evolutionary relationships from degrees of similarity. Using the same logic, other biologists examine similarities in the functions of different organs, in the development of embryos, or in behaviors among different kinds of organisms. These investigations provide evidence about the evolutionary pathways that connect today’s organisms to their common ancestors. Hypotheses based on this evidence then can be tested by examining the fossil record.
Sometimes, separate lineages independently evolve similar features, known as “analogous” structures, which look like homologies but result from common environments rather than common ancestry. For example, dolphins are aquatic mammals that have evolved from terrestrial mammals over the past 50 million