New research challenges 50-50 myth: Biological sex of children may not always be random
A new study is turning our understanding of biological sex determination on its head. Long taught in biology class as a 50-50 genetic lottery between X and Y chromosomes, the sex of a child may not be entirely random. According to new findings published in Science Advances on July 18, individual families may have skewed odds toward consistently having either boys or girls — and age, genetics, and environmental factors may be involved.
Led by epidemiologist Dr. Jorge Chavarro of Harvard T.H. Chan School of Public Health, the study analyzed data from the historic Nurses' Health Study , one of the largest and longest-running fertility databases in the world. Examining more than 58,000 pregnancies between 1956 and 2015, researchers looked at patterns of sibling sex within families, maternal age, and genetic data.
While the broader population showed the expected close-to-even split between male and female births, something surprising appeared at the family level: some couples appeared more likely to have children of the same sex — and not by random chance.Approximately one in three families in the study had children all of the same sex — all boys or all girls — a figure notably higher than simple probability theory would predict, especially in families with three or more kids.The researchers developed a statistical model suggesting that each couple might have their own "unique probability" of producing a child of one sex or the other. While this individual bias remains balanced out when looking at large populations, it could significantly affect outcomes within families. 'It's not that boys or girls are more common overall, but that the odds may not actually be 50-50 for everyone,' said Dr. Chavarro.
The effect appeared even stronger in women who had their first child later in life. This suggests possible biological shifts over time, potentially influencing which type of sperm — X-carrying (girl) or Y-carrying (boy) — is more likely to fertilize the egg.As women age, for example, vaginal pH and cervical mucus composition change, potentially favoring sperm carrying specific chromosomes. X sperm tend to be larger and more resilient, possibly giving them a better chance at success in slightly more acidic environments, which can develop later in life.
The study also uncovered two genetic loci that may be linked to the likelihood of having children of the same sex. However, these genes do not appear to be directly involved in known reproductive pathways — their role is mysterious and not yet fully understood.
'These are just initial hints,' Chavarro explained. 'They point to a potential genetic influence on sex bias, but don't yet explain the mechanism.' This finding opens new doors for genetic and evolutionary biologists to explore how heritable factors may interact with environmental and physiological variables to influence offspring sex.The findings, while intriguing, are not without controversy. Australian psychologist and behavioral geneticist Dr. Brendan Zietsch remains skeptical.Zietsch previously worked on a large Swedish study analyzing millions of birth records, which found no evidence of consistent sex patterns within families. He believes that the U.S.-based cohort (95% white, mostly nurses and health professionals) may not be representative enough to make broader claims.This study could reshape how we understand fundamental reproductive biology. For couples puzzled by having multiple same-sex children — and others praying for variety — the research may provide both insight and assurance. While conception still carries an element of chance, it may not be as random as previously believed.It also raises huge questions for future research: Could IVF or fertility treatments one day account for these biological skews? Could genetics or maternal physiology be guided to increase the chances of balancing the family tree?
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Economic Times
4 days ago
- Economic Times
New research challenges 50-50 myth: Biological sex of children may not always be random
Biological sex of children may not always be random A new study is turning our understanding of biological sex determination on its head. Long taught in biology class as a 50-50 genetic lottery between X and Y chromosomes, the sex of a child may not be entirely random. According to new findings published in Science Advances on July 18, individual families may have skewed odds toward consistently having either boys or girls — and age, genetics, and environmental factors may be involved. Led by epidemiologist Dr. Jorge Chavarro of Harvard T.H. Chan School of Public Health, the study analyzed data from the historic Nurses' Health Study , one of the largest and longest-running fertility databases in the world. Examining more than 58,000 pregnancies between 1956 and 2015, researchers looked at patterns of sibling sex within families, maternal age, and genetic data. While the broader population showed the expected close-to-even split between male and female births, something surprising appeared at the family level: some couples appeared more likely to have children of the same sex — and not by random one in three families in the study had children all of the same sex — all boys or all girls — a figure notably higher than simple probability theory would predict, especially in families with three or more researchers developed a statistical model suggesting that each couple might have their own "unique probability" of producing a child of one sex or the other. While this individual bias remains balanced out when looking at large populations, it could significantly affect outcomes within families. 'It's not that boys or girls are more common overall, but that the odds may not actually be 50-50 for everyone,' said Dr. Chavarro. The effect appeared even stronger in women who had their first child later in life. This suggests possible biological shifts over time, potentially influencing which type of sperm — X-carrying (girl) or Y-carrying (boy) — is more likely to fertilize the women age, for example, vaginal pH and cervical mucus composition change, potentially favoring sperm carrying specific chromosomes. X sperm tend to be larger and more resilient, possibly giving them a better chance at success in slightly more acidic environments, which can develop later in life. The study also uncovered two genetic loci that may be linked to the likelihood of having children of the same sex. However, these genes do not appear to be directly involved in known reproductive pathways — their role is mysterious and not yet fully understood. 'These are just initial hints,' Chavarro explained. 'They point to a potential genetic influence on sex bias, but don't yet explain the mechanism.' This finding opens new doors for genetic and evolutionary biologists to explore how heritable factors may interact with environmental and physiological variables to influence offspring findings, while intriguing, are not without controversy. Australian psychologist and behavioral geneticist Dr. Brendan Zietsch remains previously worked on a large Swedish study analyzing millions of birth records, which found no evidence of consistent sex patterns within families. He believes that the U.S.-based cohort (95% white, mostly nurses and health professionals) may not be representative enough to make broader study could reshape how we understand fundamental reproductive biology. For couples puzzled by having multiple same-sex children — and others praying for variety — the research may provide both insight and assurance. While conception still carries an element of chance, it may not be as random as previously also raises huge questions for future research: Could IVF or fertility treatments one day account for these biological skews? Could genetics or maternal physiology be guided to increase the chances of balancing the family tree?
Time of India
4 days ago
- Time of India
New research challenges 50-50 myth: Biological sex of children may not always be random
A new study challenges the understanding of sex determination. It suggests families might have a bias toward having children of the same sex. The research, led by Dr. Jorge Chavarro, analyzed data from the Nurses' Health Study. Some couples were more likely to have all boys or all girls. Maternal age and genetics may play a role. Tired of too many ads? Remove Ads Same-sex siblings: More than mere coincidence? Tired of too many ads? Remove Ads Does parental age factor in? Genetics: A new frontier? Contrasting views from the scientific community Tired of too many ads? Remove Ads A new study is turning our understanding of biological sex determination on its head. Long taught in biology class as a 50-50 genetic lottery between X and Y chromosomes , the sex of a child may not be entirely random. According to new findings published in Science Advances on July 18, individual families may have skewed odds toward consistently having either boys or girls — and age, genetics, and environmental factors may be by epidemiologist Dr. Jorge Chavarro of Harvard T.H. Chan School of Public Health , the study analyzed data from the historic Nurses' Health Study , one of the largest and longest-running fertility databases in the world. Examining more than 58,000 pregnancies between 1956 and 2015, researchers looked at patterns of sibling sex within families, maternal age, and genetic the broader population showed the expected close-to-even split between male and female births, something surprising appeared at the family level: some couples appeared more likely to have children of the same sex — and not by random one in three families in the study had children all of the same sex — all boys or all girls — a figure notably higher than simple probability theory would predict, especially in families with three or more researchers developed a statistical model suggesting that each couple might have their own "unique probability" of producing a child of one sex or the other. While this individual bias remains balanced out when looking at large populations, it could significantly affect outcomes within families.'It's not that boys or girls are more common overall, but that the odds may not actually be 50-50 for everyone,' said Dr. effect appeared even stronger in women who had their first child later in life. This suggests possible biological shifts over time, potentially influencing which type of sperm — X-carrying (girl) or Y-carrying (boy) — is more likely to fertilize the women age, for example, vaginal pH and cervical mucus composition change, potentially favoring sperm carrying specific chromosomes. X sperm tend to be larger and more resilient, possibly giving them a better chance at success in slightly more acidic environments, which can develop later in study also uncovered two genetic loci that may be linked to the likelihood of having children of the same sex. However, these genes do not appear to be directly involved in known reproductive pathways — their role is mysterious and not yet fully understood.'These are just initial hints,' Chavarro explained. 'They point to a potential genetic influence on sex bias, but don't yet explain the mechanism.'This finding opens new doors for genetic and evolutionary biologists to explore how heritable factors may interact with environmental and physiological variables to influence offspring findings, while intriguing, are not without controversy. Australian psychologist and behavioral geneticist Dr. Brendan Zietsch remains previously worked on a large Swedish study analyzing millions of birth records, which found no evidence of consistent sex patterns within families. He believes that the U.S.-based cohort (95% white, mostly nurses and health professionals) may not be representative enough to make broader study could reshape how we understand fundamental reproductive biology. For couples puzzled by having multiple same-sex children — and others praying for variety — the research may provide both insight and assurance. While conception still carries an element of chance, it may not be as random as previously also raises huge questions for future research: Could IVF or fertility treatments one day account for these biological skews? Could genetics or maternal physiology be guided to increase the chances of balancing the family tree?
Time of India
16-07-2025
- Time of India
454 hints that a chatbot wrote part of a biomedical researcher's paper
The AI tools tend to use words, like delves, crucial, potential, significant and important, far more often than human authors do Scientists know it is happening, even if they don't do it themselves. Some of their peers are using chatbots, like ChatGPT, to write all or part of their papers. In a paper published this month in journal Science Advances, Dmitry Kobak of University of Tubingen and his colleagues report that they found a way to track how often researchers are using AI chatbots to write the abstracts of their papers. The AI tools, they say, tend to use certain words - like "delves," "crucial," "potential," "significant" and "important" - far more often than human authors do. The group analysed word use in the abstracts of more than 15 million biomedical abstracts published between 2010 and 2024, enabling them to spot the rising frequency of certain words in abstracts. The findings tap into a debate in the sciences over when it is and is not appropriate to use AI helpers for writing papers. When ChatGPT was introduced in Nov 2022, a collection of words started showing up with unusual frequency. Those words, the investigators report, were not used so often before the release of ChatGPT. They infer the change in word usage is a telltale sign of AI. by Taboola by Taboola Sponsored Links Sponsored Links Promoted Links Promoted Links You May Like An engineer reveals: One simple trick to get internet without a subscription Techno Mag Learn More Undo In 2024, there were a total of 454 words used excessively by chatbots, the researchers report. Based on the frequency of the AI-favoured words, Kobak and his team calculate that at least 13.5% of all biomedical abstracts appeared to have been written with the help of chatbots. And as many as 40% of abstracts by authors from some countries writing in a few less selective journals were AI-generated. Those numbers, said Adam Rodman, director of AI programmes at Beth Israel Deaconess Medical Centre in Boston, "are almost certainly a lower bound", because they don't account for human editing of what the chatbot wrote or the chatbot editing of what humans wrote. Rodman was not involved in the study. Kobak said he was "somewhat surprised" to see so much use of AI in abstracts, summaries of papers' results and conclusions that often are the only things people read. (Kobak and colleagues said no AIs were used in the writing of their paper.) In academic sciences, some researchers have grown wary of even a whiff of AI assistance in their publications. Computer scientists are aware AI favours certain words, although it's not clear why, said Subbarao Kambhampati, a professor of computer science at Arizona State University and past president of Association for Advancement of AI. Some scientists, he said, have been deliberately refraining from using words like "delve" for fear of being suspected of using AI as a writing tool. Other scientists seem blase about the risk of being caught using chatbots. The journal Nature recently surveyed more than 5,000 researchers and asked when, if ever, is it OK to use AI to write a paper. There was no consensus. Opinions varied, depending on whether AI was used to write an abstract, or entire paper, and whether it was used to edit or summarise. For the situation analysed in the new paper - writing an abstract - 23% respondents said it was OK to use AI without acknowledging assistance, 45% said it was acceptable only if researcher reported using AI, and 33% said it was never acceptable.
