In "An Introduction to Genetics" by David J. Merrell, copyright 1975 by W.W. Norton + Co., p. 742, in the Chapter "Genetic Counseling and Eugenics," the author states: "... 50% of the women produce 85% of all children born in the United States."
The author provides an Additional Reading list, but I'm not a geneticist, nor do I have access to much of the listed material. With that in mind, 1) where can one find the statistic mentioned above? and 2) has this number changed over time?
OP EDIT: In response to comment (a few examples from Reading List of 30 items):
Davis, 1970, Prospects for Genetic Intervention in Man, Science, 170 279-1283
Dubos,1965, Man Adapting, Yale Univ. Press
Dunn, 1962, Cross Currents in the History of Human Genetics, Amer. J. Human Genet, 14: 1-13
Ehrlich, 1968, The Population Bomb, Ballantine NY
Lynch, 1969, Dynamic Genetic Counseling for Clinicians, C. C. Thomas, Springfield, Mass.
Petersen, 1969, Population, 2nd Ed. Macmillan
1969, WHO Expert Comm. on Human Genetics, "Genetic Counselling(sic), Tech Rept 416, pp. 1-23
I know I can find stats like average ages, etc from the Statistical Abstract of the United States, but where do geneticists find items like the one cited in the Merrell book?