How do environmental factors help determine which members of a species will survive or become extinct?

Natural selection

Explanation:

Whether or not an organism survives to reproduce depends on their surrounding environment. This is natural selection. Over time, that mutation can develop into a distinguishable adaptation and/or become more pronounced in a species since it increases the chances of survival.

Hope this helps:)

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."