You're assuming that each of those possibilities are equally likely, which they aren't. I don't know how much it affects the numbers, but statistically there are slightly more males conceived than females. Also, there are a certain percentage that are neither male nor female.

I see.

The question we're being asked is about the odds of two disjoint events occurring together (Girl 1 followed by Girl 2), not the probability of a single event (the birth of either a boy or a girl).

I'm not sure if we can assume that biologically, inheritance of the X or Y is an even 50/50 split, since more women are born in the world than men, but I see where this is going.

I think it's the reverse actually, as I mentioned above. Either way the point still stands that it's not 50/50.

It's entirely possible I'm incorrect, but I do believe I recently covered this in my studies somewhere.

Anyone else want to weigh in?

I think there are more women in the world than men, because women have a longer life expectancy, but when it comes to babies I believe there are males than females.

According to Wikipedia:

Oh, okay. Interesting, I sort of figured it'd be the other way around since there are more Xs kicking around in the gene pool than Ys. Wonder why that is.

I don't know. It is definitely weird.

Do those recorded births only take into account infants after a certain age, or is it possible that infantcide could make up the 14+ point difference?

This topic is piquing three of my academic interests at once.

That wouldn't determine the ratio of women to men though, since women are supposed to have two X chromosomes and men determine the gender of their children, so then there are only as many X sperm around as there are men in the world.

Right, I didn't think that through.