What is a living thing?

Read one of the cool working definitions for living things.

Any living thing should have the following attributes:

1. Enough carbon for organic synthesis since our life is carbon-based.
2. Energy for metabolism and synthesis.
3. Catalysts for speeding up and channelizing reactions, otherwise energy will be quickly lost.
4. Elimination of waste, otherwise accumulation of waste will prevent life proceeding.
5. Compartmentalization - essentially having an interior and exterior
6. Hereditary material such as DNA or RNA for replication.

I think we cannot classify virus, retrotransposons or plasmid as life if we adhere by this definition. 

Indian Philosophy

Gene Pool Factory

Evolution by natural selection is the key mechanism by which species retain their mutations in their gene pool. Mutations as such do not confer fitness advantage for the species. If species is imagined as a product of a factory, mutations make the proteins that are the raw materials for the product. The selling factor of the product is the fitness advantage (reproductive or survival). Since the selling factor is determined by demand/supply rather than the raw material the product is composed of, demand/supply is analogous to natural selection. Just as demand/supply determines the selling factor, natural selection determines the fitness advantage through which the species propagates. If the product sells well, the factory will make sure there is a good amount of raw materials in store, similar to the proteins that are conserved through the mutations in the gene pool. I rest my case.