An Essay on the Principle of Population
Early in 1837 John Gould in London revealed that the mockingbirds were separate species: Darwin was spurred into intensive research and the inception of his theory to find the mechanism introducing species. Unconventionally, he sought information from animal breeders. In September 1838, while investigating variation, averages and population statistics, he read Malthus’ "An Essay on the Principle of Population", and wrote: