Ever heard of "heteropaternal superfecundation"? It's an extremely rare phenomenon by which fraternal twins can be fathered by two different men. The term made headlines back in 2015 when a New Jersey ...

Twins have been rare in human history and for that reason can seem special. Many cultures associate twins with health and vitality, while others see them as a philosophical reminder of the duality of ...

From uncanny coincidences to shared biology, we asked the experts to explain the real forces behind the phenomenon. Twins sit near Lake Geneva in Lausanne, Switzerland. Studies suggest that the ...