In February 1858 Alfred Russel Wallace was ill on a small volcanic island in the Moluccas, the Spice Islands between New Guinea and Borneo. He had a fever and during the night got an insight by recalling Malthus' book on Populations , the same book that Darwin credits with giving him the his insight for Natural Selection. And the answer was clearly, that on the whole the best fitted lived. Then I at once saw, that the ever present variability of all living things would furnish that material from which, by mere weeding out of those less adapted to the actual conditions, the fittest alone would continue the race. There suddenly flashed upon me the idea of the survival of the fittest.
All organisms tend to increase in geometric proportion.
In spite of this tendency, the numbers of individuals of a given species remain more or less constant. Deduction 1 . Thus there is a struggle for existence. All organisms vary considerably. Deduction 2 .