Do you think we could/will ever have two dominant[prime] species?

[AFTT47]

I can think of two plausible ways for separate dominant species to evolve out of humanity:

1.  Genetic engineering - humans begin to implement high degree of genetic menipulation and eugenics until a population sufficiently altered as to represent one or more new species arises.   This could happen relatively quickly on a scale of decades or centuries at most. Whether humans will eradicate them, they will eradicate humans, they will eradicate each other, or some will coexist either peacefully or precariously, is hard to say.  But I give high likelihood it will happen within a few centuries.

I agree that this is a possible scenario. There should be no doubt that technology will advance to the point where we are able to dramatically improve ourselves. Some people will reject such "improvements", seeing it as dehumanizing. What will happen then is anybody's guess. I doubt the improved humans would have any ambitions against the old. I believe they would take advantage of resources in the solar system and move on. The old humans however, might well fear them and instigate the kind of terrorism we see today - but on a much worse scale. That could be a very ugly time.