In July 2020 he became Director of Enrollment Management and Student Success at Touro University California's College of Osteopathic Medicine, where he has served professionally for 25 years.

He undertook graduate work in biological anthropology under the late Francis Clark Howell at the University of California at Berkeley in 1986, where he developed an interest in South American monkeys.

[2] Hartwig turned to comparative cranial anatomy for his dissertation research, conducted at the Field Museum of Natural History in Chicago.

He had the opportunity there to work closely with John Fleagle,[4] whose broad vision of primate evolution has been a significant influence in Hartwig’s writings.

In 1997 what is now the Touro University College of Osteopathic Medicine opened in San Francisco and Hartwig joined the founding faculty as an anatomist.

Together with eminent Brazilian paleontologist Castor Cartelle he published and named the first evidence of extinct "mega-monkeys", two species that were more than twice the size of any living South American monkey.