Links
[1] https://www.hootsgo.org/?q=node/6329
[2] http://en.wikipedia.org/wiki/Natural_selection
[3] http://evolution.berkeley.edu/evolibrary/article/evo_25
[4] http://darwin200.christs.cam.ac.uk/pages/index.php?page_id=d3
[5] http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
[6] http://anthro.palomar.edu/evolve/evolve_2.htm