This is interesting. Confirmation of something which has been seen in other species but not (at least as far as I know) in humans.
The first evidence that women can influence the sex of their child by what they eat before they become pregnant is published today.
The study, which links higher energy intake around conception to the birth of sons, provides the first explanation of why the number of boy babies is in decline in the west, suggesting it is the result of women consuming low fat foods and skipping breakfast, among other things.
In times of plenty, more sons are born, in hard times, more daughters. The reason is:
The work complements studies of other animals that shows that more sons are produced when a mother has plentiful resources or is high ranking, reflecting how boys are more taxing to raise.
"Boys breast feed for longer and for more," she says. "There is evidence from traditional societies that mothers invest more time in bringing up boys. And 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, where lean times are linked with daughters, has been most extensively studied in insects, but is also seen in horses, cows and some species of deer.
Dr Mathews adds: "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. The mechanism is not yet understood in mammals, but it is known from IVF research that high glucose levels encourage the development of male embryos while inhibiting female embryos. In humans, skipping breakfast depresses glucose levels and so may be interpreted by the body as indicating poor environmental conditions and low food availability.
If you\’re going to raise a scrawny son because of the shortage of resources, said son is unlikely to breed, a scrawny daughter is more likely to breed than a scrawny son.
No, I\’m not a scientist, most certainly not a biologist, but I would assume that the sex selection takes place at implanation or not of the blasotocyst (if that\’s the correct word?).