I’ve heard that carbon is not necessarily the best basis for self replicating structures. Silicon is able to form a lot of similarly complex bonds that carbon is with a similar chain of reactions to our own. I don’t know if another life form from the ground up would even have diseases, although I guess cancer is pretty likely in any self replicating system due to cosmic rays. That would make it pretty hard to space travel though, one would expect their repair mechanisms to far excel beyond the durability of our own, which is actually pretty crap and easily confused with symmetrical DNA chains, excessive damage, repeating sequences, etc. There are other animals on earth that have better repair systems in place than us allowing them to live virtually forever, but none are mammals. Biological Immortality Wiki