After an internship in
New Jersey, he trained in pathology at university hospitals affiliated with
Harvard Medical School in
Boston. In 1955, he became pathologist of the Boston Lying-in Hospital, now part of the
Brigham and Women's Hospital, and there developed his interest in the placenta and reproductive problems. From 1960 to 1970 he was the chairman of the department of pathology at
Dartmouth Medical School in
Hanover, New Hampshire, and pursued his interests in placental pathology and comparative reproductive pathology. There, he developed a passion for comparative cytogenetics, discovering the reason for the
sterility of
mules and investigating
twinning in
armadillos and
marmosets. In 1970, Benirschke moved west to participate in the development of a new medical school of the
University of California, San Diego (UCSD). He established a genetics laboratory and ran the
autopsy service at UCSD. He also chaired the department of pathology for two years. In 1976, Benirschke persuaded the Board of Trustees of the
San Diego Zoo to establish a formal research department. Benirschke led this new research department, which was named the Center for the Reproduction of Endangered Species, until 1987 when he became a member of the Zoo's Board of Trustees. He set up a laboratory at the Zoo to study the
chromosomes of
mammals, particularly aspects relating to reproduction and evolution. In collaboration with
T.C. Hsu, he published an
Atlas of Mammalian Chromosomes which presented the
karyotypes of 400 different species of mammals. He established at the Zoo a collection of frozen cells and reproductive material from dozens of highly endangered species that became famous as the first "
Frozen Zoo". In the 1970s when he began this collection, there was no technology available to make use of it, but he quoted
Daniel Boorstin: "You must collect things for reasons you don't yet understand." The Frozen Zoo eventually became a priceless genetic resource. Throughout his career, he moved freely back and forth between human medicine and animal medicine. This inspired the title
One Medicine given to a
Festschrift written by 50 of his colleagues to honor his 60th birthday. In the introduction, O. A. Ryder and M. L. Byrd state, "The acknowledgment that the underlying mechanisms of cellular function and organismal development are highly similar among animals provides the impetus for the title of this volume,
One Medicine. It is a tribute to Prof. Kurt Benirschke from his students and colleagues. As such, we attempt to recognize the breadth and depth of his thinking and to acknowledge the significant role he has played in aspects of human medicine, veterinary medicine, and wildlife conservation." In 1994, he was elected a fellow of the
American Academy of Arts and Sciences. The same year, he retired from the faculty at UCSD. From 1997-2000 he was president of the Zoo's Board of Trustees and looked after the "Proyecto Tagua" in
Paraguay, a breeding facility of the newly discovered species of
peccary. His text (with Peter Kaufmann) on
Human Placental Pathology is the standard text on the subject. In 2008 he was one of the founders of the
Center for Academic Research and Training in Anthropogeny (CARTA), an interdisciplinary research group based at UCSD and devoted to the study of human origins. Benirschke was a member of many societies and authored 30 books and 510 scientific publications. He was described as a "visionary" and a "Renaissance physician". ==Personal life==