ntroduction lt is finals week on college campus and everybody is in the middle o
ID: 168833 • Letter: N
Question
ntroduction lt is finals week on college campus and everybody is in the middle of studying for exams, just waiting for summer break. Bjorn, Chris, Esiankiki, Xiao-Ma, Sanjeet and Linda are dying together in the international students dorm Bjorn: Hey, how are you doing with studying? I'm tired Chris: Me too. Let's take a break Icould alsa use some ice cream after that last final I bombed. Esiankiki: Did I hear ice-cream? I love ice-cream! Let's go downtown and find a spot. Is everybody coming? Let's go! Xiao-Ma: Hm, I can't tolerate dairy so I usually don't get ice cream or other milk products. Sorry guys, I'll stay behind Linda: What does that mean? Do you just not like milk I used to hate milk as a little kid. Xiao-Ma: No, I actually get really bad stomach cramps, bloating and diarrhea from milk. It's not pretty. My whole family is that way. When we were still living in China, it wasn't a big deal because we don't tradi tionally eat a lot of milk products there. Sanjeet: same for me 1 get the same thing and in India we don't eat a lot of dairy either, so it's not a problem if I eat Indian food. My mom gave me Lactaid though, so that helps me to eat ice-cream. Xiao-Ma, I can give you some. Let's go!Explanation / Answer
Introduction:
Lactose Intorace (LI) is a conditon in which people have symptoms due to decreased aility to digest lactose. Lactose is a sugar found in milk products.
Symptoms of lactose Intolerance:
Bloating, diarrhea, gas and nausea. These aymptoms start between 30 minutes to 2 hours ater drinking milk or eaing milk products. Severity of symptoms depends on the amount a person eats or drinks dairy products.
How LI occurs:
It is due to not enough of the enzyme lactase in the small intestine to breakdown lactose to glucose and galacotose. Although all mammalian infants drink their mother's milk humans are the only mammals that drink milk as adults. Because mother's milk is the only source of lactose in the life of a mammal. Once the mammal weans from breast milk, there is no need for it to have the ability to digest milk. So, it stops producing the lactase enzyme that digests lactose in the milk. Most people about 60% of Arican and Asian descendant stop producing lactase as they mature.
European descendant tend to retain the ability to produce the enzyme and drink milk throught life.
Coming back to the above graph, (the above graph in a table form, to make the comparison easier)
This shows that in East Asia almost all of them seems to be Lactose Intolerant. It is possible that as it is geogaphically far away from population that have Lactose tolerance there is no transfer of this partucular gene to East Asia population.
On the other hand there is a mixed trend in geographical regions (Middle east 1) that are close to population do and do not contain more number of people wiith lactose tolerance (Middle east 2, east aifrica). The same is seen in Northern Europe, Southern Europe and West Africa.
Countries that are away from the equator and far into the northern hemisphere ( Northern Europe) have lesser percentage of lactose intolerant population, while the countries near the tropics have the opposite trend.
There could be seeral reason for this pattern.
a) 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) Most adults 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.
c) We invented agriculture and along with it came the domestication of animals for meat and milk. This was the first time in mammalian history that a mammal had access to a dietary source of lactose other than breast milk. This eventually led some of us to develop lactose tolerance.
c) Milk became an important source of Calcium to some cultures of human population. Calcium is crucial for strong bones and to avoid diseases like rickets. Lactase persistence is an evolutionary advantage, and that's why some people developed this ability. It could be also because Asians and Aricans have enough sunlight to synthesize vitamin D, which in turn aids in the absorption of Calcium from dietary sources other than milk. So, they didn't have to evolve to digest milk. while the Europeans don't. so they have enough sunlight. On the other hand, Europeans have a greater need for a supplementary source of Calcium because they are more prone to vitamin D deficiency (due to lack of sunlight). That's why they eventually got rid of the lactose intolerance.
In conclusion it is possbile that the European descendant retained lactose tolerace ability and due to mgration of population the particular gene resposible for it was transfered to other populations.
Country/Region Lactose Tolerant (Black dots) Lactose Intolerant (Whte dots) Northern Europe 8 2 East Arica 7 3 Middle East 2 6 4 Souther Europe 3 7 Middle East 1 2 8 West Africa 1 9 East Asia 0 10Related Questions
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