Is it true that giving birth to twins runs in families?
It’s not true for identical twins, but it is true for fraternal twins. Unlike identical twins, who both come from the same fertilized egg, fraternal twins develop from two different eggs released at the same time. (Although they have the same birthday, fraternal twins are genetically no more alike than any other siblings.) The tendency to release more than one egg in a single cycle (hyperovulation) is a genetic trait that can be passed from mother to child. Women of African origin are twice as likely as Caucasian women and four times as likely as Asian women to give birth to fraternal twins. Hyperovulation also happens for other reasons that have nothing to do with genetics. Women in their early 30s, for example, are significantly more likely than women under 20 to release more than one egg at a time. (This tendency starts to decrease after the age of 35, however.) Contrary to widespread belief, twinning doesn’t skip a generation, although it may sometimes appear to when a son inherits
