Introduction

Figure 20.1 The life of a bee is very different from the life of a flower, but the two organisms are related. Both are members of the domain Eukarya and have cells containing many similar organelles, genes, and proteins. (credit: modification of work by John Beetham)

Chapter Outline

20.1 Organizing Life on Earth

20.2 Determining Evolutionary Relationships

20.3 Perspectives on the Phylogenetic Tree

This bee and Echinacea flower (Figure 20.1) could not look more different, yet they are related, as are all living organisms on Earth. By following pathways of similarities and changes—both visible and genetic—scientists seek to map the evolutionary past of how life developed from single-celled organisms to the tremendous variety of creatures that have germinated, crawled, floated, swam, flown, and walked on this planet.

New species are discovered with frequent regularity, but it’s not too common to discover a new large mammal. However, that’s what scientists did in Australia when they named a new species of cetacean the Australian humpback dolphin, Souse sahulensis. The dolphin had originally been classified as another closely related species, but a closer look at its coloration, skeletal structure, habitat, and DNA determined that it was in fact a separate species.