hy could milk have provided strong favorable selection for l

hy could milk have provided strong favorable selection for lactase persistence?

Solution

ANSWER:

The lactose intolerant individuals cannot tolerate and thus metabolize the sugar - lactose in milk. This happens because of absence of an enzyme required for digestion of milk sugar i.e., the lactase enzyme in the digestive system. It is believed that drinking milk can provide a strong favorable selection for lactase persistence over generations. Drinking milk required the generation of lactase enzyme in the body to break down lactose. Over the generations, more and more people created the enzyme lactase. This is termed as the Niche construction. lactase production in body is maximum at the weaning period. However lactase persistance can make the individuals to express lactase throughout the adulthood, making them digest the lactose in fresh milk. Thus, the humans who started to drink milk gradually modified their pre-existing selection pressure leading to generating an evolutionary feedback responsible for developing an advantage in some of the individuals against others in certain environmental conditions. Lactase persistance is an adaptation to consume fresh milk without diarrhea and dehydration, beyond infancy. This is usually seeen in the LCT variant individuals who develope the trait to be more prevelant in population over time especially in the pastoralist societies. The practice of dairying in these cultures provided an environment in which the lactase persistence was advantageous due to the fact that they derived a major portion of nutrition their diet via fresh milk and dairy products whose lactose needed to be broken down into glucose and galactose for easy absorption in the body. This provided a selective advantage because milk which is a superfood, may have been a critical food source. Milk is rich in proteins and fats. Also, it is much safer to drink than water because of reduced exposure to pathogens.