What really interests me, though, is how this is being covered in the media. Some news outlets are so PC, they can't even report it w/o feeling conflicted about reporting it because it shows biased towards something.
Time is fairly unapologetic about oldest boys being smarter.
The SF Chronicle spends two-thirds of the article trying to be PC about it and pointing out, anecdotally, about how it's not always true, and reports it as “first-born kids,” which is technically less accurate.
This is so amusing to me as a journalist and as an anthropologist the way media grabs onto things even slightly sensational make a big deal out of them, and then at the same time try to hedge their bets. Although with the SF Chronicle I think it's more that they know their audience is so liberal that if they didn't write it like that they'd get tons of hate mail.