An Historical Overview. (Please understand this is the short course - a lot is left out).
Notes below are based on the textbook Wallace, Sanders, and Ferl: Biology the Science of Life. 3rd edition. Harper Collins.
During the Voyage of the Beagle, Darwin found not a single rabbit in the pampas grass of Patagonia, South America. This startled him because, as a country boy, he knew rabbit country when he saw it. Instead he found a rodent called a Mara. Although Maras and rabbits are similar in appearance and behavior they belong to different groups of mammals.
You should list the similarities between the two animals.
Why are Maras (South America) and rabbits (North America and Europe) so similar?
Instead of dismissing this observation as "that's just the way it is", Darwin asked why are there no rabbits in South America. Perhaps he thought, because they can't swim across the Atlantic Ocean. Darwin also noticed that other rodents living in South America, appeared to be related to the Mara.
Darwin's ability to ask the right questions led him eventually to his theory of Natural Selection. The study of Biology makes little sense except in the light of evolution and the process of natural selection. In the words of Ernst Mayr, Darwin's theory "is quite rightly called the greatest unifying theory in biology."
During his seminal voyage, Darwin read Principles of Geology by his friend Charles Lyell. Lyell's book described the processes which could build and wear away mountains. Darwin's observation of a petrified pine forest interspersed with fossilized clam shells 8000 feet above sea level, could best be explained by the slow and inexorable forces described in Lyell's geology.
These geological processes, both men agreed, needed millions of years to take place. Darwin realized this vast time scale was necessary for evolution to take place.
The "Fixity of Species" seemed less and less likely, so Darwin's agile, questioning mind searched for another answer.
Once Darwin settled in after his voyage he began a 20 year process of developing and supporting his hypothesis that evolution (change) occurred because of natural selection.
He was convinced that evolution took place primarily because of:
- the fossil record including his own observations in South America.
- the enormous and unexpected variety of living organisms, especially beetles, previously unrecorded by naturalists.
- his observation of island biology, especially the adaptive radiation of finches seen in the Galapagos Islands only 60 miles away from the South American coastline.
- his observations of artificial selection -- human selection of plants and animals possessing traits which are of interest to the farmer or breeder.
- and Malthus's Essay on the Principle of Population, describing the explosive growth of populations quickly outstripping available resources, and finally reaching a natural balance in which only the fittest remain.
At some point Darwin realized that the environment, not simply random chance, could select those individuals from a variable population best able to survive and reproduce. This was the missing piece Darwin needed to develop his theory of natural selection which is based on the following 4 points.
- over population
- variation within a population
- competition for limited resources
- selection of those individuals most fit for their local environment
Darwin delayed publishing until a fellow naturalist, Alfred Wallace, wrote to him outlining a similar theory of natural selection. In 1859, the Origin of Species by Means of Natural Selection was published.
Modified June 5. 29, 2005