Is a child’s sex really a coincidence? This is the question raised by a study conducted by researchers at Harvard’s TH Chan School of Public Health. It suggests that there could in fact be a biological bias, even if some scientists’ counterparts have some reservations about these results, tempers an article from IFL Science. In the collective unconscious, the probability of giving birth to a girl or a boy is a matter of chance, a one in two chance like when you flip a coin.
This idea is based on the principle of meiosis, a type of cell division in which sperm containing X and Y chromosomes are produced in equal quantities. However, this theory does not completely reflect reality: the determination of the sex of the child is not decided solely from the chromosomes.
The study is based on a lengthy analysis of data from 58,007 American women. The results showed that there were many more families with children of the same sex, so that the chances were actually half. How then can we explain these households composed only of little girls or little boys?
One of the first explanations that researchers give for this imbalance is linked to the age of the mother at the time of her pregnancy. According to them, the older the mother’s age at the time of pregnancy, the more the probability of having children of only one sex seems to increase. The number of children also appears to play a role. Women who had three or more children were statistically more likely to have exclusively daughters.
An opening to other research
At the same time, a genetic study carried out on women revealed gene variants associated with the birth of children of the same sex. Different variants would favor female or male births. It is necessary to emphasize that certain behavioral biases could have influenced the results, such as the fact that some parents insist on having children of both sexes. To avoid this discrepancy, the scientists redid the calculation without taking the cadet into account and the observed trends remained the same.
The study is nevertheless the subject of criticism from the scientific community. Some researchers say the initial sample is far too small to draw direct conclusions. A 2020 Swedish study, which was based on more than 4.7 million births, found no evidence of a genetic link in the distribution of boys/girls. Its author, geneticist Brendan Zietsch, described the main study as “fallacious”.
The research team also acknowledged the lack of sample diversity within the study. “The population studied is composed mainly of white women (95%) residing in the United States”they specify. Depending on the region in the world, gender preferences or cognitive biases vary across cultures.
