evidence: Nature examines arguments that the coronavirus SARS-CoV-2 escaped from a lab in China, and the science behind them. [...] Debate over the idea that the SARS-CoV-2 coronavirus emerged from a laboratory has escalated over the past few weeks, coinciding with the annual World Health Assembly, at which the World Health Organization (WHO) and officials from nearly 200 countries discussed the COVID-19 pandemic. After last year’s assembly, the WHO agreed to sponsor the first phase of an investigation into the pandemic’s origins, which took place in China in early 2021.