in regards to the original post, i think that while there is some merit to the idea that some additional natural selection was applied to slaves going to america, in the form of hard physical labour, poor conditions, and the bias of the slavetrader/owners, i think that the theory falls on its arse because it doesnt take into account various cultural forces that manifest in the overall caractreistics of any race/social group
now first and foremost, i would question the idea that blacks dominate in sport. sure, there are some high profile black sprinters, basketball players etc etc etc, but i would like to see some statistics before asserting that they 'dominate' in sport. i think it is fair to say that many successful black athletes are very marketable, and perhaps over-represent their demographic, or, going back to the cultural aspects touched on earlier, that american culture, at present, currently values sports that black athletes excel in very highly, thereby furthering the over-representation of black athletecism.
you could focus on other angles as well - socioeconomics being important. to generalise (just to make a point, everyone get a grain of salt out please), wealthier parents generally push their children into study more than athletics, effectively hamstringing their children from an athletic viewpoint by diverting their time/interest. we could (if we wanted to) assert that black people a generation ago (whose children are only now coming to athletic fruition) were more likely to fall within a poorer socioeconomic class and thereby have this athletic advantage. then, coupled with americas taste in the sports in which these athletes are likely to excel, we have a situation in which our present "black sports domination" stereotype can come to light.
something that noone has yet said is that, at the end of the day, slavery has existed for millenia. take a look at the turks, who for a period easily equivalent to that spanning black american slavery, would take the strongest male children from a number of races (greeks/macedons/romanians/some germaic races) to form the core of their fighting force (known as the janissaries). surely the natural selection imposed on this group of people, in the form of byzantine warfare and hand to hand combat, would have exerted teh same (or greater) selective pressure as the (mere) field work done by black slaves - and, despite this period of slavery ending only 200 or so years ago, we have not seen a turkish parallel to the current "black sports domination" spoken about in this thread (even though other factors may come in, such as inability or lack of opportunity for these warrior slaves to breed, or that the best of them were killed before they could, or that they did so, but were assimilated and absorbed by the current living turkish population)...or the fact that there was no opportunity for turks (post and present) to show their true mettle, given the lack of an equivalent to american cable tv.
soooooo, i would think that any logical, rational person would say, in regards to the original post, that the idea of black sports domination, IF actually true and not a result of an over representation of black athletes or some silly white inferiority complex giving rise to such perverse thinking, is in fact a multifactorial phenomenon that cannot be simply attributed to the selective pressure constituted by a mere 4 or so centuries of slavery, particularly when viewed in the context of equivalent (or greater) selective pressures experienced by many other peoples throughtout history, that have not resulted in the creation of a 'super race'
besides, we all know that the selective pressure applied to greeks throughout their tumultuous history already resulted in a scarce, yet superbly developed number of humans who may be seen as several cuts above the norm, perhaps to the level of super-humanism, since....i mean....theres me