And shall not Babel be with Lebab?
Sex in reptiles and fish is determined after conception, during embryogenesis, according to ambient environmental temperature. In contrast, in mammals and birds, sex is determined at conception.
In mammals, male births invariably occur slightly in excess […] with approximately 3% more males born than females. The reason for this discrepancy is uncertain as testicles produce equal numbers of X-bearing and Y-bearing spermatozoa. […]
We have shown that M/F varies in geographical space, exhibiting a latitude gradient, and that this gradient is different in Europe and North America, with more males born towards the south of Europe, compared with the North American continent where more males are born towards the north of the continent.
Other studies have also shown that M/F may vary with time. Several authors have shown that M/F has declined over the second half of the 20th century in various industrialised countries. These include Denmark, the United Kingdom, the Netherlands, Germany, Canada, the United States of America, and Finland. In contrast, M/F has been noted to have risen in Ireland over the same period. A non-significant rise in M/F has also been noted in Australia and Japan.
{ J Epidemiol Community Health | Continue reading }
A wide variety of factors have been shown to influence the male to female ratio at birth, which invariably displays a male excess. […] It will be shown that stress, including stress related to political events, influences this ratio.
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