בפרק המסכם של הספר של דרווין "…On the origin of species" נכתב:
These laws, taken in the largest sense, being
Growth with Reproduction; Inheritance which is almost implied by reproduction;
Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the (Extinction of less-improved forms (1859:489-490
על מה ביסס דרווין את טענתו המובלטת בפונט עבה: