A while back, I did a post speculating that if we ever meet aliens, they will have (or will have once had) cancer.
I still think that’s correct. In fact, I have a feeling it can be extended. For example, isn’t it reasonable to suppose aliens will get the flu?
Okay, not the flu per se, but something very much like it. Unless alien life were wildly different from us, we can probably make a few assumptions and deductions:
1) It must have some way to take in energy and excrete waste.
2) That there will be other life around it.
3) That therefore there will be some subset of life that parasitizes other life.
4) That some of that subset will make use of bodily functions to reproduce itself.
5) That if a bodily function can be successfully co-opted by the subset of organisms, in the passage of evolution, it will necessarily become co-opted.
6) That therefore, any alien life we meet will have diseases which are, in essence, similar to our own.
The only exception I can think would be some sort of organism (say an artificial organism) that has constant complete access to its own code. Part of the difficulty being a human is that even if you know what disease you have and roughly where it’s hiding, you can’t do much about it. Herpes, for example, is notoriously good at hiding from the immune system. HIV is known for disguising itself very well. If you could just scan the body for every problem and remove it, you wouldn’t have to worry about disease. Well, unless it were very cleverly made. Then artificial life might very well have a monoculture problem.