Does Extra-Terrestrial Life Exist?

Why the answer is probably yes, but why that also means space-faring alien civilizations are almost certainly absent

Image credit: NASA

As most people seem to form their opinions based on whatever movies and TV shows they’ve seen, let’s begin by stating the obvious: at present, we have precisely no evidence to suggest that extra-terrestrial life exists. Furthermore, if extra-terrestrial life (henceforth ETL for the sake of brevity) does exist, we have precisely no reason whatsoever to imagine that any of it would be capable of fashioning technologically sophisticated societies. So for those who like to fantasize about being probed by human-like aliens who travel hundreds of light-years merely for the pleasure of forcing a digit past the clenched sphincter of a human being, it’s time to leave this article and look elsewhere for repressed homoerotic material.

Now that we’ve cleared the room, let’s begin our consideration of ETL based on what slender knowledge currently available to us. From the outset we must acknowledge that we still don’t have a clear picture of how life emerged on Earth; therefore it’s impossible for us to be categorical about anything. We can’t even agree on a rock-solid definition of what we mean by the word life, because even here on Earth we’re defeated by the abundance of variety.

When I was in my teens, most biology textbooks attempted to define life in the following way: a living creature can respire (convert potential chemical energy into energy released to perform some work within the cell), can reproduce (make copies or semi-copies of itself in order to push its DNA forward into the future), and can exhibit at least partial homeostasis (maintain a relatively stable internal environment that buffers external changes). Sounds lovely, except that it leaves us with the question: is a virus alive? It exhibits the ability to reproduce by means of commandeering the cellular mechanisms of its hosts, and it certainly exhibits at least a partial homeostasis. But it doesn’t respire. Is two out of three good enough? This may seem an abstract question, but what if we found evidence of viruses on Mars? Would we throw up our arms in jubilation and declare that we’d found ETL? Or would we say, “no life on Mars” instead?