Darwin spent five years on his journey as the ship's naturalist on the H.M.S. Beagle. Some of the evidence he used to support his theory was based on fossils he saw in South America. In the 1800's, most people were of the belief that the world was only a few thousand years old and that organisms that existed were unchanged since the beginning. However, the fossil evidence that he found showed giant versions of modern animals that no longer existed. It pointed to the idea of an ancestor that may have changed over time to the modern life forms that exist today. He also noted that the most likely place that the life forms on the Galapagos Islands could have come from originally, was Equador which was about 600 miles away. Differences in environment, food supply, temperature, etc. would put different pressures on animals on each of the various islands. Over time, natural selection would favor those best adapted for their various environments and after two million years, you have many different species that have evolved from common ancestors in Equador. The most famous of course, are Darwin's finches. Also famous are the different giant tortoises that vary by shells, size and habits, from island to island. Other famous animals include iguanas. One is extremely unique, the marine iguana, which is the only marine iguana in the entire world.
The most famous example of evidence that Charles Darwin used to support his theory of natural selection is the example of the finches in the Galapagos Islands. These finches had evolved in ways that showed natural selection at work.
Basically, the finches were all descended from a common ancestor that had gotten stranded on the Galapagos, isolated from South America. Once there, they evolved to fill many ecological niches that were empty. This evolution could be found in the shapes of their beaks.
Each species of finch had evolved a new shape and size of beak. This beak shape and size was dependent on what sort of food this species had specialized in eating. This showed that the finches with the most adapted beaks for each kind of food succeeded and gradually ended up becoming new species.
THE THEORY OF NATURAL SELECTION
By Charles Darwin
Darwin stated that the process of natural selection was the basis for evolution.
Where as species is defined as a group of living things that are able to breed together and produce fertile offspring. Within a species there is variation between individuals.
Changes in the environment may affect some individuals and not others. Only those who can adapt to suit their new environment survive to breed and pass on their advantageous genes.
Other factors that tend to prevent all offspring surviving are:
- Competition for food
Eventually it seems that nature has decided which individuals has decided which individuals should survive and breed. There is a survival of the fittest.
Examples of Natural Selection:-
Example of environment causing changes in the species is the peppered moth. They live in woodlands on lichen-covered trees. There are two types of peppered moths:
- Light, speckled form
- Dark form
In the 1850's the dark type of moth was rare, but then pollution from factories caused blackening of trees, giving advantage to them as they were camouflaged. While the light moths used to live in cleaner areas as they had an advantage against predators, so it still survived to breed.
Darwin based his theories of evolution, including the theory of natural selection based on multiple sources of information including his personal observations, the geological theory of the British scientist Sir Charles Lyell, and the population theory of the British economist Thomas Robert Malthus. Many of his observations used as evidence for supporting the theory of natural selection were made by him as a member of a scientific expedition aboard the H.M.S. Beagle from 1831 to 1836. covering many places along the coast of South America. Darwin collected collected detailed information on many specimens of plants and animals during this expedition. Most significant among these observations were those made on the Galapagos Islands.
Darwin found striking differences between species on the islands and those on the mainland. He also found significant differences among species on each island. The study of data collected during the study convinced Darwin that modern species had evolved from a few earlier ones. Further the difference between the species on different islands and drew the attention of Darwin toward the role played by the environment and mobility on the development of new species. He arrived at an conclusion that species evolve as more and more favourable traits for a specific environment appear and are passed from generation to generation. He called this the process of natural selection.