Koontz notes that there are over 100 different definitions of life, including NASA’s, hich posits that “the most well-known modern definition is probably NASA’s, which says living things must be “a self-sustaining chemical system capable of Darwinian evolution.”
Actually, “capable of Darwinian evolution” is an unreasonable stricture. A life form could evolve by horizontal gene transfer (as opposed to natural selection acting on random mutation [Darwinism]) and still be very much alive.
But beyond that, most of these definitions of life fall short in another, very subtle way: They are based on the origins of life on our planet. This means our hypotheses for what sentient and conscious aliens look like almost always reflect humankind. You only have to look at a Star Trek episode to see it — humanity likes to make the world in our image, which is partially why in sci-fi and fantasy a lot of the “aliens” look a lot like ourselves. (Okay, and because it’s easier to dress a human up as a humanoid alien)…
If our definition doesn’t even work correctly with the systems we observe on our planet, it’s incredibly likely that in the larger universe there will be systems that break this definition as well. For example, included in most of the 100+ definitions of life is the ability to self-replicate with variation — one of the fundamentals of Darwinan evolution. But it’s perfectly reasonable to picture “supra-Darwinian” life, which arose by pathways that don’t exist on Earth.
For instance, say we find a planet full of aliens who have achieved immortality. The population has been stable for thousands of years, with nobody being born and nobody dying — in other words, there is no self-replication going on. There is no variation. Everything is static. There’s no evolution. Would this alien species be considered living under our current definition? And should it be? Of course, this is a wild theoretical, but as we learn more about the immense universe, this kind of questioning will be important to consider.
Allson Koontz, “Our concept of life is too Earth-centric — alien life might look totally different” at Massive Science
Koontz is right to raise the question. NASA needs to change its definition. Hey, a conference.
But as it happens, we have only life on Earth to work with at present. Let’s keep the balloon tethered.
And honestly, too much of the other stuff is what some of us call “Tales of an Invented God.”