Good reason exists to doubt whether genes advantage black Americans at
             sport as Jon Entine claims -- the phenomena of the birthday or age cut-off
             effect. There is nothing genetic about being born in August rather than
             September but it can profoundly change the odds on becoming a professional footballer or tennis player [as well as being treated for mental
             sub normality or dyslexia]. The cut-off effect shows that big population
             differences need not be genetic since they can arise from apparently small
             environmental ones. The mere existence of different numbers of blacks and
             white in a sport thus says nothing by itself about genetic advantage [that
             requires evidence of correlations between differences at the individual
             level between anatomy and physiological sport related traits and actual
             sporting success] -- dramatic population differences could equally be due
             to apparently insignificant environment factors such as date of birth.
             For example, in the English FA premier league over twice as many players,
             285 are born in the three months Sept-Nov as the earlier three Jun-Aug,
             136. Gene wise they are the same. In a similar way, the Dutch tennis year
             starts from the beginning of the calendar year: half its young league
             players between 12 and 16 are born in the three months January to March
             (Dudlink, 1994; Edwards, 1994). The same effect with different months
             (month cut-offs vary with sports) has been found in cricket with fast
             bowlers, tennis players and hockey players. If having a birthday in the
             wrong month can have such dramatic effects, what might be the effect of
             having a dark skin and the constant prejudice that means you are
             academically born dumb but bodily athletic?
             Such effects could be large due to similar mechanisms to those that create
             the birthday effect. This arises due to a self-amplifying advantage or
             disadvantage in the opportunity to learn a skill. Individuals in a gro...