Several studies show small differences among siblings based on birth order. First-borns tend to have slightly higher IQ than second-borns, who score slightly higher than third-borns. First-borns are also slightly taller at the age of 10 than their siblings, meaning they may be better nourished. And parents may have higher expectations for their oldest children: one survey found that 35% of moms thought their oldest would do the best in school,while only 15% thought the youngest would.
Findings like these have led some scientists (including, creepily, eugenicist Francis Galton) to conclude that first-borns are predisposed to run the world. Galton and others have found a high percentage of first-borns in influential political and scientific positions. However, some say younger siblings are the real stars. In his book Born to Rebel, Frank Sulloway uses Darwin and Copernicus as examples of later-borns whose birth order allowed them to take risks and be creative, rather than pleasing parents and other authority figures. The idea that first-borns are high-achieving but law-abiding, while their younger siblings are less conventionally successful but more adventurous, has at this point reached the status of conventional wisdom.
But is it true? Psychology professor Ginger Moore says no. She tells the Times,
There is no doubt that parents treat children differently, and some of that difference may be related to birth order. [...] However, the way that parents interact with their children, the expectations they have of them and the opportunities they give them, most likely have less to do with birth order and more to do with many other factors, such as the child's personality, gender, the number of children in the family, the spacing between siblings and parental age.
The average IQ differences among siblings may be too small to mean much (and IQ test are suspect anyway), and according to Moore, the reason birth order is such a popular explanation for variation among families may be that it's easy to measure. It's also easy to amass anecdotal evidence about. Neil Bush and the famously coked-out Roger Clinton are popular examples of underachieving younger sibs, although to call George W. Bush "more successful" than his brothers is to use an interesting definition of success. But it's just as easy to find examples of later-borns who outshone their siblings. And perhaps most common of all is the family where differences between children transcend birth order.
I'm five years older than my brother, and I remember discovering that most of my friends in college were older or only children. Growing up, I cared a lot about my parents' approval and always did my homework — my brother had to be nagged. I was nerdy while my brother was well-adjusted and popular — supposedly common traits of later-borns. As we get older, however, the picture gets more complicated. I'm probably more of a risk-taker than my brother; he cares more about traditions. He's become more academic than he ever was as a kid; I gave up computer science to pursue creative writing. And some of the closest friends I've made in the last few years have been later-borns. There's pretty much only one way my brother and I currently fulfill birth order stereotypes. We're both at our parents' house right now, and while I'm working, he's sleeping.
Are Eldest Children Really A Cut Above? [TimesOnline]