I have been amazed how often I have to explain to people their jobs and the actual meaning of the rules they are enforcing on me.

And I mean people with advanced degrees. They are just tuned out and going through the motions on anything administrative.

When do different gene clusters emerge through selection pressure and when do they emerge at random? This question occurred to me throughout my reading of Wade’s book, and I did not find it clearly addressed. Perhaps the answer is well known, and I simply lack the relevant background knowledge.

I believe the answer is that random variation occurs when a particular set of alleles don’t have a big impact on fitness and reproduction. IE, whatever selection pressures exist, they are acting primarily along some other dimension than those affected by a set of alleles. In this instance, you get what I believe is referred to as genetic drift:

http://en.wikipedia.org/wiki/Genetic_drift#Genetic_drift_versus_natural_selection