Charles Darwin

When the name Charles Darwin is uttered, an immediate association brings about the concept of Evolution. Although he was not the first to discover this phenomenon, he was the first to explain it. In his book, The Origin of Species, Darwin discusses evolution- through variation, why it occurs, the struggle for existence, natural selection, the geological record, and several other topics. This book brought him great recognition as well as many violent attacks. It was written in a time in history when the people were very strong believers in the Church and God. Darwin was the first to contradict their religious beliefs of Creation, and was pummeled with criticism. Although today some still disagree, his explanation of evolution through natural selection is accepted by many. Darwin was just twenty-three when he began his journey aboard the H.M.S. Beagle. He traveled to South America and collected, observed, and noted everything he saw. During his travels, he found fossils of animals that looked like living animals, but were larger, different, and no longer on Earth. How could this be? According to Genesis, no plants or animals had changed since God had created them. If everything was exactly the same as it had always been, then how could extinction occur? Although this discovery went against the Church, Darwin could not ignore it. The more he observed, the more evidence he found; the Earth must have slowly and gradually changed since Creation, giving plants and animals time to adapt to the changes. He had just described evolution. Variation Within Species Over time Darwin observed many more clues that helped him somewhat understand the reasoning behind evolution. The Origin of Species begins with a discussion on variation. Darwin reflects on the diversity of older, cultivated species; they seem to differ much more than those in nature. He gives several examples of variation to illustrate this concept. Young from the same litter can be very different, as well as seedlings from the same fruit. He also goes on to explain the differences in pigeons. Of all the different breeds, there are extreme variations in beak size, skull shape, length of wings, and facial features such as eyelids. Another example was shown to Darwin by Mr. Lubbock. Darwin explains; I should never have expected that the branching of the main nerves close to the great central ganglion of an insect would have been variable in the same species; I should have expected that changes of this nature could have been effected only by slow degrees: yet quite recently Mr. Lubbock has shown a degree of variability in these main nerves in Coccus... Now that Darwin was sure that variations occur within species, he tried to explain why. He was exactly right in his reasoning, even despite the fact that he had no concept of the gene. Darwin thought that there are a number of causes, but in general the cause is the environment. Pertaining to cultivated plants, different climate, treatment, and excess food all will cause a variation from the parent that grew in nature. The conditions in which the parent grew were far different than that in which the cultivated plants would grow, and this, Darwin explains, is the cause of variation. However, he goes on to give several other possibilities that might cause variation. Reproduction is mentioned, for example the treatment of the ovules or pollen. In general, he believed that the conditions of life were responsible for variability. The Struggle for Existence, Natural Selection, Extinction The struggle for existence, according to Darwin, is due to the geometrical growth in which plants and animals increase. If more animals are produced than can survive (due to shortage of food, space, etc.), then there will be competition between and within species. Darwin uses man as an example. He states, Even slow-breeding man has doubled in twenty-five years, and at this rate, in a few thousand years, there would literally not be standing room for his progeny. So, there has to be a limiting factor on organisms that balances the system, and Darwin was right in thinking of the struggle for survival. He coined the term Natural Selection, and defines it as, The preservation of favorable variations and the rejection of injurious variations. This is a direct result of the struggle for existence. If there are too many animals in a particular area, for example, the ones that are the strongest or best adapted to that area (due to variations) will survive. There are different types of selection that need to be mentioned. Natural selection is the force that drives adaptive evolution, but there is a different type of selection that can occur- artificial selection. This is selection caused by man. We can manipulate a species grown under our care to produce particular traits that we find favorable to us, whether it be color of a flower, taste of a fruit, thickness of fur, or anything else we might prize. This is different from natural selection for one simple reason- it is not natural, it is forced. Natural selection through the divergence of character is a bit more complicated. It is possible that when a species has offspring they vary in one given character from the parents, and then their offspring vary in the same character but to a higher degree. Eventually, this separation into varieties can lead to breeds, and finally perhaps into species. This is considered divergence of character. Darwin uses an example of pigeon breeders who prefer opposite extremes in beak size. One prefers a short beak and the other prefers a long beak, and as the breeders continue to choose these extremes they will eventually lead to two distinct sub-breeds. These will then become their very own breeds that are different in character from each other as well as from their parents. And as time goes on, the animals with the intermediate characteristic will tend to disappear. Natural selection can also cause extinction in almost the same way. Species that produce numerous offspring will consequently produce more varieties, which may be favored at one time or another.