This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.

Natural selection acts solely by accumulating slight successive favorable variations, it can produce no great or sudden modification; it can act only by very short steps.

The expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient.

For forms existing in larger numbers will always have a better chance, within any given period, of presenting further favourable variations for natural selection to seize on, than will the rarer forms which exist in lesser numbers.

I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection.

All that at present can be said with certainty, is that, as with the individual, so with the species, the hour of life has run its course, ans is spent.