Evolution, Unity, and Diversity A. Diversity and unity are the dual faces of life on Earth Biological diversity is enormous. Estimates of total diversity range from five million to over 30 million species. About 1.5 million species have been identified and named There is unity in the diversity of life forms at the lower levels of organization. A universal genetic code. B. Evolution is the one unifying biological theme.
Species change over time and their history can be described as a branching tree of life.
Species that are very similar share a common ancestor at a recent branch point on the phylogenetic tree. Less closely related organisms share a more ancient common ancestor.