Human Adaptation on the Tibetan Plateau 

Tibet is a mountainous region in Asia. Archaeologists believe people currently living in Tibet moved there from lower elevations about 3,000 years ago.  It is likely that when they first moved, they experienced the same changes to their bodies as people today do when they travel to the mountains: faster breathing and producing more blood cells to help them deliver more oxygen to their cells. 

Tibetans today have bigger blood vessels than people who live at lower elevations which allows their blood to circulate easier (there is variation of blood vessel size in the population). Although human bodies can produce more red blood cells when we travel from low to high elevations, we can’t make our blood vessels bigger. In Tibet, babies born to mothers with bigger blood vessels are more likely to survive than babies born to mothers with smaller blood vessels. 

The table below summarizes differences between people who travel to the mountains and Tibetans whose ancestors have lived in the mountains for thousands of years.

Using the information in the table about 

, construct an explanation for why, over many generations, the people of Tibet today are physiologically different from people living at lower elevations.

If conditions in Tibet remain stable for the next 1,000 years... 

I predict the proportion of Tibetans with big blood vessels will INCREASE/DECREASE (circle one) because: 

I predict the proportion of Tibetans with small blood vessels will INCREASE/DECREASE (circle one) because:

3. Recent scientific studies have documented variation in the alleles of Tibetan women. The alleles being studied are indicated as A and B below and represent alternative versions of a trait that affects oxygen content in the blood of the women.  High oxygen content is important for survival at high altitudes.  Describe two pieces of evidence from the table below that support the claim that allele B is affected by selection pressure.

4. What do you predict will happen to the relative frequency of Allele B in the population of Tibetan women over many generations?  Explain why and cite data from the table above as evidence.

Construct an explanation based on evidence for how natural selection leads to adaptation of populations.