Twins are relatively uncommon and often fascinate people. One set of twin sisters have caused a stir after disclosing a difference in their appearance that's only noticeable in the summer ...

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 ...

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 ...