© 1972 by The Society for Integrative and Comparative Biology
Mammalian Conception, Sev Differentiation, and Hermaphroditism as Viewed in Historical Perspective
Biology Department, University of Chicago, and Laboratory for Cell Biology and Histology Unversity of Leiden, The Netherlands
This paper surveys in broad perspective some of the steps in the development of theones of mammalian sex differentiation from antiquity to the present. The questions of why and how males and females differentnte and why there are intersexes have been answered by conjectures, speculations, and theones. In antiquity, when the existence of mimimhan egg and sperm wasunknown sex determination was con]ec tuicd to depend upon such factors as which testis contiibuted the semen or which sideof the uterus received it. These fanciful notions peisisted until the middle of the 18th centuiy. Discovery of mammalian sperm in the same century and the ovum in the 10th centuiy led to obseivations of fertilization. With advances in genetics andthe identification ot sex chromosomes, the 20th century was prepared to construct theories foi normal sev differentiation and inteisexuality based on experimental observation. The bovine freemartin—a natural experiment—prompted the hounonal theory leseaich on frogs led to a coittco medullaiy inductor theory, cellular cmmerism in fteemaitin and co tvun was the basis for a cellular theory. Of these, the hormonal theory in particular, provided some verifiable speculations. However, there is no completely acceptable theory and new lines of research are badly needed