Defining Life – Putting it All Together

This is part of a series: Define Life

I’ve listed the most common views on exactly what life is – now I’ll try to do better. But first, I’ll list my biases:

1. In my opinion, there are a couple of inventions that will likely be created within the next 100 years which I think should be considered life. However, most people who I’ve met disagree. These inventions are:
   • Clanking replicators
     Self-sustaining, fully automated factories made of current human technology, or something not much more advanced. Each “cell” will be easily big enough to see, and would probably come in the form of a small building or a group of robots that can collectively sustain themselves, and even reproduce.

2. Von Neumann probes
   Self-sustaining, replicating starships that would spread through all of space. They would probably be used for four main purposes:
   • Exploration
   • Mining
   • Terraforming
   • Building and maintaining rest stops
3. I prefer to define life by its function, not the details of one implementation. That is, instead of saying that all life has DNA, I prefer to say that it stores all the info needed to run itself, and possibly also all the info needed to reproduce. This is partly due to my first bias, and partly because it makes more sense to me.

Remember the question that I’m trying to answer:
If an inventor says that he’s created a completely new kind of life, that isn’t built on the same biochemistry, etc. as the life that we know of, how can we know whether he’s right or wrong?

Here’s my definition:

Life is a factory that is:

1. Self-sustaining,
2. Fully automated, and
3. Autonomous, in the sense that it doesn’t need an operator to function

To achieve these things, life will usually, if not always, have these attributes:

1. Reproduction
2. Responds to stimuli
3. Adapts to its environment
4. Takes in energy from its environment
5. Takes in materials from its environment, possibly taken from other living things
6. Uses the energy and materials that it gathers to sustain itself and reproduce
7. Repairs itself
8. Stores inside of itself all info needed to run itself and reproduce

Life doesn’t have to do any of these things perfectly. For example, it’s possible to age or get wounds that never fully heal and still be alive, even though life generally sustains itself and repairs itself. It’s also possible, and likely, that one living thing might depend on another living thing to survive. A complete collection of all living things needed to completely sustain all its members is an ecosystem.

The big question now is how good of a definition this is. What are the fuzzy edge cases? If there are any, do they mean that this definition is:

• Bad?
• Incomplete?
• Good, but limited by the vagueness of human language?
• Or do they just mean that it’s possible for something to come close enough to being alive that it’s debatable whether it should be called life?

Off the top of my head, here are some edge cases:

• Ecosystems
  A body made of cells is alive, so does that mean that a group of living things that need each other to survive is also alive? If so, why? If not, why not?
• Societies
  Same argument as for ecosystems, except they’re large groups of people who need each other. Again, if so, why? If not, why not?
• Predators
  They don’t even come close to being able to sustain themselves when they only have raw materials. I’m not worried about this, though, since they just gather materials that have already been pre-processed.
• Parasites
  They’re generally built on the same technology as their hosts, but they feed on another still-living creature. I think that these should be considered alive, for the same reason as predators.
• Viruses
  This is a little more controversial. Even the definition I linked to says that viruses aren’t alive. Under my definition, if predators and parasites are alive, then viruses are, too. They just go dormant when they aren’t inside a host, much as this parasite does. Also, they steal another creature’s factory, instead of making one themselves.
• Prions, and other self-catalyzing chemicals
  Mis-folded proteins that force other proteins to mis-fold in the same way. I don’t think that these should be considered alive, since they aren’t even close to being self-sustaining factories. Why do I say viruses are life, when prions aren’t? Viruses are stripped-down cells, while prions aren’t. Also, a prerequisite to something being automated is having a programmable controller to automate. Viruses have, at very least, a program for an automated factory, while prions don’t.
• Computer malware, and other self-copying software (quines)
  I’m not sure about this one. Whether they are or aren’t, depends on whether the virtual world inside a computer counts as an “environment”, and whether CPU time, RAM, hard drive space, network bandwidth, etc., count as raw materials. They’re either alive, or life-like.
• Memes
  Definitely not, since they bear no resemblance to factories.
• Symbiotes
  Creatures of more than 1 species that live together and work together, and both benefit. They usually are very different from each other, and not in, say, the same genus. The main question here is whether symbiotes that always need each other should be considered one creature or two. I say that each member of a symbiotic relationship is alive, since each is a self-sustaining factory.
• Spirits
  Surely a spirit is alive, but does it fit this definition? I don’t know enough about what exactly a spirit is to give a good answer.

Photo credits:

• Human egg being fertilized
• Implanted zygote
  The zygote photo is “Copyright © 2009 Boots UK Limited and WebMD UK Limited. All rights reserved”, as required by their terms of use