Human Variation: Getting a handle on it.

Human beings are 99.8% genetically identical. Any variation comes from that .2%. Of course, people with different characteristics are going to have a greater genetic variability. In general, Africans will have a different genetic makeup than Europeans within that 15%.

No. Variability is a statistical measurement. It doesn't tell you how much individuals differ from each other, but about how much a population deviates from an average.

I'm oversimplifying a bit, but what this means is that the measure of variability for a racially homoegenous group (whatever that means) is approximately 85% as great as the variability for a racially diverse group.

Another way to look at it: if you take a racially diverse group and compare their DNA, you will observe a certain amount of variability. Of the variability you observe, only 15% can be accounted for by race.

(Again, this is a gross oversimplification, but that's the gist of it.)



The problem is how you identify race -- and it's obviously a loaded term. Most human groups existed in relative isolation for many millennia. When a population is isolated, a phenomenon called genetic drift occurs. Both statistical and living models show us that isolated populations tend to lose genetic diversity.

So, if race really does refer to the geographical origin of a person, it can be quantified to a certain extent.

However, definitions of race generally do not make such fine distinctions. "Black" is pretty meaningless. Does this include both sub-Saharan Africans and Melanesians? On US government quesionnaires (these days), it generally doesn't, but that hasn't necessarily always been the case.

And even if it does include "only" sub-Saharan Africans, it is a still a category that covers a large number of groups that have been effectively isolated from each other throughout most of recent human history.

But if you're going to go ahead and make racial distinctions, what is your standard going to be? You could classify Aborignal Australians as a single group -- but you'd have a hell of a time finding common characteristics. There is no commonality of hair color or curliness, of pigmentation, of facial features. And these are the benchmarks by which race has traditionally been measured. And why is that? Because the individual groups of indigenous Australians have been isolated from each other for far longer then most African, European, Asian, or Native American groups. Groups from western and eastern Australia may well be more genetically distinct than folks from Russia and Malawi. (Or not, I dunno, and don't much care.)

And, finally, a lot of folks have a notion that racial characterics are significant, even when historical differences are eliminated, and that's just a load of crap. All of these differences have come about during a blip in human evolution. The color of an individuals skin, the straightness of their hair, the shape of their eye signifies nothing more. We only find variation in such characteristics because chance variation doesn't kill us. They aren't important characteristics, so they can change when populations become isolated.

I should also mention, as part of my aimless ramble, that while the vast majority of variability in how we are put together occurs in places where it doesn't really matter (i.e., skin color), so too does the vast majority of variability between individuals' DNA come from bits that don't matter: stretches of DNA that do not code for anything, that are just passed from generation to generation without having any effect on anyone.