World Population 
excess white males will end up by marrying negresses, because 
there aren’t enough white women? 
Parkes: I doubt whether the question of polyandry or 
polygyny influences the sex-ratio of the offspring in any 
scientifically detectable way. 
Coon: Not even when it involves marrying younger wives? 
Parkes: That might be an indirect effect. 
Haldane: My colleague S. K. Roy finds among goats a very 
significant excess of females among single births and males 
among twin births. This appears to me to be a novel observa- 
tion, but perhaps Professor Parkes will tell me that it has been 
known for fifty years. 
Parkes: Not by me, sir! The only explanation of this 
observation that I can think of is that the higher sex-ratio in 
identical twins might result from a greater probability of 
splitting in the case of a male blastocyst. 
Haldane: There is no significant excess of like-sexed twin 
pairs suggesting monozygosis. 
Parkes: ‘Then that disposes of the only explanation I have 
to offer. 
Lederberg: Dr. Parkes, would you elaborate on the techni- 
calities of the separation of the X and Y spermatozoa by 
physicochemical means? I know about Gordon’s and Schréders’ 
earlier work on separation of male and female sperm by electro- 
phoresis and I wondered whether their claims had been 
substantiated. 
Parkes: I think someone in England has obtained the 
separation of rabbit sperm into two distinct groups, but without 
a biological test. In general, efforts to repeat these experiments 
have not been successful—possibly because electrophoresis is a 
very complicated procedure, so that it is difficult to reproduce 
an experiment exactly. However, Lindahl in Sweden, using 
a different separation method, namely, differential centri- 
fugation, claimed to have produced a fraction of bull sperm 
which, on insemination, resulted in the birth of eleven consec- 
utive bull calves. That was very promising, but so far as I 
know, Lindahl has not done any large-scale studies. ‘To my 
Lie 
