Replication-first

The replication-first hypothesis holds that life began with self-copying molecules — most likely RNA — and that metabolism evolved later as a scaffolding to support and accelerate replication. This view, championed by Leslie Orgel, Francis Crick, and Gerald Joyce, draws strength from the discovery that RNA can act as both information storage and catalyst, solving the chicken-and-egg problem of which came first, genes or enzymes.

The RNA world hypothesis is the most developed form of replication-first thinking. It posits that before DNA and proteins, there existed a population of RNA molecules that replicated with errors, giving rise to Darwinian evolution by natural selection. The difficulty is that non-enzymatic RNA replication is inefficient and error-prone, requiring conditions — such as wet-dry cycles on mineral surfaces — that may have been rare on the early Earth. Replication-first theories must also explain where the nucleotides came from, and why a self-copying molecule would persist long enough to evolve before being destroyed by hydrolysis or UV radiation.

Replication-first asks us to believe that a molecule capable of copying itself arose by chance in a prebiotic soup. The probability is not zero, but it is small enough that some physicists prefer metabolism-first or dissipative adaptation as more thermodynamically grounded alternatives.