"In October 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long- continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to work".

Charles Darwin, from his autobiography. (1876)

http://www.ucmp.berkeley.edu/history/malthus.html

Thomas Malthus (1766-1834)

The histories of mankind . . . are histories only of the higher classes.

Population, when unchecked, increases in geometrical progression of such a nature as to double itself every twenty-five years.

Subsistence increases only in an arithmetical ratio.

[Survival is] the perpetual struggle for room and food.