(from article)
“Twins are normally either identical or fraternal. In the case of identical, one egg is fertilised by one sperm, but the resulting ball of cells splits in two, giving rise to two offspring with identical genetic material. In the case of fraternal, or non-identical, twins, two eggs are fertilised, each by a different sperm. The resulting siblings arise from the same pregnancy, but are no more genetically similar than siblings from the same parents born at a different time.”
SO.... one egg splits in two - Identical twins
Two eggs fertilized at same time by different sperm - Fraternal twins
Three sperm fertilize the same egg - semi-identical twins
that is not supposed to be possible; yet there is living proof that it can happen. Wow.
Multiple fathers?