Charles Darwin's Theory of Evolution by Natural Selection

Darwin collected and described thousands of animals and plants. In South America he observed the adaptations of organisms to a variety of habitat from jungle to grassland to mountain habitats. In the temperate regions the species resembled more closely the species of the tropical regions of South America rather than the corresponding species of the temperate regions of Europe. For example, in the grasslands of Argentina there are no rabbits, however, there are rodents that resemble rabbits; these rodents are unrelated to European rabbits but are similar to other rodents in South America. Moreover, the fossils in South America are dissimilar to European fossils but have similarities with extant (i.e. currently living) plants and animals in South America.

Darwin was particularly intrigued by the finches on the islands of Galapagos which are located approximately 500 miles from the mainland of South America. These finches, although unique to these islands, were clearly related to mainland species. There were 14 different species or genera of Galapagos Finch and their bills were adapted for particular diets. Darwin amassed these and other data including observations on variability in domestic animals (for example, dogs) which had been brought about by generations of selective breeding.

As well as drawing on his own observations, Darwin drew from the work of Linnaeus, Cuvier, Hutton, Lyell, Malthus and Lamarck. In the hierarchial classificatory system of Linnaeus there is a tacit acknowledgement of relatedness, for example, species belonging to one genus have more in common with each other than they do with species belonging to another genus. Linnaeus was a creationist -- as evidenced by his egotistical proclamation "God crea...

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...than available resources, and Lamarck who had proposed a theory of evolution based on a continuous process of gradual modification due to acquired characteristics.Both Darwin and Wallace brought together a multitude of facts including the geographical distribution of organisms, comparative morphology of living organisms and their fossil precursors. They postulated that long-term environmental changes including movementural selection.

Both Darwin's and Wallace's ideas presented to the Linnaean

Society of London.

1859 Darwin published The Origin of Species.

1865 Publication of Mendel's experiments on heredity

1871 Miescher isolated DNA

1892 Weisman demonstrated important role of nucleus in heredity

1900 Mendel's experiments rediscovered

1903 Sutton demonstrated chromosomes carry units of

Mendelian heredity

1943 Demonstration that DNA is the genetic material