Few studies have tested between these two competing hypotheses.
This is partly because of the strong correlations between BS, basal metabolic rate, and GT; e.g., mammals with relatively larger BSs usually have longer GTs and a lower basal metabolic rate.
Of the work that has addressed the alternatives, Mooers and Harvey (32) found that age at first birth in birds was significantly related to the rate of molecular evolution in DNA–DNA hybridization data, but BS was not.
A genome-scale study in mammals found that GT better explained variation in base pair substitutions than a BS model (18).
Currently, there is no consensus as to whether the GT or BS hypothesis is a better fit to the observed variation in evolutionary rates (ref. The GT hypothesis assumes that most germ-line mutations occur during DNA replication.
Species with longer generations go through fewer DNA replications and accumulate fewer mutations due to replication errors.
Many studies have invoked the GT hypothesis to explain rate variation (3, 4, 6–8, 10, 18, 24–27).
There is no relationship between AFR and first and second codon positions.The strepsirrhines are advantageous for testing between the BS and GT hypotheses for a number of reasons.First, the strepsirrhines are a diverse radiation with four sets of sister taxa that have clear BS differences (Fig. Second, each of these sister pairs has a fairly recent last common ancestor ( Branch lengths were estimated for the aggregated datasets for all available sister pairs under two different models of molecular evolution (Table S1 and Table S2).In the BS hypothesis, species with a larger BS will exhibit slower rates of molecular evolution.Evidence supporting the BS hypothesis comes from work across a very broad range of taxa (19, 21, 22, 28), although the effect has been disputed (29–31).