Sometimes, one of the most difficult aspects of getting people to understand evolutionary change is relating the basic ideas of adaptation and natural selection to humans.  Everyone gets the idea that artificial selection is responsible for our dogs and the food that we eat, but few understand that humans are bound by the same principles of natural selection and evolutionary change as all other living organisms.

A recent article coming out of the National Evolutionary Synthesis Center provides a fantastic example of how selection has favored a certain allele in individuals living in the high-elevation areas of Tibet. The study proposes that a small-subset of Tibetans has adapted to high-elevation living by producing less hemoglobin in their blood.

Normally, if a person moves to a higher altitude - their body responds by making more hemoglobin, which thickens the blood. For minor elevation changes, this does not present much of a problem. But for people that live at extreme elevations (some people in the Himalayas can live at elevations of over 13,000 feet, or close to 4,000 meters), this can present a number of health problems.

Since high hemoglobin levels would be a detriment to people at high elevations, it makes sense that natural selection would favor individuals that produced less hemoglobin at high elevations. Such is the case with the Tibetans in this study. Researchers have identified an allele of a gene that reduces hemoglobin production at high elevations. Comparisons between Tibetans at both high and low elevations strongly suggest that selection has played a role in the prevalence of the high-elevation allele.

The gene is  EPSA1, a gene on chromosome 2 (2p21  to be exact) that produces a transcription factor (TF). TFs act as regulators of gene expression, and the TF produced by EPSA1 is responsible (among other things) for regulating a series of other genes that are involved with oxygen use by the body, including the amount of hemoglobin present in the blood. The allele in the high-elevation Tibetans down-regulates production of hemoglobin, allowing these individuals to escape the consequences of thick blood.