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. within a few weeks, it became one of the most cited scientific papers in history, meaning that other scientists were reading and using it.