Hermanussen studied medicine and worked as a pediatrician at the University of Kiel from 1982 until 1989.
Intern University Hamburg. Resident Children's Hospital, Kiel, Germany, staff pediatrician Germany, Germany, 1982-1985, 86-89. Research fellow University California, San Diego, 1985-1986.
Private practice Gettorf, Germany, since 1989. Lecturer University Kiel, 1990. Independent researcher in association with University Madrid, University Heidelberg, Germany, University Leipzig, Germany.
Coordinator research on short-term growth University Kiel, 1985-1989, private research, Germany and Spain, since 1989.
From 2003 to 2011 he was a member of the scientific board of the German society for Anthropology and chief editor of ”Anthropologischer Anzeiger”.
Married Beate Lohse-Hermanussen, December 19, 1982. Children: Johanna, Christian, Claus-Hinrich, Elisabeth, Georg-Willem.