What is George Church's first scientific discovery or contribution to science?

George McDonald Church (born 28 August 1954) is an American geneticist, molecular engineer, and chemist. As of 2015, he is also known as Robert Winthrop Professor of Genetics at Harvard Medical School and Professor of Health Sciences and Technology at Harvard and MIT, and was a founding member of the Wyss Institute for Biologically Inspired Engineering at Harvard. As of March 2017, Church serves as a member of the Bulletin of the Atomic Scientists' Board of Sponsors.