The Definition of Life

Originally published 9/17/2016.

Lead Image: A diagram of the Xenonucleic Acids (XNAs). It’s like DNA, but better. Source: Wikimedia Commons

Taking the Criteria of Life WAY Too Literally

Biologically speaking, there are seven characteristics for life:

  • Living Things are Composed of Cells
  • Living Things Have Different Levels of Organization
  • Living Things Use Energy
  • Living Things Respond To Their Environment
  • Living Things Grow
  • Living Things Reproduce
  • Living Things Adapt To Their Environment

This list seems like a no-brainer. Can you think of any situation where it may be hard to tell what’s counts as being alive? Certainly not rocks. Or lava. Or the sun.

The big question si normally about viruses. They can’t reproduce on their own, so they technically don’t count as being alive. But let’s take this list very literally for a moment, and see what conclusions we can draw. Are you ready to find out if you’re alive or not?

1. If you have not reproduced, you are not alive
It says it right there in the list. Living things reproduce. My parents are alive, but I am (thankfully) not. My dog is not alive. My brother is not alive. The vast majority of my friends are not alive, and no person is capable of being alive until they go through puberty.

2. If you are asleep, you are not alive
Living things respond to their environment. Do you do this when you’re asleep. If you do, I feel sorry for your roommate.

3. If you don’t learn from your experiences, you are not alive
This is a double whammy. Living things grow (as a person) and living things adapt to their environment. How many times have you stubbed your toe on that very same desk? Sorry–you haven’t adapted, so you’re not alive. Have you ever blamed your own bad behavior on someone else? Sorry, you missed an opportunity to grow as a person. Too bad.

4. If you’re disorganized, you are not alive
Sorry, but color-coding your notes isn’t enough. You have to have several levels or organization, not just one. Alphebetise your books? That won’t cut it. You also have to organize by edition and color.

5. If you’re environmentally-friendly, you are less alive
Sorry, but it says that living things use energy.

6. If you are composed of cells, are you alive?
I was going to come up with a little quip for this one, but the only thing I could think of was a pun on the word “cell” and its various meanings. So let’s try a serious one on for size. We think of life in terms of death. You are not considered alive once your brain can no longer process your five senses, and you cease to sense things. But many of your individual cells are still alive at this point, and each of them is considered alive.

But if we think of life in terms of sensing or not sensing things, then can a cell really be alive? Can it not sense about as many things as a virus can? And if we don’t think of life in terms of what we perceive as sensing things, then what does that tell us about our bodies when we die? Our individual components may still be alive. What about Henrietta Lacks’ immortal cancer cells? What about robots? We could eventually program bionics to mimic our senses (ex. a replacement eye, a prosthetic nose here and there). If we invent an AI that can build other AIs, then isn’t it alive? Does it have to be able to sense things, or can it just be a computer program? What about a program on a loop? It uses energy, it adapts to user input, it can recreate itself. It can “grow” (use up more data)…

​And that, my friends, is what I learned by not paying attention in biology class. The meaning of life is sex, individual sperm and egg cells are alive, and the two halves of your brain are individuals that you may or may not have control over.

Good night.


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