The four postulates presented by Darwin in On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (eventually shortened to On the Origin of Species) are as follows: 1) Individuals within species are variable; 2) Some of these variations are passed on to offspring; 3) In every generation, more offspring are produced than can survive; and 4) The survival and reproduction of individuals are not random; the individuals who survive and go on to reproduce the most are those with the most favorable variation, and they are naturally selected. It follows logically from these that the characteristics of the population will change with each subsequent generation until the population becomes distinctly different from the original; this process is known as evolution.