Evolution of species was preceded by an analogous stepwise process of molecular evolution. Selection is a mathematical consequence of the dynamics of self-reproducing systems of this kind. Eigen's experiments with RNA proved that under suitable conditions a solution of nucleotides give rise spontaneously to a molecule that replicates, mutates and competes with its progeny for survival. The replication of RNA appears to be the fundamental event around which the rest of biology developed. First genes were created, then proteins, then cells.
Cells simply provide physical cohesion.
All the historical papers on the subject, from Barbara Hayes-Roth to Nii. Hayes-Roth's opportunistic and incremental model of reasoning contemplates many independent agents cooperating to find the solution to a problem. Each specialized agent is triggered by information written by other agents on a blackboard and each agent can in turn write information for other agents on that blackboard. By matching necessary and possible actions the system determines which agents are active at any time. The computational advantage of this model of inference is that only actions that are relevant to the solution of the problem are taken into consideration.