More Mothers or More Fathers?

Here's a question - are there more fathers in the world, or more mothers? You may have a gut reaction that the number is equal, but that wouldn't be true. Take an example: Say we have two women (we'll call them W1 and W2), two men (M1 and M2) and two kids (K1 and K2).

Well, M1 and W1 could have produced K1, while M2 and W2 produced K2. In that case the number of mothers (2) would be equal to the number of fathers (2).

But it's possible that M1 has one child with W1 and one with W2. M2 has none. In that case, we have one father and two mothers.

You could also have one mother and two fathers, or one mother and one father.

You get the gist of it...

Well, so that brings us back to the original question - are there more mothers in the world or more fathers?

In biblical times, one could convincingly claim there were more mothers. It's the alpha male model. The stronger wealthier man married more than one woman, and therefore had many kids. Some men didn't get to have even one.

Today the tables could be turned. Some women will not have any kids, while others will have children from more then one man. If that were really true, there'd be more fathers than mothers. But what is really happening? Are there more fathers than mothers or not?

I sense this is the seed of a PhD project. Or perhaps it's already been done.