Replacing Yourself

Think of the first 20 people you know who have had all the kids they are likely to have. That generally means people over 40. For the purposes of this discussion, exclude anyone over 70.  Add up the adults in your group. Then add up the number of offspring they produced. Is the net gain in humans sufficient to grow the population?

When I do the math with my own circle of friends, we approximately break even, after allowing for spillage and spares. It made me wonder about the rest of the world...