The concept of the molecular clock has revolutionized the field of
evolutionary studies. DNA and proteins contain information about evolutionary
history in the sequence of their components, very much in the same way
that sequences of English letters and words contain information about meaning.
DNA (and protein) sequences can thus be used for reconstructing evolutionary
history and timing events of the past. How good is the clock?
My colleagues and I have analyzed the gene that codes for superoxide dismutase (SOD ) and have found that it is a very irregular molecular clock. The rate of evolution of SOD in mammals, over the last 100 million years, appears to be five times faster than it was in the more remote past, in lineages going to insects, plants, or microorganisms. We are exploring new models of the molecular clock and are sequencing the DNA region containing the SOD gene in a number of species in order to test the models.
Authors: Lee, Y.M., D.J. Friedman, and F.J. Ayala.
Date: 1985.
Source: Superoxide dismutase: an evolutionary puzzle. Proceedings
of the National Academy of Science (USA).