Two animals that share a homologous trait are humans and bats. The bones that make up a humans fingers and the wings of a bat are inherited from a common ancestor. Both are vertebrates, whose oldest ancestors were fish, but from a later point are descended from amphibians and reptiles which both had fingers. Humans obviously use their fingers to handle and hold things while the same bones in a bat are used to help the bat fly. Although they do not share the same purpose, they were inherited from the same ancestors.
Birds and insects both have wings, but that does not mean that they were inherited from a common ancestor. When comparing the wings of birds and insects, you will actually find more differences than you will similarities. Birds have bones in their wings while insects do not. Birds have one set of wings while insects have two. The wings of a bird are covered with feathers while the wings of an insect are covered with scales. One of the few similarities between them is that they are used to help with flying. The birds and insects evolved with wings because of a need for flight not because they are both descended from a common ancestor.
Good opening description of your homologous pairings and I liked how you walked out the line of argument from ancestry. Well done.
ReplyDeleteOne caution: Be careful about choosing your words because they really matter in science. Amphibians and reptiles had digits, not fingers, a term limited to primates and perhaps specifically to humans.
Good description on your analogous trait. You say that they evolved wings because it was advantageous for them to do so, not because of inheriting them from a common ancestor. Good. But saying so is not evidence of the fact. So what do we know about bird evolution in particular that helps us with this problem? When did birds evolve? And how do we use that information to demonstrate that these are indeed analogous traits, not inherited from a common ancestor?