[eli_gottlieb]

>Another argument might be that nothing stops you or I from electing to abandon everything for the nearest crack den, either... except for the fact that we have learned, from interacting with our environment, that there are other things we enjoy, and that cocaine addiction might be more destructive than desirable over the timescale we're interested in.

Well actually, human beings have multiple conflicting reward systems. Reaching for the crack-pipe to wire up our dopaminergic circuit tends to result in driving our other reward chemistry to damn near zero.