With fertility falling to record lows in the United States, it is increasingly important to understand what factors may be preventing Americans from having the families they want to have. One factor that many people immediately think of is housing, cities, and density. Because children require a degree of space, people from a wide range of perspectives argue that housing affordability, open space, and housing density could all matter for family formation.

But this debate takes a particularly sharp turn in relation to the modern “YIMBY,” or “Yes In My Back Yard,” political movement seeking to eliminate laws that restrict supply of new housing. Many YIMBY advocates believe that removing these laws will lead to housing becoming more affordable (which most people believe can boost fertility), even as it will also lead to Americans living in denser communities (which some people believe may reduce fertility). In this post, I won’t settle the question over whether removing zoning laws would actually increase density (it really depends on what exact laws are changed). Rather, I’ll focus on: What would happen to fertility if density increased?