As you eat your dinner tonight – There, you may see a brother, a sister, a step-sibling, a twin. And maybe they’re your friend, and maybe they’re your enemy, but one thing is for certain: Their very existence has had a profound influence on your life.
For most of history, psychologists thought of the study of siblings as backwater: Parenting was important — siblings were not.
Siblings shares genes but rarely personalities –
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.
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.
Turns out that on tests that measure personality — stuff like how extroverted you are, how conscientious — siblings are practically like strangers.
Theory One: Divergence
The first is a view popularized by a Darwin scholar named Frank Sulloway. In Sulloway’s view, competition is the engine that pushes evolution — just as in the wild. Therefore, in the context of a family, one of the main things that’s happening is that children are competing for the time, love and attention of their parents. Aka sibling Rivalry.
Theory Two: Environment
The second theory has a slightly confusing name; it’s called the non-shared environment theory, and it essentially argues that though from the outside it appears that we are growing up in the same family as our siblings, in very important ways we really aren’t. We are not experiencing the same thing.
Theory Three: Exaggeration
The final theory is the comparison theory, which holds that families are essentially comparison machines that greatly exaggerate even minor differences between siblings.
Imagine, says McHale, two friendly children born in the same family. “One of those children is incredibly extroverted, and the other is just very sociable,” says McHale. In the context of any other family, says McHale, the second child would be considered an extrovert. “But in this family,” says McHale, “she’s the introvert.”
And once the introvert label is assigned — even if in an absolute sense it’s not really true — it influences the choices that the child makes.
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