WASHINGTON — The House panel investigating the origins of the coronavirus pandemic opened its first public hearing on Wednesday with Republicans and their witnesses making an aggressive case that the virus may have been the result of a laboratory leak — a notion that has become the subject of intense political and scientific debate.
“There is no smoking gun proving a lab origin hypothesis, but the growing body of circumstantial evidence suggests a gun that, at the very least, is warm to the touch,” said Jamie Metzl, a senior fellow at the Atlantic Council and a former State Department official.
Dr. Metzl was one of three witnesses invited by Republicans. The others were Dr. Robert R. Redfield, who served as the director of the Centers for Disease Control and Prevention under President Donald J. Trump, and Nicholas Wade, who was the science editor of The New York Times in the 1990s and left the news organization at the end of 2011.
The three have previously said the virus may have accidentally escaped from a laboratory. But they all said on Wednesday that the question of how the virus originated remained an open one, and that it was important to settle the question.
Dr. Paul G. Auwaerter, the clinical director of the infectious diseases division at the Johns Hopkins University School of Medicine, testified at the invitation of Democrats.
Some proponents of the laboratory leak hypothesis have suggested that it was a biological weapon intentionally engineered by China. But Dr. Redfield, a virologist, said he had concluded that the virus was a result of an accident, and that his view was based “primarily on the biology of the virus itself,” including the fact that it was highly infectious, spawning the rapid evolution of new variants.
Scientists have said that ability could very well have evolved through a natural spillover from an animal. They have cited, among other things, coronaviruses found in bats in 2020 that carry a molecular hook on their surface that is very similar to a feature on the virus that causes Covid-19. That hook allows the viruses to latch onto human cells.
Dr. Redfield also called for a moratorium on “gain of function” research, which involves tinkering with the genes of viruses in a way that could make them more infectious. Many scientists argue that such research is necessary to help develop vaccines and other medical countermeasures that could be used in a pandemic.
“I disagree with that assessment,” Dr. Redfield said.