concept

Convergent evolution

When separate lineages independently evolve the same feature because the environment pushes them toward the same solution - like the streamlined torso of a dolphin, an ichthyosaur, and a shark, three distant lineages all arriving at a fishlike shape because water imposes one efficient form on anything that swims fast. Convergence explains simple, environment-dictated traits, but it is implausible for complex, arbitrary ones - those are usually a sign of shared inheritance instead.