Twins come about by heredity through previous family history. This is because genes are transferred from parents to children from one generation to the other, suggestive of family history. There are so many instances where you may find more than one twin birth between siblings, uncles, cousins and other extended family members. Children of twins giving birth to sets of twins or a mother/father from a family of twins also having twins would suggest family history as a factor in twin birth due to the genes running through them.
Mrs. Rhema Korleson
Based on my knowledge of science, twins do not only come as a result of family history. If it has happened in the family before it is likely to reoccur in the bloodline based on genetics. However, scientifically, it has to do mainly with the number of eggs released or fertilized or when a fertilized egg splits into two.