Author Robert Kunzig takes an expansive view of the topic, from the burden of overpopulation in India to the strain of too many retirees in the Netherlands. He concludes that the answer to the question of "How many people can the world support?" is basically unknowable:
"For centuries population pessimists have hurled apocalyptic warnings at the congenital optimists, who believe in their bones that humanity will find ways to cope and even improve its lot. History, on the whole, has so far favored the optimists, but history is no certain guide to the future. Neither is science. It cannot predict the outcome of People v. Planet, because all the facts of the case-how many of us there will be and how we will live-depend on choices we have yet to make and ideas we have yet to have."