Which characteristics are similar due to a shared common ancestor?

Homologous characteristics are traits that are similar in different species because they share a common ancestor. This means that despite possibly differing in function or appearance due to adaptation to different environments, the underlying structures are fundamentally similar due to their shared evolutionary origin. For example, the forelimbs of humans, whales, and bats have different functions—grasping, swimming, and flying, respectively—but the bone structures are similar, indicating that these species descended from a common ancestor that had a similar limb structure.

In contrast, analogous characteristics result from convergent evolution, where species develop similar traits independently due to similar selective pressures, not because of a shared ancestry. This can often lead to confusion, as these traits may perform similar functions but do not showcase a common evolutionary path. A synapomorphy refers to a trait shared by two or more groups that originated from a common ancestor, but it is a more specific term used within phylogenetics to identify shared derived characteristics that help in determining evolutionary relationships.