I imagine the stereotypical science nerd who also loves anime actually considers the existence of catgirls to be emblematic of a new, brilliantly fruitful era of genetic engineering gone wild. You know,
wild.
The dull hard sci-fi nerds can shove off. As a rule don't like anime anyway.
So yeah.
Well, that's the fun, lolanimelogic kind of answer, but the boring truth is probably a simple case of memetic mutation, from the "God Kills a Kitten" punchline to something more anime-flavored. But I think you already knew that.