CURSED TO A LIFE WITH NO CHEESE: HOW COME WE CAN DRINK MILK?

Ever wondered what cool sciencey stuff they are teaching undergraduates at the University of Queensland?
 Every school day I will post my newly learned cool fact... Enjoy

04/03/2013

EVOLUTION

CURSED TO A LIFE WITH NO CHEESE: HOW COME WE CAN DRINK MILK?

All baby mammals, (including humans) drink milk.

When we are born our mothers produce it and we drink it as a high energy disaccharide sugar filled growing juice.

 

After a while however, we move onto solids and the ability to drink milk fades. The enzyme in the intestine that digests the active disaccharide known as lactose, switches off production and after that, for almost every mammal, they can’t drink milk anymore.

The Lactose Molecule
A 'disaccharide sugar' full of energy

We know this to be what is called lactose intolerance and many adult humans are indeed cursed to a life with no cheese.

Imagine a world without cheese!

(If someone who is lactose intolerant does drink milk, the lactose left in their stomach is digested by bacteria and this leads to the feeling of being bloated and creating the potential of developing diarrhoea.)

However, strangely, some human adults retain the ability to produce the lactose digesting enzyme into their adulthood. Thus, keeping the flow of big glasses of milk and super-sized cheese pizzas unabated.

This is very strange as no other mammal has developed the ability to do this.

Furthermore, this ability is also not evenly distributed across the human population.

In Europe, West Asia, India and East Africa, there are high percentages of population that can drink milk. In other areas this percentage can be extremely low.

What’s going on here? Why do I love a big glass of milk so much?

 

This ability to drink milk evolved from the areas of the planet where access to milk products constitutes large portions of the diet. Evolutionary pressure has forced this ability upon our gut.

Interestingly, it seems that the ability to digest lactose has evolved independently across several ethnic groups, as these people share the trait, yet have had no common ancestor since the train arose. This insinuates that the genetic change required to switch on the enzymes production was not an extremely large change and the mutation was fairly common. Indeed, this is reinforced by the fact that in populations where milk consumption is extremely rare, you can still find around 10% of the population that can produce the enzyme.

Many people forget that humans are influences by evolution even today. Indeed, our bodies and evolutionary lineage will continue to be affected by its incredible power.