Molecular Evolution Activities



Online Document

G. G. Simpson, "Organisms and Molecules in Evolution," Science 146 (1964), 1535-1538.
[Summary] [PDF 1MB]

In this article, Simpson critiques the reasoning that many molecular biologists use when inferring phylogenetic relationships from molecular data. He points out that while calculating the rate of evolutionary change in amino acid sequences requires paleontological data, many molecular biologists do not acknowledge the fundamental importance of morphological and anatomical data. Instead, they believe that they can make evolutionary claims based solely on molecular data. For Simpson, a paleontologist and "architect" of the neo-Darwinan evolutionary synthesis, this reduction of evolution to molecular mechanisms ignores the fact that most meaningful evolution (i.e. that which is a result of natural selection) occurs at the organismal level. He also critiques the approach of workers like Zuckerkandl and Pauling, who seek to reconstruct phylogenies based solely on sequence imformation about one or two proteins. He argues that this approach captures the evolutionary history of only a tiny part of a very large and complex organism, not that of the organism itself. He further points out that calculating steady rates of evolution at the molecular level depends on the hypothesis that the polymorphism in question is selectively neutral. Simpson unequivocally states, "so far every supposedly neutral gene that has been adequately investigated has turned out not to be neutral." Ultimately, he argues that if one is to understand the process of evolution in any meaningful sense, it is necessary to synthesis the molecular approach with the phenotypic approach so that changes at the level of proteins can be understood in the context of selection at the level of the whole organism. Simpson concludes by postulating that there is a feedback mechanism through which the interaction of organism and environment affects changes at the molecular level. This mechanism operates through natural selection of populations of individuals. Thus, molecules become the messengers of selection rather than entities that evolve hidden from its influence. (jda)


This page was written by Michael Dietrich and Jay Aronson. It was last updated on May 15, 2004.