WHEN Charles Darwin published The Origin of Species in November 1859 he presented it as a hasty introduction to his ideas, for which he would present further evidence in the future. So it may have seemed to him: the text was written in thirteen months after a gestation of more than twenty years. It was written in the anxiety of knowing that Alfred Russel Wallace, like Darwin himself earlier, had recently conceived of a process that Darwin would name 'natural selection'. Instead of all species having been created together at the beginning of time, or even at punctuated intervals through time, the present array of kinds throughout the world had come into being by a gradual process of genetic differentiation and selection under environmental pressures. Slight mutations could advantage individual organisms, and such mutations might then be enhanced over generations. This insight involved extinction as well as proliferation; it was disquieting in a great number of ways, however much each man later sought to palliate the disturbance.
The idea grew in both minds through extensive travel as natural historians, through detailed observation of natural phenomena around the world (not always the same parts), and through dream and reflection. In each case it seemed to the, thinker that the full force of the theory seized him after reading Thomas Malthus An Essay on the Principle Of Population ( first edition 1798), probably in the edition of 1826. Malthus argued that human population and population growth will always outrun resources of nutrition and space; therefore competition between those occupying common environments will control population.1 Scholars have since discriminated the differences between the theories of Wallace and of Darwin and have demurred at, or emphasized, Malthus's role. In 1858, though, the insight the two men shared seemed close enough to drive Darwin at last into a steady frenzy of composition.____________________