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64 Paul Kammerer had amassed good zoological evidence for the inheritance of acquired characteristics. This was one reason why he was at the center of so much controversy. But new cellular evidence on the mechanisms of heredity— the discovery of chromosomes and the stability and reappearance of attributes in hereditary transmission—raised important scientific questions that required a different kind of answer. The validity of the idea no longer depended on zoological demonstrations like the ones that Kammerer had developed. Instead, evidence in physiology and cell biology was necessary to bring the concept into modern discussions framed by chromosomes and the process of meiosis. Semon’s theories had focused the issue, but in a language that did not produce meaningful scientific tests. Indeed, until Przibram’s 1911 call to examine the gonad, most appeals to physiology were vague and speculative. After Przibram hired Steinach and evidence on the interstitial cell question had begun to favor a secretory function, Kammerer could avail himself of a valuable new approach. All of Steinach’s research promoted the idea that the gonad was a double gland––one structure that functioned as two separate glands, one serving reproduction and the other sexuality proper (see Chapter 2). In 1915, many scientists still treated the two functions as one and vested them in eggs and sperm. But Steinach’s rise was based on his confirmation of two glands with quite different functions, and by 1919, Kammerer had become a vocal supporter of Steinach’s research on the interstitial cells and flexibility in sexual development. He began to argue that the double gonad could also provide the cellular mechanism needed to explain how the inheritance of acquired characteristics occurred. The interstitial cells were the key to somatic induction, and collaboration with Steinach would yield the needed evidence. But Kammerer’s motives were also social. After the war ended, he became more concerned about 4 Sex, Race, and Heat Rats Somatic Induction and the Double Gonad SEx, RACE, AND HEAT RATS 65 the growing rigidity of the race concept in science. He believed that if research on the mammalian double gonad could solve the problem of somatic induction , it could help explain racial differences in human sexuality flexibly without recourse to rigid racial boundaries. Steinach and Kammerer’s experiments focused on rat sexual development. But they extended their collaboration well beyond the animal data to address the sex differences described among human populations. Anthropologists had distinguished the so-called “civilized” peoples of Europe, then called Kulturvölker, from what many regarded as the “primitive” peoples of Africa, native America, and the Polynesian Islands, whom they called Naturvölker. The terminology reflects their assumption that civilization, “culture,” and the proper sexual restraint and specialization they entailed had evolved only in European “races.” “Races” of natural people were assumed to be more like animals. Kammerer disagreed; his goal was to account for differences in the presumed racial sexuality of humans by rejecting the rigidity of the race concept, a concept that by1920 was anchored in Weismannist genetics.1 Instead, he and Steinach would rely on inferences from their rat tests to show that racial differences in human sexuality were the result of climate acting on heredity in a way mediated by somatic induction. The Endocrine Hypothesis of Somatic Induction Paul Kammerer’s interests in sexuality and physiology were long-standing. In the program of study that he proposed in his 1908 application for the Habilitation , Kammerer listed the comparative physiology of reproduction and the physiology of heredity among the several fields that he would master.2 In 1912, he compiled that information into a comprehensive review of the question of sex differences that was published in Emil Abderhalden’s influential Fortschritte der naturwissenschaftliche Forschung (Progress in scientific research).3 The review was impressively comprehensive; it treated the science of reproduction as a far-reaching window into the problems of species and racial development and the nature of heredity. Kammerer dealt with confusions in the common terminology used to describe sex differences (primary, secondary, and tertiary), with sex ratios, with Morgan and Edmund Wilson’s heterochromosome theory , and with Richard Hertwig’s ideas on the relationship between cytoplasm and germ-plasm—hinting that chromosomes could incorporate aspects of the outer environment. He reviewed several ideas about the origin of sex differences , and supported the new interstitial cell hypothesis of Ancel, Bouin, and others. Steinach was mentioned, but only as a minor figure. Kammerer placed greater emphasis on the work of Tandler, Hertwig...

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