One of the most influential books on economics ever written, An Essay on the Principle of Population remains one of the most controversial, too. Arguing that unchecked population growth will eventually outstrip food availability and lead to famine and disease, this 1798 work inspired naturalists Charles Darwin and Alfred Russel Wallace to develop the theory of natural selection. But it has also sparked criticism. To save society, Malthus proposes reining in population growth by minimizing government support for the poor, which he believes leads to more births and ultimately more hardship, and promoting sexual restraint to control population growth.