I have been reading student journals from my family class. We discussed birth order and sibling competition this time. We studied Frank Sulloway's theory that children are in a Darwinian competition for parental attention. They have to differentiate themselves from their siblings. The first-borns get first choice, so they tend to try to monopolize the things that the parents value. My students are overwhelmingly first-borns or only children. Since Centre is a highly academic place, we tend to get first-borns who emphasized academic learning.
I have also been hearing about the niches chosen by the later-born children. I knew many of the options - sports, art, music, religion, service, or sheer rebellion.
Listening to the women, though, I have heard several times that sisters sometimes differentiate into "the smart one" and "the pretty one."
This made me wonder what the male equivalent would be. The closest I can get is "the smart one" and "the funny one." But the parallel is not as common or exact.
So far this is just an educated guess.