The Common Origin of Organisms
The basis of the study of molecular evolution and taxonomy is the origin of organisms. Although the tree of life shown in Figure was derived from sequences of a single gene, the similarities among organisms' biochemical and molecular properties are greatest for the organisms closely branched on the tree. Thus, human metabolism is more similar to that of chimpanzees, a close relative, than to that of yeast, a more distant relative. Human and yeast biochemistry are more similar to each other than either is to an archael or bacterial organism. The implications of this are important for the application of biochemistry to human disease. It is obviously unethical to do many biochemical experiments on human beings; however, animals or cultured animal cells are similar enough to find principles in common. For example, medical researchers can study the properties of genes that cause disease in mice, and evaluate potential treatments for safety before trying them on humans. Although not foolproof, this principle of similarity has been used continually in biomedical research dedicated to disease treatment and prevention.