Biologists in the 1960s witnessed a period of intense intra-disciplinary negotiations, especially the positioning of organismic biologists relative to molecular biologists. The perceived valorization of the physical sciences by "molecular" biologists became a catalyst creating a unified front of "organismic" biology that incorporated not just evolutionary biologists, but also students of animal behavior, ecology, systematics, botany——in short, almost any biological community that predominantly conducted their research in the field or museum and whose practitioners felt the pinch of the prestige and funding accruing to molecular biologists and biochemists. Ernst Mayr, Theodosius Dobzhansky, and George Gaylord Simpson took leading roles in defending alternatives to what they categorized as the mechanistic approach of chemistry and physics applied to living systems——the "equally wonderful field of organismic biology." Thus, it was through increasingly tense relations with molecular biology that organismic biologists cohered into a distinct community, with their own philosophical grounding, institutional security, and historical identity. Because this identity was based in large part on a fundamental rejection of the physical sciences as a desirable model within biology, organismic biologists succeeded in protecting the future of their field by emphasizing the deep divisions that ran through the biological sciences as a whole.

This paper explores the research and administrative efforts of Ernest Brown Babcock, head of the Division of Genetics in the College of Agriculture at the University of California, Berkeley, the first academic unit so named in the United States. It explores the rationale for his choice of "model organism," the development——and transformation——of his ambitious genetics research program centering on the weedy plant genus named Crepis (commonly known as the hawkbeard), along with examining in detail the historical development of the understanding of genetic mechanisms of evolutionary change in plants leading to the period of the evolutionary synthesis. Chosen initially as the plant counterpart of Thomas Hunt Morgan's Drosophila melanogaster , the genus Crepis instead came to serve as the counterpart of Theodosius Dobzhansky's Drosophila pseudoobscura , leading the way in plant evolutionary genetics, and eventually providing the first comprehensive systematic treatise of any genus that was part of the movement known as biosystematics, or the "new" systematics. The paper also suggests a historical rethinking of the application of the terms model organism, research program, and experimental system in the history of biology.