The special relationship between twins allows researchers to examine the differences between genetic and environmental influences over both physical and mental health, as well as traits and behaviors.

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 ...

From Romulus and Remus—the myth of the twin brothers who founded the city of Rome—to the synchronized speech of Australia's "Twinnies" Paula and Brigette Powers, identical siblings have long inspired ...

These babies are identical twins, but their mom has no trouble telling them apart. “People say, ‘The doctors lied to you. Your twins aren’t identical,’” Danielle Marple of Venice, Florida, tells TODAY ...

LONDON (Reuters) - Twin sisters are more likely than other women to have a premature menopause, scientists said on Tuesday. Menopause usually occurs around the age of 50. But early menopause, or ...

These babies are identical twins, but their mom has no trouble telling them apart. “People say, ‘The doctors lied to you. Your twins aren’t identical,’” Danielle Marple of Venice, Florida, tells TODAY ...