That's surprisingly deep stuff from the two Raphs - it must really be a bummer, being the only four of your kind in existence. No way to reproduce, no way to pass on your legacy, no next generation - when you're gone, you're GONE. Bummer. That being said, I find it difficult to believe that, in a world with all sorts of other mutant animals, there are only the four mutant turtles. I mean, cat mutants, shark mutants, this-that-and-the-other mutants - why aren't there any more turtles? I don't know what is causing all these other mutants to pop up - I mean, just how much mutagen IS there? - but if they still are, I should think that at some point some more turtles would, too, especially if the cities are being flooded - expansion of oceans means a lot more amphibians and marine animals.