It could not have been easy being Elliott Roosevelt. If the alcohol wasn't getting him, the morphine was. If it wasn't the morphine, it was the struggle with depression. Then, of course, there were the constant comparisons with big brother Teddy.  In 1883, the year Elliott began battling melancholy, Teddy had already published his first book and been elected to the New York State assembly. By 1891about the time Elliott, still unable to establish a career, had to be institutionalized to deal with his addictionsTeddy was U.S. Civil Service Commissioner and the author of eight books. Three years later, Elliott, 34, died of alcoholism. Seven years after that, Teddy, 42, became President.  Elliott Roosevelt was not the only younger sibling of an eventual President to cause his family heartachesor at least headaches. There was Donald Nixon and the loans he wangled from billionaire Howard Hughes. There was Billy Carter and his advocacy on behalf of the pariah state Libya. There was Roger Clinton and his year in jail on a cocaine conviction. And there is Neil Bush, younger sib of both a President and a Governor, implicated in the savings-and-loan scandals of the 1980s and recently gossiped about after the release of a 2002 letter in which he lamented to his estranged wife, "I've lost patience for being compared to my brothers."  Welcome to a very big club, Bro. It can't be easy being a runt in a litter that includes a President. But it couldn't have been easy being Billy Ripken either, an unexceptional major league infielder craning his neck for notice while the press swarmed around Hall of Famer and elder brother Cal. It can't be easy being Eli Manning, struggling to prove himself as an NFL quarterback while big brother Peyton polishes a Super Bowl trophy and his superman stats. And you may have never heard of Tisa Farrow, an actress of no particular note beyond her work in the 1979 horror film Zombie, but odds are you've heard of her sister Mia.  Of all the things that shape who we are, few seem more arbitrary than the sequence in which we and our siblings pop out of the womb. Maybe it's your genes that make you a gifted athlete, your training that makes you an accomplished actress, an accident of brain chemistry that makes you a drunk instead of a President. But in family after family, case study after case study, the simple roll of the birth-date dice has an odd and arbitrary power all its own.  The importance of birth order has been knownor at least suspectedfor years. But increasingly, there's hard evidence of its impact. In June, for example, a group of Norwegian researchers released a study showing that firstborns are generally smarter than any siblings who come along later, enjoying on average a three-point IQ advantage over the next eldestprobably a result of the intellectual boost that comes from mentoring younger siblings and helping them in day-to-day tasks. The second child, in turn, is a point ahead of the third. While three points might not seem like much, the effect can be enormous. Just 2.3 IQ points can correlate to a 15-point difference in sat scores, which makes an even bigger difference when you're an Ivy League applicant with a 690 verbal score going head to head against someone with a 705. "In many families," says psychologist Frank Sulloway, a visiting scholar at the University of California, Berkeley, and the man who has for decades been seen as the U.S.'s leading authority on birth order, "the firstborn is going to get into Harvard and the second-born isn't."  The differences don't stop there. Studies in the Philippines show that later-born siblings tend to be shorter and weigh less than earlier-borns. (Think the slight advantage the 6-ft. 5-in. [196 cm] Peyton Manning has over the 6-ft. 4-in. [193 cm] Eli doesn't help when he's trying to throw over the outstretched arms of a leaping lineman?) Younger siblings are less likely to be vaccinated than older ones, with last-borns getting immunized sometimes at only half the rate of firstborns. Eldest siblings are also disproportionately represented in high-paying professions. Younger siblings, by contrast, are looser cannons, less educated and less strapping, perhaps, but statistically likelier to live the exhilarating life of an artist or a comedian, an adventurer, entrepreneur, GI or firefighter. And middle children? Well, they can be a puzzleeven to researchers.  For families, none of this comes as a surprise. There are few extended clans that can't point to the firstborn, with the heir-apparent bearing, who makes the best grades, keeps the other kids in line and, when Mom and Dad grow old, winds up as caretaker and executor too. There are few that can't point to the lost-in-the-thickets middle-born or the wild-child last-born.  Indeed, to hear families tell it, the birth-order effect may only be getting stronger. In the past, girls were usually knocked out of the running for the job and college perks their place in the family should have accorded them. In most other ways, however, there was little to distinguish a first-, second- or third-born sister from a first-, second- or third-born brother. Now, with college and careers more equally available, the remaining differences have largely melted away.  "There are stereotypes out there about birth order, and very often those stereotypes are spot-on," says Delroy Paulhus, a professor of psychology at the University of British Columbia in Vancouver. "I think this is one of those cases in which people just figured things out on their own."  But have they? Stack up enough anecdotal maybes, and they start to look like a scientific definitely. Things that appear definite, however, have a funny way of surprising you, and birth order may conceal all manner of hidden dimensionswithin individuals, within families, within the scientific studies. "People read birth-order books the way they read horoscopes," warns Toni Falbo, professor of educational psychology at the University of Texas. "'I'm a middle-born, so that explains everything in my life'it's just not like that." Still, such skepticism does not prevent more and more researchers from being drawn to the field, and as they are, their findings, and the debate over them, continue to grow.
Parents insist that how kids turn out depends on when they were born. More and more, science agrees