What is Life?

I�d like to start this thread so we can talk about what exactly makes up life. The debate has died down in the scientific community simply because its is so hard to define and nothing further can really be gained from debate. This however doesn�t mean we at ATS can�t take up the subject, and maybe ever come up with a few new things.

Here are a few things often associated with life to get things started�

Reproduction
Cells
Genetic Code (or code of some kind, such as DNA or RNA)
The ability to communicate (for intelligent life)


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I�d like to start with some of my own thoughts.

Often times it is debated weather or not viruses are alive. This is because they are so much more simple than a single cell. Just a strip of DNA (or RNA) inside a protein. The DNA only codes for two things basically, its own duplication, and the protein that holds it. Once a virus invades a cell it just reproduces until so many are within the cell that it kills the cells and spreads as the cells dies and collapses.

Is this a living thing? Virtually all scientist would say a single protein is not alive. Many would say a single strip of DNA is not alive. But put the two together and they are a life form?

I think this debate is at the heart of the question, what is life? Some where we draw a line between just chemistry and living organisms. The virus doesn�t think, or strive for anything. It has no need to reproduce, feed, or will to live. Rather, it just exist, floating around in our world. If it happens to bump into a cell and its protein matches up with the cell wall, it slips inside. Even once in a cell it just hangs out, the DNA floating around the cell. If the cells organelles happen to bump into the DNA they mistake it for its own and start replicating it.

This is the issue. Everything in a cell is just chemistry. Nothing moves or happens with a sense of will. Its just random chemicals that float around and as they bump into each other reaction occur. Sure there are entire ultra complex pathways of reactions, but any one reaction would also occur if you took the starting chemicals, put them in a jar, and gave it a good shake. Yet, even though we now understand almost all of cellular biology, and see it as natural chemical reactions, we still call a functional living cell alive.

I think defining life is virtually impossible.

Yes, it is very difficult to define life. Science hasn't come up with a final definition after all these years. It's just too difficult. It is possible though to decide on a few things that should at least be present in the definition. These are:

- Reproduction
- Growth
- Reactions to environment

Other things, like gas exchange are still under debate. Gas exchange would rule out artificial life. The problem with the three things above, is that those would also define fire as life. Fire reproduces, it grows and it reacts to its environment. There are more things needed to really define life. If I knew which, I would probably be writing a book or article about it right now.

Indeed. Are AI's alive? I would like to think so. We have mroe and better definitions of death. However, like the definitions of life, they are arbitrary.

IS the perosn dead when they reach upper braindeath? Is the person dead when their autonomical functions cease?

DE