on march 17, 2020, scientists from columbia university and other places published a paper in "nature medicine" showing that sars-cov-2 was almost surely not made by humans in a laboratory. they did this by comparing the genomes of different viruses to each other. the scientists saw that sars-cov-2 did not match any of the viral backbones that already exist for virologists to use. the paper in "nature medicine" soon became one of the most cited scientific papers of all time.