I did not mean to imply that it is possible. It’s just not that easy. The definition of the taxonomies is so hardly rooted in a single statement that defines them. Two animals can be put inside a genus if they can reproduce and form a fertile offspring. XXelianXX’s answer puts this in a simpler manner. Early humans bred with Neanderthals (different species – Homo neanderthalensis). It is the way we classify them.
