How might the lack of genetic diversity found in populations of endangered species hinder their recovery?

Question

How might the lack of genetic diversity found in populations of endangered species hinder their recovery?

Answer 1

lack of genetic diversity would make a population susceptible to disease even a very benign one, also it would not allow the species the opportunity to evolve with there changing environment

Answer 2

Lack of diversity (even in machines) means vulnerability to a "common failure mode".  Biologically, this could mean a single disease or other environmental stress which would wipe out *all* the individuals.  

Low diversity:  Everyone is 5'5" tall, and a flood of 6' drowns everyone.

High diversity:  Pygmies and Watusi.  A flood kills some, but others survive.