of the phylogenetic tree of the primates indicated cospeciation of sfv and the primate hosts, as well. a strong linear relationship was found between the branch lengths for the host and sfv gene trees, which indicated synchronous genetic divergence in both data sets. by using the molecular clock, it was observed that the substitution rates for the host and sfv genes were very similar. the substitution rates for host coii gene and the sfv gene were found out to be (1.16±0.35)×10−8 and (1.7±0.45)×10−8 respectively. this is the slowest rate of substitution observed for rna viruses and is closer to that of dna viruses and endogenous retroviruses. this rate is quite different from that of exogenous rna viruses such as hiv and influenza a virus (10−3 to 10−4 substitutions per site per year). prevalence researchers in cameroon, the democratic republic of the congo, france, gabon, germany, japan, rwanda, the united kingdom, and the united states have found that simian foamy virus is widespread among wild chimpanzees throughout equatorial africa. humans exposed to wild primates, including chimpanzees, can acquire sfv infections. since the long-term consequences of these cross-species infections are not known, it is important to determine to what extent wild primates are infected with simian foamy viruses. in this study, researchers tested this question for wild chimpanzees by using novel noninvasive methods. analyzing over 700 fecal samples from 25 chimpanzee communities across sub-saharan africa, the researchers obtained viral sequences from a large proportion of these communities, showing a range of infection rates from 44% to 100%. major disease outbreaks have originated from cross-species transmission of infectious agents between primates and humans, making it important to learn more about how these cross-species transfers occur. the high sfv infection rates of chimpanzees provide an opportunity to monitor where humans are exposed to these viruses. identifying the locations may help determine where the highest rates of human–chimpanzee interactions occur. this may predict what other pathogens may jump the species barrier next.