Adaptation vs. Design in Biological and Material Cultural Evolution
Darwin professed great admiration for William Paley—author of the influential treatise Natural Theology; Or, Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature (Paley 1802). Paley acknowledged the often spectacular fit between organisms and their environments—the very structures and functions that Darwin ultimately successfully demonstrated are the products of natural processes of selection of heritable variation. Paley made the case that such seemingly perfect fit between organisms and nature was de facto evidence that God had designed and created all the different organisms of the world. After all, he argued, were we to discover a watch on the ground, we would know that it must have had a designer, a builder. By analogy, Paley said, we should realize that a creative mind—the Mind of the Deity—lies behind the intricate designs we see in the organic world.
When Darwin was taking a hard look at evolutionary (“transmutational”) ideas as he collected fossils and living species in South America from 1832 to 1835 (see Eldredge 2009a), he saw patterns of replacement in time and space of closely similar species—concluding by journey’s end that natural processes underlay the generation of new species. It was only after he reached home that he confronted the problem of adaptation, for the features of organisms must evolve by natural processes—if it is true (as he had decided) that species have births and deaths, analogous to those of individuals (“Brocchi’s analogy”; see Dominici and Eldredge 2010) through natural causes.
Because Darwin’s theory has come down to us as basically a theory of adaptation, historians have naturally assumed that it was adaptation that convinced Darwin to accept evolution in the first place. But Darwin had two stumbling blocks: (1) Paley’s arguments that adaptation implies design by the creative Mind of the Deity and (2) the simple fact that, when one looks at any organism alive today, one can marvel at the features that fit them so well to their natural surroundings—but that is all. There is nothing intrinsic about the features of a single organism that demonstrate, in and of themselves, that they evolved through natural causes—rather than being designed by the Deity.
Darwin had one example while on the Beagle that showed that, even in 1832, he was looking for a natural causal understanding of the adaptations of organisms (see Eldredge, 2009a for details of Darwin’s encounter with, and thoughts about, this impressive snake species). The large poisonous snake he saw and collected at Bahia Blanca, Argentina in 1832 caught his attention; the tip of the tail was a hardened pointed structure which struck Darwin as intermediate between the simple smooth end of an Old World adder’s tail, on the one hand, and the rattle of New World rattlesnakes—which Darwin called the “more perfect” organ. As he wrote in his diary, the tail of his Bahia Blancan fer de lance “marks the passage” between the primitive tails of adders and the advanced, perfected rattles of rattlesnakes.
“Marks the passage” is about motion, of course—bespeaking a sort of fluid interconnectedness between different forms of the “same” (i.e., “homologous”) part of different, yet “closely allied,” species. Lamarck (1801) had been talking about how the features of organisms slowly are transformed naturally through time, right around the same period as Paley was developing his supernatural explanation of adaptations. But the snake was the clearest of very few such examples that Darwin recorded in his notes while on H.M.S. Beagle. Otherwise, he had really very little to say about adaptations while collecting in the field.
But, once he did arrive home, by now convinced of evolution, Darwin started looking for the natural process that could produce such exact (and some not-so-exact) matches between organisms and their environments. He read and thought about what was known about reproduction, heredity, and variation. And, as he records in his autobiography, after he read about the natural controls on population growth caused by lack of sufficient food supplies and other factors in Thomas Malthus’ Essay on Population (Malthus 1798), he suddenly “saw” the principle of what he called “natural selection”: because more organisms are produced each generation than will be able to survive and themselves reproduce (else, Darwin once wrote, the world would be “standing-room-only” in elephants), only those most closely suited to their environments will tend to survive and successfully reproduce—transmitting to their offspring the features that made them successful (though no one knew at that point in the late 1830s how and why inheritance actually works in biological systems). When new environments are encountered, different variants in the population will then become “favored” by the natural process of selection.
Adaptation through natural selection has been observed in the wild, generated experimentally in the lab, and emulated in mathematical simulations. It is one of the closest things to a natural “law” in evolutionary biology (geographic speciation is an example of another such “statistical law”). Thus, our modern understanding of adaptation is thoroughly vetted science. And that is the reason why we can look at our hands and think about our brains and confidently assert that they are, indeed, the result of natural processes—rather than the direct design product of a supernatural God. Supernatural explanations lie outside the realm of science. Science looks for natural causes of natural phenomena—and natural selection is the natural causal explanation of adaptation.
The marketplace and the experiences of people using artifacts, likewise, impose forms of selection of artifacts. Sometimes “better mousetraps” do come along—but accurate predictions of, for example, which among similar-performing cell phones will dominate the sales—always an elusive Holy Grail for manufacturers and marketers who would love to know in advance what product will succeed, and what will fail—are notoriously hard to come by. “Selection” among alternate variants of an artifact, it seems, is likely to reside as much in a fickle public’s mass decision on what is attractive or “cool,” as on any clear functional superiority of one version of an artifact over another.