Hannibal, N.Y. — Olive Somers is right-handed. Harley Somers is left-handed. Olive wears blue shoes. Harley wears pink shoes. Olive prefers a ponytail or a braid. Harley likes a bun. It didn’t use to ...

For more than a century, scientists have debated whether intelligence is mostly a product of nature or nurture. Identical twins—those born with the same genetic blueprint—have long been the perfect ...

Identical, or monozygotic, twins develop from the same fertilized egg that splits into two. These twins are the same sex and share the same genes. Sometimes called paternal twins, identical twins ...