One of the books that Charles Darwin took with him on the voyage of the Beagle was Charles Lyell’s newly-published Principles of Geology. Lyell was an advocate of the uniformitarian views of James Hutton. Without getting bogged down in the details of the uniformitarianism/catastrophism debate that raged in the late 18th and early 19th centuries – although I believe most popular accounts manage to unfairly caricature both sides* – the main argument was over whether the geological record could be interpreted in terms of the processes we see operating in the modern world, or were witness to a world which followed fundamentally different rules. Lyell was, of course, an advocate of the former; and in Principles he argued that the catastrophists’ fatal error was their failure to recognise the great age of the Earth, which couldn’t help but warp their conclusions. By way of analogy, he asked his readers to imagine the results if Egyptian archaeologists of the day had
…visited that country with a firm belief that the banks of the Nile were never peopled by the human race before the beginning of the nineteenth century… it is easy to perceive what extravagant systems they would frame, while under the influence of this delusion, to account for the monuments discovered [there]. The sight of the pyramids, obelisks, colossal statues, and ruined temples, would will them with such astonishment, that… they might incline at first to refer the construction of such stupendous works to some superhuman powers of a primeval world. [p 27-28**]
We should be warranted in ascribing the erection of the great pyramid to superhuman power, if we were convinced that it was raised in one day; and if we imagine, in the same manner, a mountain chain to have been elevated, during an equally small fraction of the time which was really occupied in upheaving it, we might then be justified in inferring that the subterranean movements were once far more energetic than in our own times. [p 30**]
Lyell argued, as Hutton did before him, for the power of incremental change when it is multiplied by Deep Time. Small changes to the surface of the earth, which seem insignificant from our limited temporal perspective, can, when added together multiple times over millions of years, produce dramatic results. A river can carve a vast canyon; a series of earthquakes can build a vertiginous mountain range. Darwin clearly took this lesson on board: in his own observations of the geological processes at work in South America, he described the effects of the Concepcion earthquake, which uplifted beaches and shell-encrusted boulders along a large stretch of the west coast as “one step in the elevation of a mountain-chain”, clearly aware of how repeated small uplifts over millions of years could have eventually have resulted in the Andes.
It is striking that it is exactly this principle – the cumulative power of incremental change – that lies at the heart of Darwin’s evolutionary thesis. Just like an individual earthquake, or the tiny amount of rock carried away annually by a river, the change within species due to natural selection is quite small if considered over years or decades (although, as we have since discovered, it is observable in certain circumstances). Yet Darwin was able to grasp how far it could go, when given geological time to work with: apply consistent pressure for a few tens or hundreds of thousands of years, and those small changes start to add up.
So I’d like to suggest that Darwin’s appreciation of geological processes, and his grasp of the depth of geological time, was central to his understanding of how natural selection could shape and rework life along the widely divergent paths seen both in the wild diversity of the modern world, and the evolutionary history recorded in the fossil record. I’m not arguing that you needed to be a geologist to come up with the mechanism of Natural Selection, but I am arguing that you needed a geological perspective to truly appreciate its power. Darwin’s geological training was an essential part of the process that made The Origin of Species such a far-reaching synthesis.
Furthermore, if you want to understand why I admire Charles Darwin so much, and consider his birthday to be worthy of celebration, then consider that the mark of a great scientist, and a truly original thinker, is to take ideas and concepts outside the realm in which they were first honed, and apply them in a new one. Which is exactly what Charles Darwin did: he saw how the geological ideas of uniformitarianism and Deep Time could be profitably applied to the biological realm. Science is as much about process as results, and in his careful and detailed observations of the world around him, the rigour with which he developed his ideas, and the breadth of his thinking, Darwin provides an example that we can all look up to.
*to borrow a phrase from Brian, I believe that generally the textbooks are more cardboard than paper.
**page numbers from the Penguin Abridged edition. Google Books has scans of some of the early editions