One thing you are getting into, DJ, is the very challenging topic of "What is a Species?" or "Species Concept" and just a caution (from a biologist) that this is itself a very challenging topic within the field of biology. Suffice to say there are many ways to define what a species is. Of course Wikipedia can give you a good treatment of the topic. There are over 10 different ways listed there to define a species: http://en.wikipedia.org/wiki/Species Good luck!
The story of Genesis obviously has elements both of allegory/poetry while at the same time speaking truth about God, and humanity and their relationships. The fact that the human species (however it is defined) has an evolutionary origin should not negate the need of man for repentance, and obedience to God's law, which is "written on our hearts." It also should not negate the truths about Christ's role in salvation. We are now free to better interpret the meaning of Genesis/original sin/the Fall, etc based on our better knowledge of nature, that should help us better interpret the scripture. Just like when observations led folks to realize the earth was not the center of the universe, that led to better theologies of heaven/hell and the like. (in other words, hell is not down there in the earth, very far from the "heavens."