Charles Darwin visited the Cape of Good Hope in mid-1836 towards the end of the five-year, round-the-world voyage of the HMS Beagle. Although he was (understandably) exhausted and keen to return home, he made good use of his only landfall in Africa. He travelled widely, made detailed observations on local geology and the fynbos biome, and met several prominent scientists.
Charles Darwin was a man of many accomplishments, and is perhaps best known for his groundbreaking theory outlined in his treatise “On the origin of species”, more descriptively called the theory of evolution by natural selection. So we think of him as a developmental ecologist, although he was actually a geologist by training. Did his visit to the Cape have any impact on the development of his epochal theory of evolution by natural selection?
Indeed, it did. The geological formations he found at the Cape had a profound impact on Darwin’s thinking about the time scale involved in his theory of evolution.
Photo: Zandrivier Farm
One geological feature that influenced Darwin’s thoughts was the presence of marine fossils, similar to species that were still alive in the nearby ocean, found in elevated rock formations. This indicated that the land had once been under the sea and had subsequently been uplifted.
This led him to consider the idea that the Earth’s surface had undergone significant changes over vast periods of time. He realized that the uplift and subsequent exposure of these marine fossils had required long periods of geological processes, such as the gradual accumulation of sediment, the subsidence of land, and the forces of uplift, followed by erosion.
On the rocky shore at Sea Point, Darwin noticed evidence of another dramatic geological phenomenon. Once-molten magma had intruded into fissures in the sedimentary rock of the Malmesbury Group. We can still observe the results of this event (believed to have occurred at a depth of some 10 km) frozen before our eyes as they were before his, a complex intermixing of the dark sedimentary rocks with the pink-brown igneous granite.
Darwin’s exposure to the geological formations at the Cape of Good Hope, along with his broader observations from his voyage on the HMS Beagle, contributed to his understanding of the concept of deep time. Deep time refers to the immense time- scales involved in geological and biological processes. The geological evidence suggested to him that the earth had existed for very much longer than the biblical timeline. This provided the necessary time for the slow, gradual processes of evolution to occur – that is, the slow accumulation of small changes within populations over long periods, leading to the gradual emergence of new species.
It’s difficult for us to comprehend how long the 4.5 billion years is that the earth has been in existence. Deep time is not part of our human experience and while we can quote numbers, we don’t really comprehend them. Suffice to say that there has been ample time for organisms to change (initially by chance) and for any beneficial changes to become established in a population if that change makes survival even slightly more likely.
Incidentally, Darwin was not impressed at all with the Cape weather. It was mid-winter, cold, dark and rainy, with bone-chilling winds. His already depressed mood was not lifted by the spectacular beauty we associate with the Fairest Cape.
You are invited to hear more about Darwin’s observations and his understanding and development of his (at the time) revolutionary theories. The always entertaining and informative Mike Bruton will give a talk on “When Darwin visited the Cape of Good Hope” at Whale Coast Conservation on Thursday 20 July at 17h30. All are welcome. Donations at the door will be appreciated.