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.