منابع مشابه
Anencephalus: a changing sex ratio.
The sex ratio of infants born with certain congenital abnormalities diverges widely from unity. There is evidence that these sex ratios vary from place to place and in different races (Gittlesohn and Milham, 1962; Emanuel, 1972). Stocks (1970) has shown that within 25 countries of largely European stock there is a close positive correlation between the divergence of the sex ratio of congenital ...
متن کاملA note on the sex ratio in anencephalus.
While exploring the association of the sex ratio of stillbirths with cause and duration of gestation, McKeown and Lowe (1951) noted that for anencephalus sex ratio increased with duration of gestation. No explanation was offered for this observation, which is here considered briefly. In Birmingham, during the years 1940-51, 454 stillbirths and 28 infant deaths were attributed to anencephalus (4...
متن کاملSex-ratio evolution in sex changing animals.
Sex allocation theory is often able to make clear predictions about when individuals should facultatively adjust their offspring sex ratio (proportion male) in response to local conditions, but not the consequences for the overall population sex ratio. A notable exception to this is in sex changing organisms, where theory predicts that: (1) organisms should have a sex ratio biased toward the "f...
متن کاملDensity-dependent sex ratio adjustment and the allee effect: a model and a test using a sex-changing fish.
Positive density dependence (i.e., the Allee effect; AE) often has important implications for the dynamics and conservation of populations. Here, we show that density-dependent sex ratio adjustment in response to sexual selection may be a common AE mechanism. Specifically, using an analytical model we show that an AE is expected whenever one sex is more fecund than the other and sex ratio bias ...
متن کاملSex Ratio Elasticity Influences the Selection of Sex Ratio Strategy
There are three sex ratio strategies (SRS) in nature-male-biased sex ratio, female-biased sex ratio and, equal sex ratio. It was R. A. Fisher who first explained why most species in nature display a sex ratio of ½. Consequent SRS theories such as Hamilton's local mate competition (LMC) and Clark's local resource competition (LRC) separately explained the observed deviations from the seemingly u...
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ژورنال
عنوان ژورنال: Journal of Epidemiology & Community Health
سال: 1973
ISSN: 0143-005X
DOI: 10.1136/jech.27.2.81