Cheryl Logan

After 1900, the selective breeding of a few standard animals for research in the life sciences changed the way science was done. Among the pervasive changes was a transformation in scientists' assumptions about relationship between diversity and generality. Examination of the contents of two prominent physiology journals between 1885 and 1900, reveals that scientists used a diverse array of organisms in empirical research. Experimental physiologists gave many reasons for the choice of test animals, some practical and others truly comparative. But, despite strong philosophical differences in the approaches they represented, the view that it was best to incorporate as many species as possible into research on physiological processes was widespread in both periodicals. Authors aimed for generality, but they treated it as a conclusion that would or would not follow from the examination of many species. After 1900, an increasing emphasis on standardization, the growth of the experimental method and the growing industrialization of the life sciences led to a decline in the number of species used in research. In this context, the selective breeding of animals for science facilitated a change in assumptions about the relationship between generality and diversity. As animals were increasingly viewed as things that were assumed to be fundamentally similar, scientific generality became an a priori assumption rather than an empirical conclusion

In 1920, Eugen Steinach and Paul Kammerer reported experiments showing that exposure to high temperatures altered the structure of the gonad and produced hyper-sexuality in "heat rats," presumably as a result of the increased production of sex hormones. Using Steinach's evidence that the gonad is a double gland with distinct sexual and generative functions, they used their findings to explain "racial" differences in the sexuality of indigenous tropical peoples and Europeans. The authors also reported that heat induced anatomical changes in the interstitial cells of the gonad were inherited by the heat rats' descendants. Kammerer used this finding to link endocrinology to his long-standing interest in the inheritance of acquired characteristics. The heat rats supported his hypothesis that the interstitial cells of the double gland were the mechanism of somatic induction in the inheritance of acquired characteristics. The Steinach-Kammerer collaboration, Kammerer's use of Steinach's "puberty gland" to explain somatic induction, and his endocrine analysis of symbiosis reveal Paul Kammerer's late career attempt to integrate endocrinology and genetics with the political ideals of Austrian socialism. With them he developed a bioethics that challenged the growing reliance on race in eugenics and instead promoted cooperation over competition in evolution. I relate his attempt to the controversies surrounding the interstitial cells, to the status of extra-nuclear theories of heredity, and to Kammerer's commitment to Austromarxist social reforms during the interwar period.

In America by the 1930s, albino rats had become a kind of generic standard in research on physiology and behavior that de-emphasized diversity across species. However, prior to about 1915, the early work of many of the pioneer rat researchers in America and in central Europe reflected a strong interest in species differences and a deep regard for diversity. These scientists sought broad, often medical, generality, but their quest for generality using a standard animal did not entail a de-emphasis of organic diversity. They chose white rats as test animals for two primary reasons. First, rats develop very slowly. They therefore made features of physiological, neural and psychological development accessible to the experimental method at a time when its application to the phenomena of development remained controversial. Secondly, rats were thought to have unusually strong sex drives. For this reason they became central to the experimental study of sexuality and, in the work of the reproductive physiologist Eugen Steinach, sexual development. Connections among three research institutes that stressed experimental approaches to the study of brain and development demonstrate the importance of the rat's institutional role. As the emphasis on experimentation in the study of development grew, two of these institutes bred rats to provide uniform materials. Eventually, however, their reasons for selecting rats were lost; and the ready availability of a uniform test animal led to a shift in scientists' presumptions about diversity, as the standard rat became a tool for assuring generality.