Human beings evolved to walk 3-6 miles/day. In dense, walkable places we get the dose of walking our body needs to thrive and dozens of low stakes, interpersonal interactions our hearts need to be happy.
Isolation in a 3-ton steel pod is bad for us in every conceivable way.
Why does DENSITY make people so very HAPPY?
Short answer is that density satisfies the human need for social connection. Humans are social animals; we are not evolved for car commuting to community.
Long answer is that happiness is the psychological reward we get from participating in the social, cultural, and economic life of a dense neighborhood. It feels really good to live in a dense neighborhood, where you know a range of people, where you run into neighbors when you go for a walk, where you see familiar faces at local businesses, church, school, and so on.
In dense neighborhoods, we feel the agglomerative, creative energy of being near opportunity, culture, and work. We are embedded in multigenerational social networks that lower stress, improve health, and fight loneliness.
And their physical permanence--the built environment that enables density--gives us the sense that we are part of a living urban story that existed long before us and will continue long after us.