Welfare -> fatherlessness (as seen dramatically among US Africans) -> lower fertility (since Dad isn't there to give Mom a second, third, etc)

It should also be mentioned that the dominant mode of reproduction in human history is that the mean male and mean female have approximately the same number of children (since it takes one of each and the population is roughly half each sex) but the modal man has far fewer children than the modal woman (ie a few men have lots of children while many have none). With the relaxation of Christian marriage norms (but not the post-Christian welfare ethic) we have lost stable nuclear families but not yet replaced them with polygamous or tribal arrangements. 

 Interesting, thx!