Half-Man,Half-Beast

[bigbanana]

From a biological point of view, why is it that humans cannot mate successfully with animals to produce half-man, half-beast type creatures. Is there something in the genes or DNA that prevents this?
I really would like to know the answer to this question. It's been puzzling me for years and believe me, and I'd like to apologise if it comes across as sordid - it's not my intention, honest!.

Thanks all.

[kempie]

http://en.wikipedia.org/wiki/Species#Definitio ns_of_species