To live together in social communities, people create and maintain expectations about what is normal and what is not. Sometimes things can fall outside the range of normal and people are OK with it. You might have a neighbor who likes to wear Revolutionary War-era costumes on their evening walks around the neighborhood. Their behavior seems...

Curious Kids^[1] is a series for children of all ages. If you have a question you’d like an expert to answer, send it to This email address is being protected from spambots. You need JavaScript enabled to view it.^[2]. Are twins allergic to the same things? – Ella, age 7, Philadelphia Allergies, whether spring sneezes due to pollen or trouble breathing triggered by a certain food, are caused

Looking again through the magnifying lens at the fossil’s surface, one of us, Sabrina Curran^[1], took a deep breath. Illuminated by a strong light positioned nearly parallel to the surface of the bone, the V-shaped lines were clearly there on the fossil. There was no mistaking what they meant.

She’d seen them before, on bones that were...