Jimmy Akin with a Fascinating Discussion of Adam and Eve
Jimmy's posts are always top notch, and this one does not disappoint. The comments discussions are fascinating too. The main discussion lies with the origination and subsequent breeding of Adam and Eve and their descendants, and how this could fit in with the theory of evolution.
My personal take is that I don't think that a human beings immortal soul is (or can be) inherited - it is created directly by God each time. So it would be possible to posit a race of hominids who gradually evolved (not saying I necessarily believe this - I'm actually more or less an agnostic on macroevolution) and at some point God decided to infuse an immortal soul into two of them.
The genetic materials of Adam and Eve were probably optimum to avoid interbreeding problems, though as Jimmy says, the dangers of interbreeding are somewhat exaggerated anyway.
Another interesting theory, which I don't think would be necessarily a problem for our faith, though, is that humans with immortal souls mated with the biologically identical (or nearly identical) hominids that did not have the immortal souls. The immortal soul is created directly by God, so he simply chose to infuse souls into those who were descended from one with an immortal soul. In a handful of generations or so, everyone living would then have an immortal soul.
Anyway, it's all makes for a very nice cognitive chewy!