The Elements of Evolution (28-1) Analogues and Homologues

Analogues and Homologues

It seems that Nature has taken pleasure in varying the same mechanism in an infinity of different ways. ~ French philosopher Denis Diderot in 1753

Evolutionary developments that can be traced in lineage are homologues. Similar traits that arise independently are analogues.

Homologues illustrate the incremental nature of evolution. Analogues demonstrate how purpose-driven evolution results in similar adaptations for unrelated organisms. Convergent evolution is the umbrella term for analogues.

Eyes are exemplary of both. As a homologue, monkey and human eyes share a long lineage, with human eyes a modest refinement. By comparison, compound insect eyes are analogues: the same function is achieved, albeit quite differently.

The wings of pterosaurs, birds, and bats differ considerably, yet each is of a forelimb shared by all tetrapods, and so are homologues. Wasp wings are analogues to these.