...The study shows a clear link between higher energy intake around the time of conception and the birth of sons. The findings may help explain the falling birth-rate of boys in industrialised countries, including the UK and US.
The study focused on 740 first-time pregnant mothers in the UK, who did not know the sex of their fetus. They were asked to provide records of their eating habits before and during the early stages of pregnancy. They were then split into three groups according to the number of calories consumed per day around the time they conceived. 56% of the women in the group with the highest energy intake at conception had sons, compared with 45% in the lowest group. As well as consuming more calories, women who had sons were more likely to have eaten a higher quantity and wider range of nutrients, including potassium, calcium and vitamins C, E and B12. There was also a strong correlation between women eating breakfast cereals and producing sons.
What's going on? Probably the Trivers-Willard Hypothesis:
Dr Fiona Mathews said: "Potentially, males of most species can father more offspring than females, but this can be strongly influenced by the size or social status of the male, with poor quality males failing to breed at all. Females, on the other hand, reproduce more consistently. If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times having a daughter is a safer bet."
The phenomenon of high status females producing sons and low status females biasing their offspring toward daughters is well known. Usually one doesn't need to make recourse to a prenatal process; infanticide or neglect after birth can explain the imbalances in most societies. With the spread of elite values in many "traditional" cultures the son-preference has been generalized, at least in the ideal, but one needs to be cautious about projecting back to the past.1 There is the famous finding that medieval cemeteries show more male infants who died early than female among the peasants, and the inverse among the nobility.
The paper is being published by The Proceedings of the Royal Society: B, but is not on their website.
1 - In India most low caste groups practiced brideprice until the 20th century, when they switched to dowry in imitation of the high castes.
Is it also possible that boys - which are larger babies - require a higher calorific intake to support during pregnancy, and if your diet is poor it's safer to just not risk it?
The explanation I would favour is that male fetuses (and infants) are more susceptible to environmental stresses, and have a higher mortalty, than female fetuses.
So the sex ratio of surviving infants tends to favour females more as the environment becomes more stressful (eg disease and starvation).
I would guess this is a specific example of the general phenomenon.
Or another possible explanation is that male sperms are somehow more active in a well-fitted uterus --therefore the boys.
Read this on Yahoo. Ridiculous. Although male fetuses are more likely to abort, there is a natural 105 to 100 rate in favor males. It would take serious, possibly detrimental calorie restriction to show a significant favor for female/male births, and there is no way any woman in a modern population study would go through with that, let alone enough for a proper sample for this type of study. I just hope this doesn't make it to Asia b/c there are will be some very cranky overfed mothers of girls coming after these researchers.