Bskeptical, me thinks you protest too much

"All humans on the planet differ from each other by about 0.1% of our genetic makeup, or approximately 3 million base pairs out of 3 billion in the human genome. And each differs from every other human by the same amount whether you take two people from the same village, different villages, from different countries, or from different continents."

I don’t think this is true, that “each differs from every other human by the same amount.” Identical twins, for instance, differ considerably less than the human average—by something approaching zero. Parents, children and siblings differ considerably less than the human average. And I would think this kinship effect would spread out into larger groups—even very large groups.

Ethnic groups are identified, in part, by a commonalty of certain inherited and easily observable characteristics. In other words, it is a group selected for having a subset of similarly arranged base pairs. This group will differ less than the human average. The same would be true if you selected people with HDL cholesterol greater than 50, or all of blood type O.

These groups have been pre-selected for having some similar base pair arrangement, If differences in the rest of the base pair arrangements are randomly distributed within the two populations, individuals in the selected population with have average differences less than the non-selected group. It’s like playing with a fixed deck—of course you’ll get more aces (similarities). You put the extra aces (similarities) in there.

It also seems to me that the inherited, easily observed characteristics are important and very useful indicators of many other genetic similarities. Scandinavian susceptibility to MS, Blacks to sickle cell anemia, Pimas to diabetics, Ashkenazi Jews to Tay-Sachs, and on and on. Such ethnic related diseases are very common.

In fine, I suspect the truth is that two people living in the same village, sharing ancestors from only a few generations back, are probably more genetically similar than two people living on different continents and sharing common ancestors from 30,000 years ago. Those genetic similarities give rise to similar outward appearance, a subset of similar disease risks, and other similar genetically determined phenomena.

But, really, it’s OK for people to be different. It makes the world more fun.

Bob