Darwin, evolutions and natural selection (Khan Academy article)
human-aided selection example (article)
Darwin's finches (video)
beaks and evolution (image)
overview (Nature article)
overview (Amoeba Sisters video)
overview (Khan Academy article)
cheetah example (NatGeo article)
example and overview (PBS article)
overview (video)
renewable vs nonrenewable resources (video)
sources of energy (PBS video series)
The Selfish Gene by Richard Dawkins (amazon used <$10)
Four Fish by Paul Greenberg (amazon used <$5)
The Biology of Skin (HHMI video)