Natural selection provides the scientific explanation for the history of life on earth as depicted in the fossil record and in the similarities evident within the diversity of existing organisms. The proportion of individuals that have advantageous characteristics will increase. Discuss the relationship and significance of genetic variation, natural selection, and the ability to reproduce. The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions, and a great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment. Examples could include exposure of bacteria to UV radiation or aquatic organisms to chlorine.
Molecular evidence substantiates the anatomical evidence for evolution.
Additional detail about the sequence in which various lines of descent branched off from one another and the degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences. Life on earth is thought to have begun as simple, one-celled organisms about 4 billion years ago. During the first 2 billion years, only single-cell microorganisms existed, but once cells with nuclei developed, increasingly complex multicellular organisms evolved. Organisms are classified into a hierarchy of groups and subgroups, based on structural similarities and evolutionary relationships. Use a taxonomic key to classify different species of trees and suggest possible evolutionary links between species.