Darwin and Evolution
The words Darwin and evolution are nowadays associated in our minds. Nowadays,also, biologists take for granted that evolution occurred, but that wasn’t the case 150 years ago, when Charles Darwin introduced his ideas. As a boy, young Charles developed a keen passion for nature. He was the kind of kid who loved to walk in the woods, collect bugs, go hunting and fishing. He generally spent time learning about different kinds of plants and animals.
When he was only 16, he was sent to medical school. He found it “distasteful” and soon left the university without a degree. It wouldn’t do for a young man of Darwin’s social status to not study for some career. So, Darwin enrolled in Cambridge University to study theology, with the goal of entering the clergy. The fact that Darwin went to complete a bachelor’s degree in theology may sound a little surprising to us, but it isn’t really. The study of natural history in the early 1800’s was a monopoly of the clergy. Biology was done in what was called natural theology, describing nature in order to more fully appreciate the glory of God. Some of the most important natural historians of the time were clergymen. Mendel himself was a monk.
This seemed to Darwin to be a good way to pursue his true passions. Darwin excelled at his studies. After graduating he was offered a unique opportunity, he was asked to serve as the official naturalist on a five-year long voyage around the world on the Beagle. Darwin’s job was twofold; first, he was to provide interesting conversation to the ship’s captain for five years. Second, and more importantly, he was to acquire and catalog plant and animal specimens from every place the ship visited. This voyage changed forever the history of Darwin and evolution.
When Darwin started his voyage around the world, a long held view in science, and one that Darwin himself almost certainly subscribed to, was that all organisms were formed by a special creation, much as it is described in the book of Genesis. More importantly, it was generally held that species remained immutable throughout all time. This view isn’t just a Christian idea, some Greek philosophers talked about evolution, but Plato and Aristotle argued that species must be immutable. The idea that species living today were completely unchanged throughout time had been a dominant view in western culture for several thousand years.
Early Evidence for Evolution
Early in the 1800’s, there were a few scientific findings that began to suggest this view of immutability of species was not entirely correct. There were three general kinds of evidence that were challenging to the idea of immutable creation. The first sort of evidence came from the field of geology. Creationist views of the world argued that the Earth was relatively young. Archbishop Ussher calculated that the Earth was created in 4004. Geologists who studied landforms, however, saw evidence that convinced them that the Earth had to be a lot older than this. Many people today still challenge these well established views, as well as Darwin and evolution, arguing that Ussher's date was right.
Geological analysis showed that the Earth might be millions of years older. Second, geologists saw that landscape features had obviously undergone many radical transformations. You only have to drive along an interstate highway to see the folding in the rocks. Third, geologists began to realize that physical forces at work in nature today could explain the transformations in landforms that must have occurred in the distant past. For example, they saw how erosion, if given enough time, could lead to landscape transformation, such as the creation of a canyon.
These ideas were developed completely by the leading geologist of Darwin’s day, Charles Lyell, who in the 1820’s formally developed the idea of geological gradualism. The theory of gradualism argued that large-scale changes in the geological features of the Earth could be explained by the gradual accumulation of many small changes over a very long period of time. Charles Lyell theory and his book had a profound influence on Darwin and evolution.
The word evolution simply means change. What geology did was to show that the physical world, at least, could have changed over a long period of time.
Homologues and Vestigial Structures
Another kind of evidence that began challenging the immutability of biological species came from the work of comparative anatomists. At the time, biology was largely a descriptive enterprise, involving the collection, dissection and description of different kinds of plants and animals. In the process of doing this kind of description, anatomists noticed that very different-looking animals shared some of the same basic parts. For example, if you look at the forelimbs of different kinds of mammals, it is easy to see that each animal has one with a quite different shape, but they nonetheless share components. Despite their differences in shape and function, if you dissect these forelimbs, you can see that they include similar arrangements of bones, tendons, muscles and so forth.
These structures are different in each species, but they share sufficient similarities to appear as though they had been modified from some original common form. We refer to anatomical features having these kinds of similarities as homologues structures. These kinds of homologues structures could be best explained if living forms were not static, but instead had been transformed from some common form that was shared. That is, they are best explained by darwin and evolution.
An even more problematic case for immutability was the appearance of structures that had no apparent function at all, the so called vestigial organs or structures. An example of this might be the tiny pelvic bones that are still found in whales. If species were the result of a single perfect creation event, then why should such structures exist at all? A simpler explanation would be that species had changed over time in such a way that previously useful structures had lost their usefulness.
What About the Fossil Record?
Another sort of evidence that species were not immutable came from the branch of science we call paleontology today. Paleontologists are people who study fossils. In the early 1800’s, paleontologists began to describe fossils of species that were no longer living on the present day Earth. The existence of these fossils made it obvious that species weren’t constant.
There was another observation from the field of paleontology that was hard to explain away. It was obvious that some fossil species were similar enough in their anatomy to be related to living species, while at the same time differed enough to clearly have to be classified as a different species. It was possible to find series of fossil species occurring at different times in the fossil record which seemed to be connected, from one ancient form that looked one way, to one that existed today, with a number of intermediates in between. This was called the Law of Succession, and was consistent with the ideas of darwin and evolution.
These kinds of observations, coming from geology, comparative anatomy and paleontology were much discussed in the early part of the 19th century. Some scientists were beginning to suspect and even suggest in writing that species were not immutable. The idea that evolution might occur was beginning to be accepted. What was not at all clear was how evolution could occur. What would be a mechanism that could account for the evolutionary transformation of species?
Darwin’s main contribution, as it turns out, was not to suggest that evolution occurs, this was already out there. His real contribution was to understand the mechanism by which evolution could occur, which was embodied in his theory of natural selection. We'll see his theory in more detail in the next part of this article: Darwin and Evolution, Part 2.
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