Molecular Evolution Activities



Online Document

    [Summary] [PDF 4.2MB]

    In this paper, Zuckerkandl and Pauling set out show that phylogenies can be reconstructed by comparing the sequences of homologus hemoglobin and myoglobin chains in a diverse array of species. They find these molecules so interesting because, unlike cytochrome c, globins appear to have very few invariant amino acids. The paper begins, however, with an effort to rebut their critics from two major scientific communities: organismal evolutionists on one hand (especially G.G. Simpson [see Simpson 1964]), who argue that evolution takes place at the level of the whole organism; and "pure" biochemists on the other, who see no value in reconstructing phylogenies at all. A major portion of this article is devoted to theorizing about what makes a peptide site variant or invariant. They also take up the issue of whether it is possible to express evolutionary transformations at the molecular level simply as a function of time. They conclude that, "So far, the refutations of the time function [e.g. Mayr and Simpson's arguments that evolution is too complicated and historically contingent] have been weaker than its formulations." As such, they concur with Margoliash and Smith that the use of numbers of differences between polypeptide chains in order to determine evolutionary relationships is valid. In applying this method to their globin data, they find that there seems to be a constant rate of evolution in most non-functional polypeptide regions. This leads the to the conclusion that "there may thus exist a molecular evolutionary clock." (jda)

