Variations in boy girl baby ratios.

In Nature 2007, vol 450 p 765 there is a fascinating summary of two papers describing variations in male female ratios in babies
. Biol. Lett. doi:10.1O98/rsbl.2007.0482 (2007);
Proc. R. Soc. B doi:10.1098/rspb.2007.1401 (2007)
Evolutionary theory suggests that sexual creatures increase the number of descendants if they have more sons than daughters when conditions are optimal and more daughters than sons in less ideal circumstances. How this happens is not clear.
It may also be that after wars, more male babies are born than female.
Samuli Helle, of the University of Turku in Finland, and his colleagues report a correlation between the annual mean temperature in northern Finland and the sex ratio of newborns in three populations of indigenous Sami people for the years 1745-1890. The team compared demographic data from the parish registers of Lutheran churches with a climatic record reconstructed from tree rings and an index of the North Atlantic Oscillation. Warmer years brought an increased proportion of boys, in keeping with theory.
Elissa Cameron, of the University of Pretoria in South Africa, and her colleagues raised the proportion of daughters in mouse litters by lowering the blood glucose levels of females during conception. The researchers added dexamethasone, a steroid that blocks glucose uptake into the blood, to the drinking water of female mice for three days while the animals had access to a mate. Only 41,9% of the litters of dexamethasone-treated mice were male, compared with 53.5% in control litters.
This suggests a fascinating research project. The effect of diet on the male female ratio of offspring. Easy in mice. Firstly a nutritionally adequate , an adequate and insufficient diet.
Pregnancy can often happen if the girl is drunk so study alcohol ( beer, white and re wine )
Then the vast array of food and herb aphrodisiacs, which include oysters and chocolate.

Martin Eastwood
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