Background information about Darwinian evolution, Primordial Earth and Dennett.
Includes information about Darwin's original theory of evolution by means of natural selection.
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Charles Darwin while he was aboard the HMS Beagle.
Charles Darwin saw evolution as the preservation of fitter species in the struggle for life. Evolution itself is propelled by the struggle for existence among all creatures. For instance, humans fight bacteria, viruses and themselves to survive. Each animal in the wild is both prey and predator. Plants fight drought and the conditions of Earth for survival. Every specie struggles for life. It is a fact of life.
If an ostrich had unusually long legs (due to a genetic mutation) allowing it to run faster, the ostrich would have an advantage over its peers. This slight advantage would allow the ostrich to find a mate (genes will be inherited) and food. Meanwhile, another mutated ostrich has shorter legs. Because of this disadvantage, the ostrich can't find a mate or food. This mutated ostrich dies and is not able to pass on the gene for shorter legs. Advantageous mutations favor the longevity of the mutated ostrich. Over many years, long-legged ostriches dominate the ostrich population.
Now, an uncharacteristically smart ostrich with short legs would also have an advantage again allowing it to reproduce and find food. So now we have two different kinds of ostriches. One kind has long legs and the other kind has short legs, but is more intelligent. These two species interbreed creating a long-legged intelligent ostrich. Evolution prevails. That is more or less how humans, over 4,600,000,000 years, evolved from the most basic microorganisms.
However convincing Darwin's theory was, many still found faults. For example, how did the first stirrings of life begin on Primordial Earth? How do you explain the many gaps between species? Other theories have been formed (attempting to answer these questions), but Darwin's theory will remain the most accepted.
In South America, Darwin observed the uncanny resemblance between the fossils of certain extinct armadillos and the skeletons of living armadillos. He observed only slight improvements. He would later see this as evidence of continuous descent with modification.
In the South American pampas, Darwin saw many different types of ostriches. Although they appeared to be quite similar, he noticed they were actually distinctly different. They were so different, the two differently developed species could no longer interbreed. Darwin later saw that these species were the result of one species migrating into two opposite directions. In the Galapagos Islands, Darwin observed many different species of finches. The finches were quite similar except in the shape of the beak. Each specie (of finch) had a distinctly different shaped beak according to the way the finch got food. This evidence proves that an animal must "fit" its environment and surroundings.
After visiting both the Cape Verde Islands off of Africa and the Galapagos Islands off South America, Darwin saw that there were far more differences between birds on the Cape Verde and the physically similar Galapagos Islands. The Cape Verde Islands' and the physically different Africa's birds were much more similar because they were geographically close. He saw this as another example of common descent. Geography had stopped the birds of Cape Verde islands from being similar to the Galapagos Islands. Perhaps after much migration, the birds of both island groups will be very similar.
Although Darwin had collected a substantial amount of evidence of evolution, he did not recognize that evolution had taken place until after some time. From the evidence that Darwin had gathered aboard the Beagle, he deducted that evolution definitely had taken place.
Two years after his return to London, Darwin proposed to the daughter of Josiah, Emma Wedgwood. He took advantage of the security of a happy marriage to work undisturbed on his revolutionary theory. Darwin already had a fairly clear picture of evolution prior to his proposal. A year before the marriage, he had secretly started the first of many notebooks on the evolution of species.
At this time, Darwin was infected with the Chagas disease. With this disease, he lived an undisturbed, quiet and rural life in the countryside. During this time, Darwin slowly pieced together all of the information he gathered aboard the Beagle. The result was two books, On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life and Descent of Man.