ABSTRACT
Although he was not the fi rst to propose that life evolved over time, Charles Darwin was the fi rst to lay out a detailed mechanism for evolution, supported by voluminous evidence (Figure 8.20). Darwin based his theory of evolution on two fundamental principles. First, he proposed that the organisms alive today descended from ancestral species. He called this view of life descent with modifi cation. Second, he suggested a mechanism by which such descent could occur. He called this mechanism natural selection, and today it is understood that natural selection is the primary driving force behind evolution.
