102 SECTIONAL ADDRESSES 



and female mortality rates, it is much more likely that sex-limited defects 

 and derangements, expressed either before birth or in senescence, are 

 also heavily concerned. 



Sex differences in chromosome constitution may imply more than a 

 difference in respect of sex-limitation and of sex-linked lethals ; they 

 may mean also a difference in genie balance. Two X-chromosomes 

 together with two sets of autosomes include a gene association different 

 from that which is resident in one X-chromosome and a Y-chromosome 

 plus two sets of autosomes. The work of Gowen (1931) who studied the 

 duration of life in males, females, triploid females and sex-intergrades of 

 Drosophila melanogaster to find that the average length of life was 33*1, 

 28-9, 33 • I and 15 days respectively, can be regarded as providing evidence 

 that differences in chromosome balance is a factor in determining the 

 span of life. It may be that this difference in genie balance between 

 male and female is itself a cause of unequal mortality, though it is difficult 

 to regard the male as being less well balanced genically since he has 

 endured as long a course of selection as has the female and it would be 

 expected that dosage compensation would ensure a proper balance in 

 each sex regardless of differences in dosage ratios. 



There are other differences, metabolic and physiological, which quickly 

 appear in development and which, in turn, give rise to endocrinological 

 differences which, when once established, take charge of further differ- 

 entiation and the maintenance of sexuality in the higher forms. The 

 initial genetic constitution would seem to determine which of two alter- 

 native types of dift'erentiation shall occur — either toward testis formation, 

 or else toward ovary formation — and, with the incoming of the gonad and 

 the rest of the endocrine system, maleness or else femaleness becomes 

 finally and firmly established. These two states or conditions are to be 

 distinguished by sustained differences in oxidation rate. 



It will be remembered that Geddes and Thomson (1889), having 

 looked widely upon living things, were driven to the conclusion that 

 males are predominantly catabolic, females anabolic, that the deep 

 constitutional difference between the male and the female organism which 

 makes one a sperm-producer and the other an egg-producer was due to 

 an initial difference in the balance of chemical agencies. This hypothesis 

 has been much refined and elaborated by Riddle (193 1) who assumes 

 that the genes exercise their influence on developing sexuality by establish- 

 ing higher or lower oxidation rates. He points out that if sex differences 

 rest primarily on prolonged and sustained differences in the rate of 

 cellular oxidation during the earliest phases of development, this difference 

 should often be well expressed in adult stages as well and should manifest 

 itself in adequate measurements of metabolic rate and in various states or 

 conditions of the blood and tissues which restrict, indicate or accompany 

 metabolic rate. Adequate measurements of basal metabolism of the 

 sexes have been made in the young human (Benedict and Talbot, 1921), 

 adult human (Benedict and Emmes, 1914, and also Gephart and du Bois, 

 (191 6), in the adult fowl (Mitchell, Card and Haines, 1927), the rat 

 (Benedict and MacLeod, 1929) and in the ring dove (Riddle, Christman 

 and Benedict, 1930). In every case the higher metabolism, from 3 to 



