DARWIN, GEOLOGY, AND THE GROWTH OF MACROEVOLUTIONARY THEORY

Darwin acknowledged that it was the patterns he observed in the fossil record of South America in the early 1830’s, along with information from biogeography (that indicated allopatric speciation) he adduced there (including in the Galapagos), which convinced him that evolution had happened. Yet by the same token the novel mechanism he later developed to explain what caused evolution, natural selection acting gradually, was not necessarily entirely compatible with some of the patterns he observed pertaining to the fossil record and the geographic distribution of organisms. Later (1859), in the “Origin of Species”, most of the discussion of the fossil record centers around its relative inadequacy and geographic isolation is de-emphasized as a mechanism of speciation. It seems that partly there was a disconnect between his early discoveries and his later more theoretical innovations. It is interesting to see what implications this disconnect has for our understanding of the relevance of paleontology to evolutionary theory today. I will focus on these topics and argue that significant advances in evolutionary theory have come by reintegrating the fossil record, and geography, back into evolutionary theory. It is interesting to ponder why the geologically trained Darwin came to de-emphasize the fossil record as a repository of much information about the mechanisms of evolution. The reasons may partly lie in the fact that Darwin’s approach to the study of the geological record was in some ways far more modern than the approach typically used by the paleontologists of his day. Instead, Darwin the geologist was mostly a tectonic geologist who was interested in discerning rates and processes of geological change based on uniformitarian studies.