Answer to Question #171583 in Evolution for ashley

Question

• What was the disadvantage of the unfavored Human Lactose Intolerance trait(s)?
• How did the Human Lactose Intolerance numbers change after the environmental pressure?
• Were there other factors that helped Human Lactose Intolerance survive that were unrelated to genetics?

Answer 1

1.Prevents people from consuming milk and its derivatives.Hence this results in various levels of intolerance and the less lactase is synthesized, the more intense the symptoms of milk sugar consumption.

2.In adults, lactase (or lactase-phlorizin hydrolase) diminishes to approximately 10% of original levels in two-thirds to three-quarters of the human population

3.(a) Ancestral environment-people whose ancestors lived in very hot or very cold climates that couldn't support dairy herding or in places where deadly diseases of cattle were present before 1900, such as in Africa and many parts of Asia, do not have the ability to digest milk after infancy.The implication is that harsh climates and dangerous diseases negatively impact dairy herding and geographically restrict the availability of milk, and that humans have physiologically adapted to that.

(b)Early humans were hunter-gatherers that subsisted on wild plant and animal foods. The animal foods may have included meat and eggs but did not include milk because animals had not been domesticated. Therefore, beyond the weaning period, milk was not available for people to drink in early human populations. It makes good biological sense to stop synthesizing an enzyme that the body does not need. After a young child is weaned, it is a waste of materials and energy to keep producing lactase when milk is no longer likely to be consumed.