 Thomas is notable for a number of scientific publications in the fields of human demographic and evolutionary history inference, molecular phylogenetics of extinct species using ancient DNA, Cultural evolutionary modelling, and molecular biology.In 1994 Thomas was one of the first people to read the DNA sequence of the extinct woolly mammoth and in 1998 he coauthored a paper providing genetic support to the claim of recent patrilineal common ancestry among the Jewish priestly caste known as Kohanim (singular "Kohen", "Cohen", or Kohane).Between 2000 and 2003 Thomas coauthored several other papers on the origins of various Jewish and Judaic groups, including the Lemba, otherwise known as the "Black Jews of Southern Africa".