Oxygen flooded into the atmosphere as a pollutant, even a poison, until natural selection shaped living things to thrive on the stuff and, indeed, suffocate without it.

All life evolves by the differential survival of replicating entities

What are all of us but self-reproducing robots? We have been put together by our genes and what we do is roam the world looking for a way to sustain ourselves and ultimately produce another robot child.

But, however many ways there may be of being alive, it is certain that there are vastly more ways of being dead, or rather not alive.

We are machines built by DNA whose purpose is to make more copies of the same DNA. ... This is exactly what we are for. We are machines for propagating DNA, and the propagation of DNA is a self-sustaining process. It is every living object's sole reason for living.