Role models, rivals, allies: sisters and brothers accompany us throughout our lives. Research shows the resources that go into this unique relationship.

A flowerpot featured on Pinterest reads, “Siblings are different flowers from the same garden.” The saying can also be found beautifully illustrated on cushion covers, postcards and signs. Many siblings would probably sign it immediately. Not only are our brothers and sisters most similar to us genetically, we also have a close, lifelong relationship—even if we often have very different personalities and choose different lifestyles.