Despite having a very rapid rate of evolution over short timescales, to survive, viruses must remain highly adapted to their hosts - this imposes severe restrictions on their freedom to accumulate mutations without reducing their fitness. This causes the apparent rate of evolution of viruses to slow down over time. The new research, for the first time, successfully recreates the patterns of this observed rate decay in viruses. Our estimate based on viral sequence data, of more than 21,000 years ago, is in remarkable concordance with a recent analysis on human genomic dataset that suggests infection with an ancient coronavirus around the same time.’ Said Mahan Ghafari, from Oxford University. HCV may thus have spread worldwide as an intrinsic part of the “Out-of-Africa” migration of modern humans around 150,000 years ago.
