Definition
Self-replication is the capacity of a system to produce copies of itself. Biological cells self-replicate via DNA replication and division. Computer viruses self-replicate by copying themselves into new files. Von Neumann (1948-53) showed that any self-replicator must have a description-plus-constructor-plus-copier architecture; otherwise the recursion does not terminate.
Why it matters
How it works
A self-replicator factors into three components. The description D is a finite, copyable, non-executable representation of the whole system. The constructor C reads descriptions and builds the systems they describe — C is universal in that it can build anything described in its description language. The copier K copies descriptions. The whole replicator is (C, K, D) where D describes (C, K). To replicate: C reads D and builds a new (C, K); K copies D; the new (C, K) plus the copied D form the replicated system.