Evolution

“Just So Stories” and Natural Selection

The fossil record has provided evidence of features that cannot be observed in living specimens and even of entire species that no longer exist, requiring some explanation as to what leads to extinctions of species and the mechanism by which species evolve. Particulars of physical traits can be obtained from the fossil record, the size and shape of the limbs, for instance, or the existence of feathers or fur.

Frequently, the existence of particular physical traits is simplistically or imprecisely theorized in terms of problems they ostensibly solved for ancestral species: “Why do birds have hollow bones? Because if their bones were solid, the weight would preclude flight.” The most speculative of such explanations are sometimes termed “just so stories,” taken from Rudyard Kipling's fanciful collection of children's tales of the same name published in 1902. Kipling's work presents a collection of tales told from an omniscient stance with titles such as “How the Leopard Got His Spots” and “How the Camel Got His Hump.”

Even in milder form, explanations of this sort can imply an intentionality to the rise of adaptive [Page 429]traits, as though their emergence was directed by some external force to accomplish a specific goal, a view not supported by scientific evidence nor addressed by the theory of natural selection. Rather, adaptations are best understood as after-the-fact accounts of the conditions that precipitated the survival and inheritance of particular traits, and how those particular traits may have afforded their possessor a selective advantage over other individuals lacking them.

Darwin's widely accepted formulation first appeared in his volume On the Origin of Species by Means of Natural Selection in 1859—which presents the broad theory—and was expanded in his publication in 1871 of The Descent of Man and Selection in Relation to Sex—which explicitly applies these conceptions to human evolution. What Darwin sought to describe were general laws of action that could explain diversity and change in biological evolution without regard to motivation or intentionality. Evolutionary adaptations are the result of existing conditions and the processes of inheritance and mutations resulting in the survival of some characteristics and the extinction of others. Religions may posit a prime mover or deity to provide a motivating will, whereas nonreligious views may contend that intentionality is not necessary for adaptive change to occur, because random mutations suffice to provide the basic material for evolution by natural selection. Productive beneficial adaptations arise and persist through subsequent generations, while detrimental changes are diminished or lost through subsequent generations, as individuals with beneficial traits outcompete those with detrimental ones for resources and outperform them in reproduction, passing along the genes that produce them.

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