To study the modern periodic table practical for class 9
Answers
Explanation:
Throughout human evolutionary history, breast feeding cessation typically occurred around the age of 2 or earlier. This meant that our digestive system no longer had the need for breaking down the milk sugar lactose as it was very rarely part of the paleo-/hunter-gatherer diet. To save energy producing a redundant protein our bodies stopped.
The lactase (LCT) gene responsible for producing the enzyme is alwats present in our cells but it stops being produced. Why? Because of something called the mini-chromosome maintenance complex six (MCM6) which initiates the production of lactase from the code in the DNA stops being produced around the age of 2. So no MCM6 means no lactase.
Knock knock, get the door, it's the agricultural revolution. Humans have reached completed the tutorial level of civilisation and have no domesticated animals. This means we have milk on tap, or on nipple, but tap has a better ring to it. The few people whose genetic code made a whoopsie doodle and kept producing lactase now had a huge advantage because they can drink milk (a highly nutritious drink full of sugar, fat, and water... and vitamins) without getting painful bloating or lethal diarrhoea. These lucky people are more likely to, you know, not die, and can make babies that are also able to drink milk and not die. Great!
One problem though...
The 'normal' gene that usually switches off lactase production is childhood is dominant meaning that most people in the world today are have primary lactose intolerance. This is because you need 2 recessive alleles from each parent, which is quite common in more western countries, but less common in eastern ones. And that's why European cuisine uses a lot of cheese, milk, and cream whereas Asian cuisine tends to avoid those ingredients.