Control of Reproduction in Mammals 
GREGORY PINCUS 
recognized by demographers, economists and sociologists 
and with it the need to develop new methods of fertility 
control!, Methods in common use in Western countries have 
been found to be impracticable or unacceptable in many areas 
of the world. Furthermore, the use of what are principally 
barriers to sperm access to, or movement in, the female repro- 
ductive tract is, even under controlled conditions, accompanied 
by some risk of conception (see Table III below), and more 
*‘fool-proof’’? methods of contraception are therefore desirable. 
When we consider the delicately balanced set of sequential 
processes involved in mammalian reproduction, it is clear that 
there are many possibilities for control by immunological, 
hormonal or other means of manipulation. I have discussed a 
number of these in detail in a forthcoming book on The Control 
of Fertility2. As the result of research which Dr. Chang and I 
initiated with animal experimental work some ten years ago, 
a highly effective method of oral contracepton has been devel- 
oped which is now in increasingly wide use. It is based upon 
our knowledge of the processes which effect the liberation of the 
mammalian egg (the ovum) in the process of ovulation. 
The development of the mammalian egg begins with the 
formation of the germ cells in the embryonic gonad. According 
to the best evidence at present available, the ovary at birth 
contains all the odcytes (primitive ova) destined to last for the 
female’s reproductive life. The slow maturation of the ovaries 
before puberty involves chiefly the development of the follicles 
surrounding the egg, until at puberty ovulation is initiated: an 
egg is released by rupture of a ripe follicle. Thereafter ovulation 
TT magnitude of the population explosion has been 
7 
