On the other hand, could the invention of alcohol allow for more far-reaching personality adaptations? By way of analogy, consider the theory proposed by both Jerry Pournelle and Temple Grandin: that the domestication of the dog allowed humans to offload to their canine companions much of the job of sophisticated smell cognition used in tracking game, thus freeing up valuable cubic centimeters of the brain for newer purposes.
Perhaps alcohol enables one individual to display a wider range of personalities than can be achieved through solely genetic means, thus allowing personalities to evolve farther in directions suitable for making a living, while still allowing people to display different traits in the evening.
What if the invention of alcohol allowed a single genome to exhibit different personalities at different times? Germans, say, could thus evolve personalities making them tend to be intense worrywarts, propelling their society into a model of technical competence. But who wants to be around other neurotics all the time? Yet, a couple of beers after work could allow the same Germans to turn into amiable, temporarily carefree companions, making social bonding more feasible.
Or the Japanese could evolve to be so intensely sensitive to the feelings of other Japanese that their culture becomes a byword for courtesy and politely vague conversations that don't hurt anybody's feelings or convey much explicit information. Yet, after a couple of shots of sake at one of their countless boys' nights out, the salaryman might suddenly feel free to tell his boss exactly how he's screwing up next year's sales forecast.
I presume this is just another evolutionary Just So story. But, it might be worth looking into through cross-cultural comparisons.