WASHINGTON — Past studies indicating that firstborns have higher IQs than their siblings have launched speculation about why this might be (as well as taunts that the dumb middles and lastborns are too thick-skulled to push out their own competing studies). Bu floats several of these older hypotheses in reference to her results. Confluence theory states that "children's intellectual development is moulded by the intellectual environment in the family, which is a function of the average of the intellectual levels of all members of the family." So the brain climate is loftier for firstborns than for younger sisters and brothers — at least until those younger siblings are born, after which, shouldn't they be better-positioned than their elders? (Confluence theory doesn't make a ton of sense to me. Perhaps I have an older sibling I don't know about.)
Other, more plausible explanations: While parents, newly stunned by the miracle of life, invest more resources in their first child, the wondrousness has worn off by kid No. 3, who must fend for herself intellectually. Or firstborns are less constrained in their achievements by the need to differentiate themselves from a sibling — they get "first pick" of an identity, so it's more likely to fit. Or — finally, and most simply — stereotypes about eldest-child excellence coalesce into expectations, which toughen into realities.
I wish the paper had tried to account for the particular ambition of firstborn girls. (The Guardian has a pretty persuasive list of power-playing female eldests that includes Angela Merkel, Hillary Clinton, Sheryl Sandberg, J.K. Rowling, Oprah Winfrey and Beyoncé.) The result does seem to bulwark the fact that women are pulling ahead of men in educational attainment more generally, and that gifted girls prove especially vulnerable to pressure from their folks. One factor Bu and her team may have overlooked as they teased apart the family structure's role in scholastic glory? Pets. If I have accomplished anything in my career as a daughter, it has been in quixotic pursuit of being loved as much as the dog. - See more at: http://www.cnhinews.com/cnhins_features/x360414574/Firstborn-girls-are-statistically-more-likely-to-run-the-world#sthash.kGTa7w0q.dpuf