I'm sure you've all heard by now that Angelina Jolie finally gave birth to her twins. People Magazine reports that "multiples do run in the Pitt family: Brad's sister Julie has twin girls." I should have known better than to expect People Magazine to make a clear, relevant comment.
You see, Brad Pitt's sister having twins has absolutely NOTHING to do with Angelina having twins. Nothing. How could it?
Do multiples run in your family? is a question I'm asked ALL the time. No. Identical multiples are a random act of nature. They usually occur in younger mothers or older mothers, both of which are more likely to have weaker eggs. A weak egg splits to create identical twins, triplets, etc.
Multiples running in the family is a completely maternal factor. It means that genetically speaking, you are predisposed to release more than one egg during ovulation, resulting in fraternal multiples.
Now those are two extremes: all identical or all fraternal. There are women who have spontaneous triplets, which consist of a pair of identical twins and fraternal triplet. And there are women who have weak eggs no matter what their age.
I've never heard of multiples being a paternal factor. But we are talking about Brad Pitt...