The Bennet sisters in Jane Austen's "Pride and prejudice" are Five daughters and no son: for parents, happiness and a burden at the same time. In the end of the 18th century. Century based you need to advise your daughters to painstakingly marry, in order to achieve the former goal in life – protection through marriage. The result of a new study would have the Bennet family, perhaps, peace of mind: Whether and how many boys or girls are born in a family is not hereditary, but a pure coincidence. The sisters thus had a Chance of male offspring.

That the sex ratio is not genetically predisposed, a report by researchers Brendan Zietsch, from the University of Queensland in the journal "Proceedings of the Royal Society B". "Virtually every other human characteristic, has been studied, is to a certain degree, hereditary," says Zietsch. But it is "happy coincidence" if a woman gives birth to many boys, or girls.

siblings should produce similar sex ratios

About the influence of factors on the sex of the offspring evolution discuss biologists for a long time. So far, the Study of the influence of parental genetics on the birth rate was uncertain. "I knew that we must meet the Problem with a sledgehammer on the head, in order to solve it," says Zietsch.

The solution came from Sweden. The authorities in the Scandinavian country provided the scientists with data of the entire Swedish-born population that came from 1932 to the world. In this way, their study included about 3.5 million parents and more than 4.7 million descendants. The scientists wanted to find out whether the descendants of the siblings, the Cousins of the first degree, were tending to the same sex.

This was not substantiated and was, even then, not so, as the Team was looking for, only first-born children. Zietsch stated the conclusion thus: a sibling genetically, were similar. "If the sex ratio of the offspring is influenced by heritable – i.e. genetic differences, it is recommended that siblings, therefore, have similar sex ratios to produce." The left of the results, however, are not derived.

and More girls because of climate

With his study, wants to have upsetting the team of researchers, a number of old theories. One of them is the Fisher principle. This evolutionary model from the year 1930 indicates that the sex ratio in populations is maintained by natural Selection in an upright position. If the gender ratio is skewed in one direction, to be children of persons with the predisposition to have offspring of the rarer sex are more attractive. Compensate for the imbalance by itself to bring forth more children. For Brendan Zietsch of this approach is the respect of the people, so it is no longer tenable.

But if it's not in the genes, why a lot of girls and boys to be born then, in many countries different? So 51,22 percent of the newborns were in 2019 in the Switzerland male. Zietsch calls to reconsider the existing theories in order to understand the variability of gender relations across national borders better. Kristen Navara of the University of Georgia in Athens, delivered in 2009 an approach.

In a in the "Biology Letters" published study makes climatic influences responsible for the birth circumstances develop. To this end, the biologist examined the Numbers of live births from 202 countries from 1997 to 2006. Here, differences arose In Africa, it was among the newborns of more girls (49.3 percent) than in Europe and Asia (48.6 per cent). With increasing latitude the proportion of male offspring increased, according to the research. The even had as Navara African and Asian countries took to artificial influences, such as birth, exclude control.

Overall survival of more male than female
embryos in the pregnancy.

similar results were arrived at Shige Song, from the New York City University. He found that girls are more often born when the conditions in your environment are worse. For this purpose, unfavorable weather, crises, wars, or famines belong to. To do this, the researchers analyzed the births during the great famine in China from 1959 to 1961. If it went well, came more girls to the world.

He detected an abrupt decrease of the sex ratio at birth between April 1960, over a year after the beginning of the famine, and October 1963, approximately two years after the end of the famine. The proportion of male births declined in this period, from 52.7 percent to 51.0 percent. These results support the Hypothesis that mothers give birth in a poor condition more daughters than usual.

the anthropologist Ruth Mace also reported in 2003 that, in Ethiopia, in difficult times, fewer boys were born. Weaker women were, according to their investigations, more likely to have girls, the physically more robust of the women's sons rather. The diet of the mother plays a role for the sex of the offspring is also demonstrated by a study in the journal "Proceedings of the Royal Society B". Thus, women, who at the time of conception is very energy - and sugar-rich feed, more boys.

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A possible explanation for the slight imbalance in the gender ratio of newborns, researchers described in Steven Hecht Orzack, of the University of Cambridge 2015 in the journal PNAS. They evaluated the pregnancy histories of thousands of Americans inside. The investigations revealed that at the start, the sex ratio is equal. Only in the course of the pregnancy would change the ratio through Disposals. Overall, more male embryos survived the pregnancy. The result is that the birth rate of the round will be more in favour of the boys.

But even social factors may have an influence on the sex ratio. A corresponding effect William Stansfield and Matthew Carlton in 2007 in "Human Biology discovered". They found that families with only two children a boy and a girl. This division occurred more frequently than expected. However, families with more children were more likely to have an imbalance towards boys or girls. This seems to be due to the fact that parents have so many children, until you have achieved the desired family composition.

Created: 01.03.2020, 22:56 PM