Although it is certainly true that chance and accidents account for many deaths of individuals in a species, evolutionary scientists have proved that many traits and genetic proclivities do not enable the individual to withstand elements in the environs in which he lives, including the struggle for survival that especially distinguishes the life and death of the animals. It can be said that, what may be called chance or accident brings forth the deaths of individuals who would otherwise well suited to live, but given that this phenomenon goes on day by day and year by year, we find that gradually a genetic favoritism will begin to emerge.

Herbert Spencer called this process the “survival of the fittest,” and although the phrase may not be scientifically accurate in the case of any one species in any one year, when we look at that the struggle for survival is going on constantly, during the entire lifespan of each species, we cannot doubt that generally speaking those which survive are among the fittest. The struggle is so intense and so perpetual that the most minor defect in any sense organ and any physical weakness will almost surely, at one time or another, be fatal.

This relentless weeding out of the less fit, in every generation will produce two separate consequences, which require to be clearly described. The first of these is the conservation of each species in the broadest state of adjustment to the conditions of its environment. As long as these conditions continue unchanged, the result of natural selection is to maintain each well-adapted species unchanged.

The second effect is produced whenever the environmental conditions change. The most suited will more quickly adapt, and the typical process of natural selection will occur more rapidly, matching to the conditions. This process will eventually bring about complete adaptation to the new conditions. Some evolutionary scientists allow for pure chance, but maintain that the process of natural selection in weeding out the genetically unfit and thus maintaining every species in the highest state of efficiency.

The subject of natural selection and survival of the fittest does not play out significantly in the present-day argument between the adherents of evolution theory, intelligent design theory, and creation theory. In the evolution, intelligent design, creationism debate the matter of natural selection is virtually a dead end point of contention, given that evolution theory and intelligent design theory are in common accord on the issue, while creation theory denies it altogether.