Birth order theories are interesting, especially with regard to first borns and later borns. Here’s an article from Time Magazine, The Power of Birth Order
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.”