Concealed ovulation

Pawlowski, B. (1999) Loss of oestrus and concealed ovulation in human evolution - the case against the sexual-selection hypothesis. Curr. Anthropol. 40, 257-275. 

Sillen-Tullberg, B. and Mailer, A. P. (1993). The relationship between concealed ovulation and mating systems in anthropoid primates a phylogenetic analysis. American Naturalist 141, 1-25. 

Alexander, R. D. Noonan, K. M. 1979. Concealment of ovulation, parental care, and human social evolution. In Evolutionary biology and human social organization (Ed. by N. A. Chagnon W. G. Irons), pp. 436-453. Duxbury North Scituate. 

The primary problem in studying human reproduction is that many aspects of the reproductive process occur without the knowledge of either the woman or her physician. Ovulation, fertilization, and implantation all occur as concealed events. Reproductive biologists and epidemiologists, however, have recently developed new and incisive tools to associate exposures to reproductive health. While it will be years... 

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