I discuss prescient theoretical work by Marc Nerlove and coauthors on population and environmental dynamics, including whether world population will eventually reach a steady state and if so, whether such a steady state will be an dystopic one where the planet is overpopulated and environmentally degraded with low wages and welfare per capita, or more of a utopic one, with a smaller population where higher environmental quality and per capital wages and welfare can be sustained. I consider his theoretical predictions in light of four decades of subsequent research and experience on population, economic growth, and climate change. Though the future remains highly uncertain, my reading of the evidence agrees with the pessimistic conclusion of Nerlove and Meyer (1997) that “the unpriced nature of environmental resources leads parents to fertility decisions which, while optimal from their own selfish point of view, ultimately lead to environmental disaster.” I discuss the worldwide slowdown in fertility but express doubt that the deceleration in population growth is sufficient by itself to reduce the likelihood of environmental disaster. The biggest threat to the biosphere is uncontrolled growth in per capita output, absent a ‘silver bullet’ technological solution to the climate crisis.