Hi CosmicAtheist,
1. Why are all other Homo's in the Genus (except us) extinct?
I don't see any greater significance to the situation that three of four known hominid species have gone extinct in recent geologic history, than they could not survive in their environment. The fourth may be on its way to extinction as well in the same geologic time frame and possibly due to the same environmental influence; that being cultural.
2. As we continue to evolve will there eventually be another speciation event where a group of humans become too genetically incompatible with another? Or since we are so great in number and widespread is this no longer possible?
If humans were not so rapidly changed and influenced by our 'big brains' (Kurt Vonnegut's motif in
Galpagos: A Novel) then I would say yes, there would come about evolutionary change to people. But, because symbolism and language has sprung up among humans, I too see as many others before me, that our genes are operating now within a larger framework of cultural change far more influential upon our future than anything else that genes or selection could cause.
I was just reading the Wiki article on
technological singularity. If you read it I think you might come to the same conclusions as so many others have about human evolution. Genes play a far less significant role in human development as
memes play(ed).
I don't know off the top of my head about your third point, but it must be an easy thing to find out. Did you know that a complete Neanderthal genome has been sequenced?
Edited by CosmicChimp, : fixed title