CBSE Class 10 Science 2017 · Paper 31/2/1 · Question 14

Homologous organs, which have the same basic structure but different functions, are used. For example, the forelimbs of a frog, a lizard, a bird and a human all have one bone in the upper arm (humerus), two in the forearm (radius and ulna, fused into one in the frog), a group of wrist bones, and bones of the palm and fingers, although they do different jobs: propping up the body and cushioning landing (frog), walking (lizard), flying (bird) and grasping (human). A detailed design shared by organs doing such different jobs was inherited from a common ancestor, so it shows that these animals are related; the more such characteristics two species share, the more closely they are related. By contrast, the wings of a bird and a bat do the same job but are built differently; such analogous organs do not show a close relationship.