WHAT DARWIN CHANGED FOR PALEONTOLOGISTS

In The Origin of Species, Darwin invented the modern concepts of natural selection and sexual selection, laid out most of the precepts of the field of ecology, and proposed that systematics should be determined by genealogy and not by notions of similarity or divine plan. He dismissed contemporary notions of what species were, preferring a more fluid, process-based approach to speciation. And he established the rationale for a single tree of life. In a single paragraph at the end of Chapter 6, Darwin resolved the 150-year conflict in morphology between “Unity of Type” and “Conditions of Existence” by showing that the first reflected common descent and the second diversification under the process of natural selection. The logic of this argument implied that the “progression of life” seen for decades in the fossil record could now be interpreted as the register of a genealogical flowering that had a unity of descent, whereas before the existence of the fossil record was subject to any number of Romantic, transcendental, or creationist explanations. This freed paleontologists to construct genealogies of fossil forms, a step beyond the “Lyellian curves” that merely charted percentages of living forms surviving through successively distant intervals of time. It also allowed evolutionists to extrapolate from the relationships among varieties of domesticated plants and animals to the continuum of all of nature; however, it did not permit inferences about the tempo and mode of evolutionary change, which still represents an elusive rapport between microevolution and macroevolution. Far from considering the fossil record woefully incomplete, Darwin thought that it was as good as could be expected for the circumstances of its deposition, and some of his most intemperate language in the Origin was reserved for those who would not accept the reality of Deep Time and accumulated evolutionary change.