Nope! Genetics took care of that. A species too distantly set apart from it's common ancestor to another species can't have a child together. The DNA isn't close enough and the genes would be all whacked. And the sperm cell and the egg cell couldn't unite because of the differences. Mostly the number of chromosomes in the sex cells(23 for humans), but all sorts of things play a role in that. I remember learning that in science this year. (Yes, I'm so nerdy that I made a point to remember it, too.)
Nope! The lock an' key have to match(in genetics not like 'that'DX) And in the case of bestiality, that just doesn't work. Humans have a haploid 46 chromosomes and a diploid of 23 in sex cells, so they need another sex cell of 23 to make 46, which would equal a new human. Differents species have different number of chromosomes so our gamates(i.e sperm and egg cells) wouldn't match!