Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Dynamics of Life
What “being alive” means is easily characterized, as we have plenty of specimens to study: life is about growing and reproducing. A living organism is capable of using the environment (sun, water, minerals, other living organisms) in order to change its own shape and size, and it is capable of creating offspring of a similar kind. In technical terms, life has two aspects: metabolism and replication. Metabolism is the interaction with the environment that results in growth. Replication is the copying of information that results in reproduction. Metabolism affects proteins, replication affects nucleid acids.
The statement that "life is growing and reproducing" is convenient for studying life on this planet, life as we know it. But certainly it would be confusing if we met aliens who speak and feel emotions but do not need to eat or go to the restrooms, and never change shape. They are born adults and they die adults. They do not even reproduce: they are born out of a mineral. Their cells do not contain genetic material. They do not make children. Would that still be “life”?
Also, that definition is not what folk psychology uses to recognize a living thing. What is an animal? Very few people would reply "something that grows and reproduces". Most people would answer "something that moves spontaneously". The "folk" definition is interesting, because it already implies a mind.
At the same time, the folk definition does not discriminate in a crisp manner between animate and inanimate matter. A rock can also move. True, it requires a "force" to move it. But so is the case with animals: they also require a force, although it is a chemical rather than a mechanical force. Animals eat and process their food to produce the chemical force that makes them move. The difference between the stone and the animal is the kind of force and where it comes from.
It is not easy to define "life". We know what life looks like on Earth: life is made of carbon, it uses left-handed chemicals, the way to create proteins is coded in DNA and uses four bases and RNA as an intermediary, life makes typos (mutations) when it copies itself, life reproduces, it grows, and it dies. While there might well be billions of Earth-like planets in the universe, "finding" life outside the Earth is not trivial: how will we recognize it as "life" if it doesn't look like Earth life? What exactly are we looking for? Something that reproduces? something that grows? something that is made of the exact same material as life on Earth? We already have examples of each of these, whether software or crystals or lab chemicals, that we don't consider "alive". It seems that we will recognize as "life" only something that has all the properties that life has on Earth. There is an argument that this is very likely to have happened on those Earth-like planets. The support to this thesis comes from the fact that some traits did evolve independently more than once on Earth. We now that flying evolved at least four times (insects, birds, etc) and that eyes evolved independently in more than ten families of animals. Therefore one would be tempted to conclude that, for reasons that we still don't know, life tends to follow a deterministic curve that recreates more or less the same creatures or at least the same traits. At the same time, if that is the case, it is not clear why dinosaurs evolved only once: why didn't they evolve again after the mass extinction? The Earth has never seen such giant creatures again. The contrary argument is that fixing nitrogen, a vital function for plants, never evolved (it is carried out in symbiosis with bacteria). Therefore life is not that deterministic, after all; and in that case we don't really know "what" evolved on other Earth-like planets.
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