Online Document
- Emile
Zuckerkandl and Linus Pauling, "Evolutionary Divergence and Convergence
in Proteins," in Evolving Genes and Proteins, eds. V. Bryson
and H. Vogel (New York: Academic Press, 1965). pp. 97-166.
[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)
This page was written by Michael Dietrich and Jay
Aronson. It was last updated on May 15, 2004.
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