When Identical Twins Aren't as Identical as You Thought

Identical twins are formed when one fertilized egg results in two babies, who are then genetically identical. But are they really identical? The person we are is a factor of both genetics and environmental factors. Studies of identical twins separated at birth amaze us with the similarities that two people can have after being raised in different families. Genetics can be very strong- but they aren't everything. You might expect identical twins who were raised together to be, well, identical. But even when they share everything, including their mother's womb, there are environmental differences that leave a lasting mark. Did one fetus have a larger placenta? Did one twin spend more time sick as a child? Did they prefer different foods with different nutritional values? Or did either undergo a cell mutation at any point in their lives? Jaida Elcock of SciShow gives us a lot of different reasons why identical twins may not be quite identical. Knowing all this is pretty neat, but it's still not going to help you tell those two apart. There's a 50-second skippable ad at 3:30. -via Laughing Squid