Not an economist, but I have recently been thinking about it. Probably there are lots of factors, but it seems to me that people are resourceful (if they are unemployed, they'll seek ways to survive/find employment). Also I think they'll tend to only have children when it seems economically viable to do so. As an example, consider coal miners (they've gone out of business in my country). I suspect as long as mining was a viable line of work, they continued having children and producing more coal miners. Now that it has gone away, there are lots of unemployed ex-miners for a while. But I suspect those who fail to find other sources of income won't have that many children, so eventually that "strain" of unemployment will just phase out of society. In the end, only those people with viable jobs survive.