Erroneous theories of sex determination

SUMMARY Throughout the major part of history, theories of sex determination had to be formulated in the absence of knowledge of ova and spermatozoa. The most persistent theory postulated that males are associated with the right parental side and females with the left side. At the end of the 19th century, sex was thought to be determined by nutrition. Recent findings regarding bilateral asymmetry in human hermaphrodites and of temperature dependent sex determination in reptiles may restore a small degree of credibility to certain theories predating the discovery of sex chromosomes. Since the discovery of sex chromosomes occurred at the beginning of the 20th century, all ideas before this time fall into the category of 'prescientific'. Pre-scientific ideas are not necessarily wrong, any more than ideas developed during the scientific era are invariably right. In 1912, when H J Muller was a student at Cornell Medical College, he wrote a paper entitled 'Erroneous assumptions regarding genes', which at the time he was unable to publish. This is hardly surprising, for in this paper Muller complained about "certain needless assumptions regarding sex " and criticised the genetic formulae proposed by his teacher, T H Morgan, to explain sex determination in Drosophila. Part of this paper was later included in an article 'Some genetic aspects of sex'.I The present account will confine itself to theories of pre-20th century vintage. By the 19th century the number of theories to explain the determination of sex had been estimated at about 500. In a famous passage by Geddes and Thomson2 we read that: "The number of speculations as to the nature of sex has been well-nigh doubled since Drelincourt, in the last century, brought together two hundred and sixty-two 'groundless hypotheses'. and since Blumenbach quaintly remarked that nothing was more certain than that Drelincourt's own theory formed the two hundred and sixty-third. Subsequent investigators have, of course, long ago added Blumenbach's 'Bildungstrieb ' to the list". Reccived for ptibliitioii 8 Septcmhcr 1984. Acceptc ( for public;tion X ()tohb r 1984