Expert: Dana Krempels, Ph.D. - 4/18/2008

Question
it is said that majority of europeans are indo-europeans based on languages they speak. question arise as to difference in looks of asian indo-european and european indo-european. even the fairest of north india cant beat the english in complexion or physical traits. similarly the uralic people r strikingly similar to the neighbouring indo-europeans . could u explain all these from biological perspective ?

regards
satya

Answer
Dear Satyanarayan,

The analogy between the evolution of languages and that of physical traits is a fascinating one.  Thing is, one cannot say that the two evolve at the same rate, or in the same "direction."  I'll address only the physical traits here.

Different races of humans are most likely different in superficial appearance because of the phenomenon known as genetic drift.  This results when a relatively small subset of a larger population is isolated from its parent population, and begins reproducing with only the members of that small group.

This is nicely exemplified in island populations such as the Galapagos, where ancestral species came from mainland South America and gave rise to very closely related species that have distinctive appearance different from that of the mainland species.  (For example, the Green Iguana, (Iguana iguana) and the Galapagos Marine Iguanas (Amblyrhynchus spp.) look different, but are descended from a common ancestral stock.)  

Once isolated from the parent population, a Founder population (be they iguanas or humans who have migrated as a small tribal group to a new, remote territory) will not only be subject to different mutations within the group (that are no longer going to be shared with the parent population), but also different natural selection pressures and other things that can amplify the effects of what is, essentially, inbreeding.  At least after a few generations.

You can see such similarities in human families in which inbreeding has been done to retain family fortunes, such as the British Royal family and the Austro-Hungarian Hapsburgs:

http://www.msu.edu/course/lbs/333/fall/hapsburglip.html

Their inbreeding lasted for only a few generations.  But one can easily imagine that if one of those families was marooned on an island an unable to share genes outside the small group, a new race with the distinctive phenotypic (physical) characteristics of the small Founder population would evolve simply due to a lack of gene flow.

The various races we see today are very likely a result of the same type of phenomenon:  small groups migrated to new territories, and were isolated from the larger populations from whence they came.  The traits shown by the members of those small, migratory groups became prevalent in the group as it grew, and as new mutations arose in their descendants, they didn't share them with anyone else.  So the "look" of a particular subgroup of humans evolved.

That separation can dismantle quickly, though.  In only a single mating of people from two distinctive ethnic groups, there is a clear homogenization of the racial characteristics of each parent.  And with more outbreeding, human races would eventually disappear and be replaced with a homogenous human phenotype.  (Did you ever see that episode of South Park with the human from the future?  Like that.)

Hope that helps, and I hope it was clear enough. If not, please write back.

Dana