We always thought your chances of having a boy or a girl were about 50-50, but it turns out that evolutionary biology may have tampered slightly with those odds. In a new study in the journal Reproductive Sciences, Satoshi Kanazawa, an evolutionary psychologist at the London School of Economics, argues that plain people are more likely to have sons than people who are beautiful. His findings were based on a 1958 survey of 17,000 English babies, in which researchers asked the kids' teachers to rate them as "attractive" or "unattractive" at age 7, and then followed up with the group 45 years later to find out what gender of children each had. Kanazawa found that the kids who were rated "attractive" had equal numbers of boys and girls, and that the "unattractive" group was more likely to have only produced sons.
Of course, Kanazawa has a theory for why this is: Men consistently rate attractiveness in women as important when seeking both long-term relationships and casual affairs. (Women, in contrast, value traits such as wealth and status as more important in the long term.) So, Kanazwa says, it would stand to reason that more daughters are born to beautiful people so that, as women, they're more likely to find a mate and procreate.
At this point, I'm just going to try not to read anything into the fact that my first child is a boy...