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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.
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