Natural Selection and Neutral Mutations

Charles Darwin objected to all attempts to reduce his theory of evolution to its doctrine of natural selection. “Natural selection has been the main but not the exclusive means of modification,” he declared. Nonetheless, a group of self-proclaimed strict constructionist Darwinians has recently risen to prominence by reducing Darwin’s theory in just species’ form and behavior, and for the success or failure of species in general.

Natural selection is generally held to result in adaptation, the shaping of an organism’s form and behavior in response to environmental conditions to achieve enhanced reproductive success. If the strict constructionists are right, the persistence of every attribute and the survival of every species are due to such adaptation. But in fact, species whose success or failure had little to do with their adaptations.

For example, while it is true that some random mutations of genetic material produce attributes that enhance reproductive success and are thus favored by natural selection, and others produce harmful attributes that are weeded out, we now know from population genetics that most mutations fall into neither category. Research has revealed that species, but their persistence from one generation to the next is not explainable by natural selection.

Additionally, the study of mass extinctions in paleontology has undermined the strict constructionist claim that natural selection can account for every species’ success or failure. The extinction of the dinosaurs some 65 million years ago was probably caused by the impact of an extraterrestrial body. Smaller animal species are generally better able conditions caused by the impact. In a sense, their success was the result of dumb luck.