By Lily Rothman
April 10, 2015

Our brothers and sisters are often the only people in our lives from beginning to end, and their influence is just as broad as that timeline.

That was the conclusion reached by TIME’s Jeffrey Kluger in a 2006 cover story about the effects of sibling-hood. And, as many U.S. states mark Siblings Day on April 10, there’s no better time to look at that research as another reason to be thankful for those closest of relatives. Even the ever-present sibling rivalry can pay off in the long run, it turns out, as they help kids grow up with problem-solving know-how.

Read TIME’s new special report on siblings: How Parents Can Help Their Kids Get Along

And, as Kluger reported, it’s not really surprising that those childhood companions end up affecting our adulthood:

Still, folks without siblings shouldn’t despair: All that research into siblings came along with research into only-children. The stereotype of the spoiled only child, scientists found, was mostly just a myth.

Read the full story, here in the TIME Vault: The New Science of Siblings

Read next: Facebook Reveals How Common It Is For Siblings to Have The Same First Initial

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