http://www.des.ucdavis.edu/faculty/Richerson/RedNoise.pdf
This quote just about summarizes every post-apocalyptic movie I've ever seen.
"After this fixation of pure horizontal learning, occurring very approximately 12,000 time units from the start, the population completely loses most of its ability to track the environment, and, when the environment changes, mean fitness declines and the population drops (Fig. 2). When the population reaches very low levels, selection may return behavior towards the environmental optimum (as there are very few individuals in the population, and one who is incidentally blessed with suitable behavior, because of the error (σ) around the target behavior, can have many offspring and so change the mean behavior of the population)."