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Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring
Robert L. Trivers and Dan E. Willard
New Series, Vol. 179, No. 4068 (Jan. 5, 1973), pp. 90-92
Published by: American Association for the Advancement of Science
Stable URL: http://www.jstor.org/stable/1734960
Page Count: 3
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Theory and data suggest that a male in good condition at the end of the period of parental investment is expected to outreproduce a sister in similar condition, while she is expected to outreproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. Data from mammals support the model: As maternal condition declines, the adult female tends to produce a lower ratio of males to females.
Science © 1973 American Association for the Advancement of Science