"What is Evolution?"
"Biological evolution consists of change in the hereditary characteristics of groups of organisms over the course of generations. Groups of organisms, termed populations and species, are formed by the division of ancestral populations or species, and the descendant groups then change independently. Hence, from a long-term perspective, evolution is the descent, with modification, of different lineages from common ancestors. Thus, the history of evolution has two major components: the branching of lineages, and changes within lineages (including extinction). Initially similar species become ever more different, so that over the course of sufficient time, they may come to differ profoundly."
"All forms of life, from viruses to redwoods to humans, are related by unbroken chains of descent. The hierarchically organized patterns of commonality among species "such as the common features of all primates, all mammals, all vertebrates, all eukaryotes, and all living things" reflect a history in which all living species can be traced back through time to fewer and fewer common ancestors. This history can be described by the metaphor of the phylogenetic tree. Some of this history is recorded in the fossil record, which documents simple, bacteria-like life as far back as 3.5 billion years ago, followed by a long history of diversification, modification, and extinction. The evidence for descent from common ancestors lies also in the common characteristics of living organisms, including their anatomy, embryological development, and DNA. On such grounds, for example, we can conclude that humans and apes had a relatively recent common ancestor; that a more remote common ancestor gave rise to all primates; and that successively more remote ancestors gave rise to all mammals, to all four-legged vertebrates, and to all vertebrates, including fishes."