More about how the environment can affect sex ratios of children. The chances for a boy or a girl are a lot like the chances of getting heads. A female bluestreak cleaner wrasse can turn into a male when necessary. The Tech Interactive S.
The Claim: Some Men Are More Likely to Father Boys
Monday's medical myth: you can control the sex of your baby
I don't make this stuff up, promise. I just find it and pass it along for your perusal: "Males may alter the velocity of sperm they allocate to copulations by strategically firing their left and right ejaculatory ducts, which can operate independently. Among red junglefowl, it's attractive females that do the trick, according to an article at Discovery. Similar sperm-control mechanisms have been uncovered previously. In fact, " sperm competition " is a well-supported idea that goes way back. As often put, for males it's like trying to win the lottery: The more tickets you have, the greater your chances. But, of course, each ticket has a price.
Since the late s, scientists have explored how to produce sperm where all of the chromosomes come from a female donor. Creating female sperm was first raised as a possibility in a patent filed in  by injecting a woman's cells into a man's testicles, though the patent focused mostly on injecting altered male cells into a man's testes to correct genetic diseases. In , Japanese scientists partially confirmed such techniques by creating chicken female sperm in a similar manner. It is therefore concluded that most of the W-bearing PGC could not differentiate into spermatozoa because of restricted spermatogenesis. One potential roadblock to injecting a woman's cells into a man's testicles is that the man's immune system might attack and destroy the woman's cells.
It has long been suspected that men who come from families with plenty of males have higher odds of fathering boys, and that for men with many sisters, it is vice versa. But there was never any strong evidence. So in December, a British doctoral student put the theory to the test. In a study published in the journal Evolutionary Biology , the researcher, Corry Gellatly, examined the histories of more than American and European families dating to , involving more than half a million people.