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Humans aren't alone
If you think it's hard to manage the birth-order issues in your family, be thankful you're not an egret or an orange blossom. Egrets are not the intellectual heavyweights of the animal kingdomor even the bird worldbut nature makes them remarkably cunning when it comes to planning their families. Like most other birds, egrets lay multiple eggs, but rather than brooding them all the same way so that the chicks emerge on more or less the same day, the mother begins incubating her first and second eggs before laying the remaining ones in her clutch. That causes the babies to appear on successive days, which gives the first-arriving chick the earliest crack at the food and a 24-hour head start on growth. The second-hatched may not have too difficult a time catching up, but the third may struggle. The fourth and beyond will have the hardest go, getting pushed aside or even pecked to death if food, water and shelter become scarce. All that makes for a nasty nursery, but that's precisely the way the mother wants it. "The parents overproduce a bit," says Douglas Mock, professor of zoology at the University of Oklahoma, "maybe making one more baby than they can normally afford to raise and then letting it take the fall if the resource budget is limited."
Orange trees are even tougher on their young. A typical orange tree carries about 100,000 pollinated blossoms, each of which is a potential orange, complete with the seeds that are potential trees. But in the course of a season, only about 500 oranges are actually produced. The tree determines which ones make the cut, shedding the blossoms that are not receiving enough light or that otherwise don't seem viable. It is, for a tree, a sort of selective termination on a vast scale. "You've got 99% of the babies being thrown out by the parent," says Mock. "The tree just drops all the losers."
Even mammals, warm-blooded in metabolism andwe like to thinktemperament, can play a similarly pitiless game. Runts of litters are routinely ignored, pushed out or consigned to the worst nursing spots somewhere near Mom's aft end, where the milk flow is the poorest and the outlook for survival the bleakest. The rest of the brood is left to fight it out for the best, most milk-rich positions.
Humans, more sentimental than birds, trees or litter bearers, don't like to see themselves as coming from the same child-rearing traditions, but we face many of the same pressures. As recently as 100 years ago, children in the U.S. had only about a 50% chance of surviving into adulthood, and in less developed parts of the world, the odds remain daunting. It can be a sensible strategy to have multiple offspring to continue your line in case some are claimed by disease or injury.
While the eldest in an overpopulated brood has it relatively easygetting 100% of the food the parents have availablethings get stretched thinner when a second-born comes along. Later-borns put even more pressure on resources. Over time, everyone might be getting the same rations, but the firstborn still enjoys a caloric head start that might never be overcome.
Food is not the only resource. There's time and attention too and the emotional nourishment they provide. It's not for nothing that family scrapbooks are usually stuffed with pictures and report cards of the firstborn and successively fewer of the later-bornsand the later-borns notice it. Educational opportunities can be unevenly shared too, particularly in families that can afford the tuition bills of only one child. Catherine Salmon, an assistant professor of psychology at the University of Redlands in Redlands, Calif., laments that even today she finds it hard to collect enough subjects for birth-order studies from the student body alone, since the campus population is typically overweighted with eldest sibs. "Families invest a lot in the firstborn," she says.
All of this favoritism can become self-reinforcing. As parental pampering produces a fitter, smarter, more confident firstborn, Mom and Dad are likely to invest even more in that child, placing their bets on an offspring whoin survival terms at leastis looking increasingly like a sure thing. "From a parental perspective," says Salmon, "you want offspring who are going to survive and reproduce."
Firstborns do more than survive; they thrive. In a recent survey of corporate heads conducted by Vistage, an international organization of ceos, poll takers reported that 43% of the people who occupy the big chair in boardrooms are firstborns, 33% are middle-borns and 23% are last-borns. Eldest siblings are disproportionately represented among surgeons and M.B.A.s too, according to Stanford University psychologist Robert Zajonc. And a recent study found a statistically significant overload of firstborns in what isor at least ought to bethe country's most august club: the U.S. Congress. "We know that birth order determines occupational prestige to a large extent," says Zajonc. "There is some expectation that firstborns are somehow better qualified for certain occupations."
Little sibs, big role
For eldest siblings, this is a pretty sweet deal. There is not much incentive for them to change a family system that provides them so many goodies, and typically they don't try to. Younger siblings see things differently and struggle early on to shake up the existing order. They clearly don't have size on their side, as their physically larger siblings keep them in line with what researchers call a high-power strategy. "If you're bigger than your siblings, you punch 'em," Sulloway says.
But there are low-power strategies too, and one of the most effective ones is humor. It's awfully hard to resist the charms of someone who can make you laugh, and families abound with stories of last-borns who are the clowns of the brood, able to get their way simply by being funny or outrageous. Birth-order scholars often observe that some of history's great satiristsVoltaire, Jonathan Swift, Mark Twainwere among the youngest members of large families, a pattern that continues today. Faux bloviator Stephen Colbertwho yields to no one in his ability to get a laughoften points out that he's the last of 11 children.
Such examples might be little more than anecdotal, but personality tests show that while firstborns score especially well on the dimension of temperament known as conscientiousnessa sense of general responsibility and follow-throughlater-borns score higher on what's known as agreeableness, or the simple ability to get along in the world. "Kids recognize a good low-power strategy," says Sulloway. "It's the way any sensible organism sizes up the niches that are available."
Even more impressive is how early younger siblings develop what's known as the theory of mind. Very small children have a hard time distinguishing the things they know from the things they assume other people know. A toddler who watches an adult hide a toy will expect that anyone who walks into the room afterward will also know where to find it, reckoning that all knowledge is universal knowledge. It usually takes a child until age 3 to learn that that's not so. For children who have at least one elder sibling, however, the realization typically comes earlier. "When you're less powerful, it's advantageous to be able to anticipate what's going on in someone else's mind," says Sulloway.
Later-borns, however, don't try merely to please other people; they also try to provoke them. Richard Zweigenhaft, a professor of psychology at Guilford College in Greensboro, N.C., who revealed the overrepresentation of firstborns in Congress, conducted a similar study of picketers at labor demonstrations. On the occasions that the events grew unruly enough to lead to arrests, he would interview the people the police rounded up. Again and again, he found, the majority were later- or last-borns. "It was a statistically significant pattern," says Zweigenhaft. "A disproportionate number of them were choosing to be arrested."