This selection represents the first to our knowledge in which the blood level of a drug served as the selection index. Selection has commonly been employed by the drug abuse (particularly alcohol) research community, but the target of selection has always been either a behavioral response to or the amount of a drug consumed. We elected to target BEC rather than amount consumed because we were interested in developing an animal model of self-intoxication. We reasoned that there were many ways an animal might pattern its intake over a 4-hour test period, and not all of those would be consistent with behavioral intoxication at the end. Indeed, it might have been expected that by targeting high BEC, we would have been choosing those animals that drank more overall, and especially later during the session. However, Figure 3 shows that mice in the foundation population also tended to drink more in the second half of the 4-hour DID test and that the allocation of consumption changed only mildly over selected generations. HDID-1 mice are clearly drinking more overall. A more fine-grained
