Partly influenced by An Essay on the Principle of Population (1798) by Thomas Robert Malthus, Darwin noted that population growth would lead to a "struggle for existence" in which favourable variations prevailed as others perished.
Delvist påvirket af An Essay on the Principle of Population (1798) af Thomas Malthus, bemærkede Darwin, at befolkningstilvæksten ville føre til en "kamp for tilværelsen", hvor gunstige variationer sejrede som andre omkom.