In search for the driving force that shapes the evolution of the HPeVs, we looked at the ratio of non-synonymous-tosynonymous substitutions (the dN/dS ratio) [24] . For most codons in the VP1 region the ratio is < 0.1 (Figure 2 ). We noticed a few sites that tend to escape from purifying selection displaying dN/dS values > 0.3 (position Q61, A119, G203), or even > 1.0 (position N202 of our alignment, see additional file 7), however with statistically poor support (see additional file 6, Log-likelihood and parameter estimates for PAML analysis).