Sarbecoviruses have crossed into humans twice in the last decade, leading to the deadly SARS-CoV-1 outbreak in 2002-04 and the current COVID-19 pandemic, caused by the SARS-CoV-2 virus. A new Oxford University Study, published today, shows that the most recent common ancestor of these viruses existed more than 21,000 years ago, nearly 30 times older than previous estimates.
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.
‘We developed a new method that can recover the age of viruses over longer timescales and correct for a kind of ‘evolutionary relativity’, where the apparent rate of evolution depends on the timescale of measurement. 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.