For most of history, psychologists thought of the study of siblings as backwater: Parenting was important \u201d\u201d siblings were not.<\/p>\n
Then in the 1980s, a researcher named Robert Plomin published a surprising paper in which he reviewed the three main ways psychologists had studied siblings: physical characteristics, intelligence and personality. According to Plomin, in two of these areas, siblings were really quite similar.<\/p>\n
Physically, siblings tended to differ somewhat, but they were a lot more similar on average when compared to children picked at random from the population. That’s also true of cognitive abilities.<\/p>\n
“The surprise,” says Plomin, “is when you turn to personality.”<\/p>\n
Turns out that on tests that measure personality \u201d\u201d stuff like how extroverted you are, how conscientious \u201d\u201d siblings are practically like strangers.<\/p>\n