One way to explain why gene frequencies change is that individuals with traits that are adaptive in an environment will stay alive to reproduce. Over generations their genes will become more common. This process describes:

evolution.
natural selection.
sociobiology.
heritability.
Would it be D?

3 answers

http://dictionary.reference.com/browse/heritability

http://dictionary.reference.com/browse/natural+selection
Thank you, changed my answer to B.
Good! :-)