Convergent evolution: unrelated lineages independently evolving similar traits in response to similar selective pressures.

The eye evolved independently at least 40 times. Dolphins and ichthyosaurs (a Mesozoic reptile) developed nearly identical body plans for similar aquatic lifestyles, from completely different starting points.

The implication: evolution is not purely contingent. Given similar environments, similar solutions recur. This doesn't make evolution deterministic — the specific molecular implementation differs — but it does suggest that the design space is structured.

See: [[phenotypic-plasticity]], [[@dave/on-abstraction]]