… is there anything that must be true of all life, wherever it is found, and whatever the basis of its chemistry? … if I had to bet, I would put my money on one general principle. This is the law that all life evolves by the differential survival of replicating entities. The gene, the DNA molecule, happens to be the replicating entity that prevails on our own planet. There may be others. If there are, provided certain other conditions are met, they will almost certainly tend to become the basis for an evolutionary process.
Replicators and vehicles
“ One way of sorting this whole matter out is to use the terms ‘replicator’ and ‘vehicle’. The fundamental units of natural selection, the basic things that survive or fail to survive, that form lineages of identical copies with occasional random mutations, are called replicators. They generally … gang together in large communal survival machines or ‘vehicles’. … A body, then, is not a replicator; it is a vehicle …”
replicator - an entity that passes on its structure largely intact in successive generations.
interactor - an entity that interacts as a cohesive whole with its environment in such a way that this interaction causes replication to be differential. ... selection - a process in which the differential extinction and proliferation of interactors cause the differential perpetuation of the relevant replicators.
Replicators and interactors are the entities that function in selection processes. Some general term is also needed for the entities that result from successive replications:
lineage - an entity that persists indefinitely through time either in the same or an altered state as a result of replication.