In a recent posting John asks about the substitution rate in 16s rRNA and
whether it can be used as an indicator of time of separation.
Well, many people have used %difference of 16s rRNA to date divergence of
species. The first paper I am aware of on the subject is Ochman & Wilson.
J. Mol. Evol. 26:74-86. 1987. They suggested that 1% divergence corresponded
to about 50 million years. Other people have used 16s rRNA divergence
to estimate the date of species divergences. I'm not sure what the lower
limit of divergence people have tried to estimate. Whether you believe
the estimates or not is a different question. The 95% confidence limit
on the estimates may be very very broad (David Hillis has done some
work related to this but I'm not sure of the citations).
Jonathan A. Eisen
Department of Biological Sciecnes
Stanford, CA 94305-5020