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Encyclopedia of Animal Cognition and Behavior, 2019
Anna Szala, Todd K. Shackelford
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Anna Szala, Todd K. Shackelford
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Sex differences, sex ratios and sex roles
Proceedings of the Royal Society of London. Series B: Biological Sciences, 1994Sexual selection theory predicts that sex roles will be determined by the operational sex ratio (OSR), the sex ratio among individuals searching for mates at any given time. There are two predictions: (i) the sex which is in 'excess' will be the more competitive sex with respect to access to mates; and (ii) the sex of which there is a 'shortage' will ...
I P, Owens, D B, Thompson
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Group sex ratio and sex reversal
Journal of Theoretical Biology, 1980Abstract In hermaphroditic fishes, the initiation of sex reversal by male removal explains the replacement of lost males but does not explain how the number of males in a group may increase. Since numerous species apparently cannot produce primary males, a second means of initiating sex reversal must exist.
Douglas Y. Shapiro, Roger Lubbock
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Sex ratio under conditional sex expression
Journal of Theoretical Biology, 1988We present a model to show that, when sex depends on environment rather than genotype, the sex expressed under relatively unfavorable conditions will be more abundant. This result refers to numbers of males and females in the population. By contrast, no clear prediction can be made about the allocation of resources to the two sexes.
S A, Frank, I R, Swingland
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jpme, 1995
Since the introduction of different ovulation induction regimens the incidence of triplet pregnancies increased from a spontaneous rate of about 1:10,000 to the frequency of nearly 1:1000. Sex ratio of trigemini and male/female proportion of the three newborns within the same triplet set is the amazing issue that we attempted to elucidate in the ...
N, Mordel +5 more
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Since the introduction of different ovulation induction regimens the incidence of triplet pregnancies increased from a spontaneous rate of about 1:10,000 to the frequency of nearly 1:1000. Sex ratio of trigemini and male/female proportion of the three newborns within the same triplet set is the amazing issue that we attempted to elucidate in the ...
N, Mordel +5 more
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Transactions. Edinburgh Obstetrical Society
sexes among newly-born infants?is very nearly equality, being about 104 males per 100 females. That this is so is provocative of thought, for from the point of view of the sex physiologist this equality is so very unnecessary.
F. Crew
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sexes among newly-born infants?is very nearly equality, being about 104 males per 100 females. That this is so is provocative of thought, for from the point of view of the sex physiologist this equality is so very unnecessary.
F. Crew
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Sex Ratio And Placenta Praevia
Acta Obstetricia et Gynecologica Scandinavica, 1989In the authors' Department, 144 cases of placenta praevia were treated in the course of 15 years. This number amounted to 0.54% of all births. The sex ratio of fetuses inassociated with this complication was 166.6, which exceeds that of all neonates during the same period of time.
A A, Jakobovits, L, Zubek
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Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring
Science, 1973R. Trivers, D. Willard
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