Darwin's four postulates.
Ana Paula Ruiz
There are a lot of variation inside species and different characteristics per each species.
Ch1. Adaptation by Natural Selection. norton. Retrieved 4 April 2016, from http://www.wwnorton.com/college/anthro/bioanth/ch1/chap1.htm
Ch 3. Darwinian Natural Selection. Faculty Buffalo State. Retrieved 4 April 2016, from http://faculty.buffalostate.edu/penaloj/bio405/outline3.html
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