Some of the worst places to live in the world (Somalia, Sudan, Gaza, etc) also have the highest birth rates. I'm sure the lack of birth control contributes here, but I still feel like we're missing a piece of the puzzle. In any case, "comfortable living space" is something only wealthy first-world couples think about before having children -- and those couples usually end up childless whether or not they have that space.

Fertility rates in most developed countries go down, not up, as couples get richer. Poor couples think they'd have more kids if only they had more money, a bigger house, access to good schools, etc. but the couples who have all that stuff are actually having fewer kids than anyone else.