A List of Criminal Twins, with photos! This list includes both fraternal and identical twins. Only 2% of the world's population are twins, and only 0.2% are identical twins. Why have a singleton when you can double the kids for double the fun? To this day, twins are considered exotic. Couples trying for their first child often muse that fraternal twins (one boy, one girl) would be ideal. In scientific terms, identical twins are known as "monozygotic" and fraternal twins as "dizygotic". While twins may be unusual, some researchers suggest that as many as 1 in 8 pregnancies begin as twins, however, only one fetus is brought to full term as the other disintegrates. This is known as "Vanishing Twin Syndrome". There is also such a thing as semi-identical twins in which the twins inherit identical genes from their mother, but different genes from their father. This list includes all types of twins, and they have all done something notable.