As the eldest of three, I'm delighted to hype a robust new Norwegian study (explained very well here in the New York Times) showing pretty conclusively that the I.Q.'s of oldest siblings are, on average, three points higher than their younger siblings. I've been telling Mom and Dad this for years -- but they won't listen!
In all seriousness, the study is profoundly important for one big reason. It's not because this huge population study (241,310 people) reveals anything about particular individual families (in our family, the youngest is the smartest). And it's not because it helps us understand how birth order might affect intelligence. Rather, it's simply because it's definitive scholarship helps chip away at the myth that we are all born with a certain intelligence. Intelligence, like all complex behavioral traits, clearly has strong genetic influences, but is ultimately a process, not a thing; like personality, it's a consequence of millions of tiny influential events from the realms of nutrition, parenting, play, sibling relationships, schooling, media exposure, and random happenings. The process starts at conception and never stops.
(This is my first post in while -- I'm still in the middle of wrestling with some of the actual content in the book, but hope to return soon to more regular posts.)