[aluren]

DNA is nothing like source code. Why do people keep repeating this analogy.

At any rate, cell differentiation/compartmentation within a tumor has been observed, so things do get blurry indeed. It's also worth noting that there isn't a single definition of 'species' and it's all just semantics that changes depending on your field. (The traditional 'inter-fertile over two generations' you learn in high school is helpful but doesn't stand up to many observations.) Ultimately a species is what biologists say is a species.