I think a great component in the pleasure equation is our feelings. Almost all people that I have met with some kind of addiction had trouble distinguishing the rational from the emotional.
This relates directly to our evolutionary roots like you mentioned. Emotions are essentially instincts on steroids.
The emotional person fails to rationally bypass the present and is fearful either of the future ( anxiety) or the past (depression).
Very good point and I have found that I have been at my worst when it came to the drinking at periods when I was overly emotional. I have also come across people who use things like alcohol to counter overly rational tendencies - "come out of their shell" as the saying goes. As with most things there is a delicate balance that seems to be best.