Lactase (LCT) gene is spatially limited along the anterior-posterior gut axis. The gene encodes for an enzyme known as lactase which is responsible for digesting lactose (the sugar of milk) into glucose and galactose. Lactose intolerance is the most common enzyme deficiency worldwide with the highest prevalence rates among the blacks from Native America, Asian America, and African roots. In contrast, races descended from northern Europe or from the northwestern Indian subcontinent have less chance to have lactose intolerance. This is thought to be an evolutionary advantage because people from northern Europe have a tradition to consume dairy products.