Wired Science, December 10, 2007.