Claudia Evart, a woman who lost both her sister and her brother in separate accidents, created the day to honor the special relationships between siblings. It is on April 10 every year.

When siblings share a womb, sex hormones from a male fetus can cause lasting changes in a female littermate. This effect exists for all kinds of mammals — perhaps humans too.

About 60,000 children a year in the U.S. lose a sibling. Zion Kelly joined that unlucky group in 2017 when his twin, Zaire, was killed. Zion has learned a lot about grief, and himself, since then.

Researchers have learned a lot about blended families since the 1970s — when The Brady Bunch painted a perfect picture of stepsiblings getting along. Some of their advice might surprise you.

Sam and John Fetters are identical twins with autism. But Sam is in college, while John still struggles to form sentences. Their experience may shed light on the disorder's mix of nature and nurture.

Having siblings can mean shared family and childhood experiences — and also shared bedrooms and rivalries. A growing body of research shows us that sibling relationships can shape us for life.