The jellyfish:
http://en.wikipedia.org/wiki/Biological_immortality#Jellyfish

I didn't actually contradict myself. I said human beings would never become immortal, and I stand by that belief. That jellyfish is potentially immortal, and if you mixed its genes with ours you might end up with an immortal human, but that's assuming the "gene mixing" is even possible in the first place. And if it is possible, and we learn how to do it, who's to say we actually will get the chance to do it? Think of the controversy that would spawn if someone announced they were going to create a new subspecies of humanity. And of course there is still the question, if you add unfamiliar genes to a human being, is it even really human any more?

Also this is a learning process for me, I'm not pretending to be an expert. I'm just telling you what I've read so far, so my stance may change on this issue very rapidly. I suppose you can say I'm following ideas as I post.

EDIT: Oh yes, there are other issues. The jellyfish is supposedly immortal, but we reached that conclusion through extrapolation. It appears to be immortal from what we've seen of it so far, but perhaps there are other processes involved in the fish's biology that will prevent it from living forever, regardless of its outer conditions?