Who Influenced How You Grew Up More—Your Parents, or Your Siblings?

I wasn’t especially close to my older sister when we were kids, and we really weren’t close as teenagers. In fact, it wasn’t until we began to have kids of our own that we truly became friends, calling each other, exchanging advice and tips, sharing stories of first words and first steps. So I never gave much thought to whether she influenced the way I grew up. But more and more studies say she did.

In one California study, psychologist Patricia Evans found that younger sisters whose older siblings are teen moms are five times more likely to also become teen moms. Evans was working in an ob/gyn clinic when she noticed how many pregnant clients were greeted by her fellow staffers with questions like, “Aren’t you Anna’s little sister?” The staffers recognized the young women from their previous trips to the clinic with Big Sis.

And Richard Rende, a psychiatry prof at Brown University, has done studies showing that older siblings have more influence over whether their younger siblings smoke or drink than parents do. Using devices that record study participants’ behavior, Rende has even shown that sibling pairs exhibit “shadow” behavior—they tend to smoke at the same times even when they’re apart. Bad news? If your older sibling smokes, you’re 25 percent more likely to smoke, too; if your older sibling drinks, you’re 36 percent more likely to drink. Good news? Little sibs also mimic positive behavior by their elders. So, Sister Nan, I guess I should thank you for my good habits, too.

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