all available dna sequences for coi ( 108 head and 58 clothing lice ) , 18s rrna ( 10 head and 12 clothing lice ) , ef-1 ( 25 head and 9 clothing lice ) , and rpii ( 25 head and 10 clothing lice ) for p. humanus and the outgroup p. schaeffi ( chimpanzee louse ) were downloaded from genbank ( available as supplementary table s1 , supplementary material online ) . all sequences were aligned by hand using se - al v2.01a11 ( http://tree.bio.ed.ac.uk/software/seal/ ) , with the 18s rdna aligned to secondary structure ( gillespie 2004 ; gillespie et al . substitution rates ( table 2 ) for the four genes were estimated in beast v.1.5.3 ( drummond and rambaut 2007 ) . rates were calibrated by placing an exponential prior distribution ( lower bound = 5 ma , mean = 5.5 ma ) on the divergence of p. humanus ( human ) and p. schaeffi ( chimpanzee ) lice that reflects conservatively recent estimates for the divergence of their hosts ( kumar and hedges 1998 ) . each gene was analyzed using a range of substitution and clock models , as well as tree priors , with posterior estimates made from the model that best fit the data as determined by marginal likelihoods estimated in the program tracer v1.5 ( http://tree.bio.ed.ac.uk/software/tracer ) . markov chains were run for at least 100 million generations , sampled every 10,000 generations , and the first 10% of samples were discarded as burn - in . models of substitution , likelihood scores , and mean substitution rates per gene calculated in beast . between site rate variation partitioned by codon position ( cp ) . multilocus bayesian i m coalescent analysis was performed on the p. humanus sequences using the program i m ( hey 2005 ) . all analyses used the hky substitution model , whereas priors on model parameters were broad uniform distributions conservatively estimated from preliminary runs . markov chains were run for > 200 million generations and replicated 8 times to ensure convergence . a louse generation time of 21 days ( 18 generations per year ) and the substitution rates in table 2 were used to convert parameter estimates from mutational to demographic units .
clothing use is an important modern behavior that contributed to the successful expansion of humans into higher latitudes and cold climates . 
 previous research suggests that clothing use originated anywhere between 40,000 and 3 ma , though there is little direct archaeological , fossil , or genetic evidence to support more specific estimates . 
 since clothing lice evolved from head louse ancestors once humans adopted clothing , dating the emergence of clothing lice may provide more specific estimates of the origin of clothing use . here , we use a bayesian coalescent modeling approach to estimate that clothing lice diverged from head louse ancestors at least by 83,000 and possibly as early as 170,000 years ago . 
 our analysis suggests that the use of clothing likely originated with anatomically modern humans in africa and reinforces a broad trend of modern human developments in africa during the middle to late pleistocene .