As a parent of two grown children who are miles apart in personality, job and lifestyle choices and interests (as far apart as, say, the writings of Jane Austen and H.P. Lovecraft) I listened with considerable interest and some amusement last week to Alix Spiegel’s NPR report on current research into sibling differences.

Although studies have found that siblings tend, on average, to share physical characteristics and intelligence, they’re “practically like strangers” when it comes to personality, Spiegel noted.

“In fact,” said Spiegel, “in terms of personality, we are similar to our siblings only about 20 percent of the time. Given the fact that we share genes, homes, routines and parents, this makes no sense. What makes children in the same family so different?”

Researchers offered Spiegel three theories:

The first is Darwinian. This theory proposes that because children compete for their parents’ time and attention, they “specialize” and develop personality niches within the family — along the lines of Darwin’s principle of divergence. “So if one child in a family seems to excel at academics,” explained Spiegel, “the other child — consciously or unconsciously — will specialize in a different area, like socializing.”

The second theory is called the non-shared environment theory. It proposes that although kids may grow up in the same family, their experiences are very different. Part of this difference may be because they’re not at the same age during major family events, such as a divorce, a death or a move across country. Thus, these events affect each sibling differently. Or it simply may be because their parents treat them differently (even when they’re trying not to do so).

The third theory — the comparison theory — proposes that minor differences in personalities between siblings become exaggerated within families. Two children, for example, may both be sociable, but one is not quite as outgoing as the other and so becomes labeled by the family as an introvert — a label that then influences all that child’s later choices.

I’m not sure which (if any) of these theories explains my children’s disparate personalities. But I actually think it’s more fun when family members aren’t cut from the same cloth, as my mother (who shared little in personality with her siblings) would have said. Makes for much livelier conversations during holiday dinners.

You can read and/or listen to Spiegel’s broadcast here.