[1] His writings focus especially on evolutionary biology beyond the classical neo-Darwinian framework, and emphasize the fundamental importance of symbiosis and horizontal gene transfer in heredity and evolution.

[3] He held the Canada Research Chair (tier 1) in the History of the Biological Sciences at l’Université du Québec à Montréal from 2001 to 2003[4] before returning to York University where he has been a professor since 1992.

He developed this line of historical research beyond classical neoDarwinian biology further in his book on the history of microbial phylogenetics, The New Foundations of Evolution: On the Tree of Life (2009).

In 2021, Sapp published Genes, Germs and Medicine, an exploration of the development of modern biomedical science in the United States through the life of Joshua Lederberg, an influential scientist.

Lederberg his collaborators founded the field of bacterial genetics, and age 33, was the second youngest person in history to win the Nobel Prize.