Tuesday, December 16, 2008

It's evolution, baby

I was taught that the sex of children is randomly determined. Since each sperm carries with it an X or a Y chromosome, whichever one happens to get to the egg first will determine whether the baby will be a boy or a girl. So each child has essentially a 50-50 chance either way.

But I've always thought that boys run in my family. I have more than twice as many boy cousins as girl cousins. I have one sister and four brothers, two nieces and six nephews. This never looked particularly random to me.

So this guy thinks he has proved that it's not random. In fact, it's an inherited trait passed down from father to son.

"The family tree study showed that whether you’re likely to have a boy or a girl is inherited. We now know that men are more likely to have sons if they have more brothers but are more likely to have daughters if they have more sisters . . . " Mr Gellatly explains.


The study suggests that an as-yet undiscovered gene controls whether a man’s sperm contains more X or more Y chromosomes, which affects the sex of his children. On a larger scale, the number of men with more X sperm compared to the number of men with more Y sperm affects the sex ratio of children born each year.

Interesting stuff. And it means that I was right all along. As usual.



Sam said...

Most people think that it's a condition relative to the mother, whether her uterus favors one or the other. Some vague hand waving about ph or something.

Although neither of these two is satisfactory. Looking at our family, Mom and Karen follow the predominantly male pattern, betsy is even, Jeanne has to small of a sample.

Dad can't really say to follow, because his brother has mostly girls.

OVerall, this is an interesting numbers game that will never be able to figure out, because people are having much fewer children, and patterns as this need numbers to appear.

the House of Payne said...

Right. But I think that this pattern (men with more brothers having more sons) is not one we would expect to be followed every time anyway. It's a tendency that shows up in very large numbers. Our family is big enough for that pattern to show up and get noticed, but like you said, big families like these are becoming a rarity. Which sucks. Although I shouldn't complain. I'm child number 2, so my position is pretty safe no matter what. It's the future Davids of the world who should worry.

David said...

All I know is if my genes make me have more boys, then I don't have to deal with a bunch of dirtbags trying to take my little girls on dates. Let's hope it's true...

Alice Wills Gold said...

hmm....Lg has two brothers and two sisters...and 3 daughters....I always knew we were special.