Since environment and genetics play an interwoven game in the development of human traits, there may occur genetic changes over time. Darwin interfered with an Austrian geneticist in his finding just that, accusing him of faking some result to coincide with its implications. The Austrian guy killed himself on account of this incident.
In effect , if genetic changes can occur on account of environmental alterations, then the desired traits may be enhanced, or depreciated on that account.
For instances, looked at it memetically, let’s say that the desired trait is physical beauty and attractiveness.
The unhappy man, is not attractive to a beautiful blond gold-digger, since he is poor. Nth environment reduces his chances of gaining that trait, therefore
that trait will eventually be extinguished, for the next generation of the man will not be beautiful.
Since the offspring of this poor man will not exhibit the traits of beauty, they will have to compete more furiously in the genetic marketplace, and the way the ‘compensation’ occurs, is that more brains will be developed, to be able to overcome the lack of beauty and attractiveness. Then beauty will be subordinated in future generations to brain, and slowly intelligence will become the primary desirable trait. Hence, more and more differentiation of racial characteristics will develop, due to circumstantial changes.
Politically expedient solutions, will diminish the chance of racial purification, the farther history is moving it into the future from the age of monarchy.
Extreme purity had it’s apex when the aristocracy practiced intermarriage in between familial lines. The results were disastrous , as history can attest to it.
The problem here, is boundaries, how close, yet how far could margins be established, where desired types may be practically established, without causing aberration on one hand, or the acquisition of undesired traits on the other.
I think environmental manipulation, or simply the developing process of social change, can and does find it’s level, whether it be caused by consciously desired traits, or not. Past generational genetic aspirations can also play a key role in feeding unconscious motives in establishing some kind of stasis of genetic/environmental balance in individual humans.