Is this really a debated subject though? I still don't think we've seen a good example of what a biologically based prejudice would be...
Biological Bases of Prejudice
Heiner Flohr

Our knowledge of the causes of social prejudice is insuflicient; conventional sociological and psychological approaches should be com plemented by a search for biological causes. Evolutionary theory can explain why there is a need for prejudices. The formation of prejudices is supported by some characteristics of our cognitive apparatus. Apart from that, behavioural tendencies such as group orientation and xenophobia, as well as the biologically rooted rejection of outsiders, contribute to the formation of prejudices. Prejudices are hard to fight because of their biological basis, but insight into this element may indicate effective countermeasures.
Its a highly debated Topic. at least i think.