In the 1800's the first theory of evolution was thought up by Jean-Baptiste Lamarck. He came up with a theory called spontaneous generation where species were continually being created from non living matter. Lamarck's theory on evolution was the traits of the parents that they gradually over time gained would be transfer to there offspring. For example if a adult dalmation had all black spots and and is tall and muscular from stretching and running a lot. Then its offspring would be tall muscular and have black spots. However this theory also has many flaws such as missing limbs scars or any other disfiguration were not passed onto the offspring. Lamarckism or inheritance of acquired characteristics was immediately discredited.
The next theory of evolution was proposed by Charles Darwin in 1858. On his voyage to the Galapagos islands he studied birds. Most notably a bird called a finch, he noticed different variations between the finches. For example a long skinny beak was meant for getting bugs out of trees, bigger wider beaks were made for crushing its food. Although for Darwin's theory to work four things must be present in the environment. Overpopulation, variation, competition and survival of the fittest. Once all the criteria are meet the species will start to adapt to there new environment by mutation in order to survive.
http://www.biology-online.org/2/11_natural_selection.htm
http://ts3.mm.bing.net/images/thumbnail.aspx
http://en.wikipedia.org/wiki/Darwin%27s_finches
Ritter, B., Burley, K., & Fraser, D. (2007). Chapter 5 Evolution. Nelson. (Original work published 2007)
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