Dr. Joel Wertheim is an Associate Professor in the Division of Infectious Diseases and Global Public Health at UCSD School of Medicine. His work focuses on the molecular evolution and phylogenetic of RNA viruses. By using genome data collected from the early cases of the COVID-19 pandemic, combined with molecular clock inference and epidemiological simulation, Dr. Wertheim and his team established how long SARS-CoV-2 could have circulated before the time of the most recent common ancestor of all sequenced SARS-CoV-2 genomes.