answer:What evolution accounts for is the brain’s reward system. This is the feel-good mechanism that encourages us to do things that are beneficial to our survival, like eating, drinking and mating. This reward mechanism is based on the release of neurotransmitters, especially dopamine and serotonin, triggered by certain stimuli. We feel pleasure as a result, and so will want to repeat those activities. This confers an obvious survival benefit. Certain substances, though, can hijack this reward mechanism in various ways. Some mimic the effects of the neurotransmitters. Others artificially increase the release of the neurotransmitters. Alcohol does the latter, but also has the pernicious effect of decreasing the sensitivity of the receptors over time, so that naturally released neurotransmitters have a diminished effect. This causes the alcoholic to feel an increased need for the release provided by the alcohol. And because of the lower sensitivity, more and more alcohol will be required to provoke a release. So evolution simply put the mechanism in place. The chemical addiction exploits that mechanism.