ring hard times, those individuals who were not lactose intolerant were better able to survive than those who were lactose intolerant. In times of marginal nutrition and caloric intakes, the edge went to those who could effectively consume dairy products. Of course, dairy products were not the only sources of food, but in some situations, the difference between surviving and dying could have been because of dairy products. Thus, through natural selection, people in dairying cultures became lactose tolerant. Cultures with little or no dairying, or those that used milk in different ways such as the making of cheese, had no reason to evolve toward lactose tolerance. Only in recent times has LI become a recognized world-wide problem, because of population movements, cultural changes with respect to diet, and food aid projects where milk products have been sent to susceptible populations. LI is currently a substantial world problem and will most likely continue to grow, particularly in the U.S. Increased LI in the U.S. is likely for a number of reasons (Houts 112). The percentage of northern Europeans in the U.S. is declining because non-northern European families tend to be larger than northern European families for cultural and religious reasons. Also, there is a large and continuing immigration into the U.S. from Asian and middle eastern countries and Mexico. The lactose tolerant population of the U.S. is decreasing because of intermarriages between lactose tolerant and intolerant populations. While not every marriage of a lactose tolerant and intolerant couple results in lactose intolerant offspring, there is ultimately a dilution of the lactose tolerant population. Since the median U.S. age is increasing, and LI seems to increase with age, there is likely to be increased LI. Furthermore, as nutritional education in this country improves, people are more likely to consume foods more equally from the four food groups. Since most Americans...
