Identify, which is not the example of homology in evolution.

The correct answer is Option (2) → Eye of the octopus and of mammals

Homologous organs have the same basic structure and origin but may do different jobs. They come from a common ancestor through divergent evolution. Analogous organs do the same job but have different structures and origins. They are the result of convergent evolution.

Option (1) Vertebrate hearts or brains — An example of homology. The heart and the brain of all vertebrates are built on one basic plan inherited from a common ancestor. They differ only in detail from fish to mammal.

Option (2) Eye of the octopus and of mammals — Not an example of homology. The octopus is a mollusc and a mammal is a vertebrate. Their eyes look alike and both form images, but they developed separately in the two groups. So they are analogous organs, a case of convergent evolution.

Option (3) Bones of forelimbs in mammals — An example of homology. The forelimbs of whales, bats, cheetahs and humans do different jobs. Yet all of them have the same set of bones: humerus, radius, ulna, carpals, metacarpals and phalanges.

Option (4) Thorn and tendrils of Bougainvillea and Cucurbita, respectively — An example of homology. The thorn of Bougainvillea helps in defence and the tendril of Cucurbita helps in climbing. But both are modified stems that arise in the same position, so they are homologous.

NCERT Extract:
What Are the Evidences for Evolution? – “… Such similarities can be interpreted to understand whether common ancestors were shared or not. For example whales, bats, Cheetah and human (all mammals) share similarities in the pattern of bones of forelimbs (Figure 6.3b). Though these forelimbs perform different functions in these animals, they have similar anatomical structure – all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs. Hence, in these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry. Other examples are vertebrate hearts or brains. In plants also, the thorn and tendrils of Bougainvillea and Cucurbita represent homology (Figure 6.3a). Homology is based on divergent evolution whereas analogy refers to a situation exactly opposite. Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions. Hence, analogous structures are a result of convergent evolution - different structures evolving for the same function and hence having similarity. Other examples of analogy are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins.”