The evolution of similar traits in unrelated species under similar environmental pressures is called convergent evolution.
Convergence occurs when natural selection repeatedly favours comparable solutions to comparable ecological problems. The species involved do not inherit the trait from a recent common ancestor that already possessed it; instead, they evolve similar features independently. These similarities are often called analogous traits.
A classic example is the streamlined body shape of sharks and dolphins. Sharks are fish, while dolphins are mammals, but both evolved a similar form for efficient movement through water. The wings of bats and birds are another example of similar functional adaptations that arose in separate lineages. Australian marsupials and placental mammals also evolved strikingly similar ecological forms in some cases.
Convergent evolution differs from divergent evolution, in which related organisms become increasingly different. It is also distinct from parallel evolution, a term often used when closely related lineages independently evolve similar traits. Adaptive radiation describes one ancestral lineage diversifying into many forms, rather than unrelated lineages arriving at similar solutions.