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 life and death, good and evil. Some famous twins are credited with the birth of nations, others are described as deities.
Our recent research suggests that twins were actually the norm much further back in primate evolution, rather than an unusual occurrence worthy of note. Despite the fact that almost all primates today, including people, usually give birth to just one baby, our most recent common ancestor, which roamed North America about 60 million years ago, likely gave birth to twins as the standard.
