Props to the poster who mentioned Dr. Frank Dully's research. His "Sex And The Naval Aviator" is a classic analysis of the successful pilot's consititution.
Dr. Jerry Berlin did a study at American, Northwest, and TWA in the 80's, and found that over 80% of the pilots were first-born. Dr. Bob Helmrich did a similar study in the early 90's and found the same percentages in a survey done trhough NASA.
Dully's work was the ground-breaker, though. He developed a no-jeopardy survey that all of us had to take in the 70's before starting Naval Flight Training. It asked a bunch of goofy questions such as,
"How old were you when you first realized you wanted to be a pilot?"
"Do you dream about flying without an aircraft?"
"Would you rather slam you thumb in a car door, or throw up on a crowded bus?"
"Would you rather be rich or famous?"
"Are you an above-average automobile driver?"
In 1988, NAMI (Naval Aviation Medical Institute) released some of the data from his surveys. (It came out through CNATRA's office, but I haven't been able to find anybody who has a hard-copy of the report)
He was able to predict who would successfully complete Naval Flight Training, and who wouldn't. For some reason, he predicted who would succeed with more accuracy than he predicted who would fail.
Of my two fighter squadrons (F-4, F/A-18) only 2 out of 35 pilots were not first-born. I don't recall anything about right- or left-handed. (One of those two had different-colored eyes! The left was blue, the right was brown. Creepy!)
I'm a first-born, right-hander. Same color eyes.