His high school teacher, Robert Meyer, encouraged Hartl to apply for a scholarship, which allowed him to attend University of Wisconsin–Marathon County in Wausau, Wisconsin for two years.
[1][3] Hartl studied Drosophila (a group of fruit flies) and investigated "the mystery of segregation distortion.
He has published work on population genetic theory, tests of selection,[4] evolution of antimicrobial resistance in E. coli[5] and malaria.
[7] As of 2017 research at the Hartl Laboratory at Harvard University focused on evolutionary genomics, molecular evolution, and population genetics.
[10] Hartl is the 2019 recipient of the Thomas Hunt Morgan Medal from the Genetics Society of America (GSA).