(a) Analogy (b) Homology (c) Analogy
Work Step by Step
(a) Porcupines and cacti are not related, except for very distantly in the relation of all life forms to each other, and their spines are unique structures, which serve largely different evolutionary purposes. (b) Humans and cats have homologous skeletal structures as they are both mammals; Homologous skeletal development is seen throughout this class even when their overall structure is very different. For example, the limbs of a human and the fins of a whale have homologous underlying skeletal structures. (c) As in part (a), owls and hornets are only very distantly related, and their wing structures are fundamentally dissimilar from one another despite serving similar functional roles.