New data in the January issue of The American Journal of Human Genetics suggest that the habits of your ancestors may have determined whether you can eat an ice cream sundae without experiencing the unpleasant side-effects of lactose intolerance.
Before fresh animal milk was readily available, humans did not need to be able to digest milk after they were weaned. However, the domestication of mammals approximately 9,000 years ago presented humans with the first opportunity to drink fresh milk throughout life. This provided a potential selective force for lactase persistence, whereby high levels of intestinal lactase, the enzyme that digests lactose, persist into adulthood. Individuals without significant levels of lactase are lactose intolerant, and the frequency of lactose tolerance varies between populations. Dr. Dallas Swallow and colleagues have examined the lactase gene in several human populations to learn more about its evolutionary history. They were able to determine the forces that shaped the lactase gene during two evolutionary periods, one before and one after fresh milk was available.
A significant event in human evolution was the movement of early humans from their roots in Africa to the rest of the world. Scientists estimate that this migration occurred before fresh animal milk was available to humans. Dr. Swallow compared the gene sequences of the lactase gene region between modern Africans and non-Africans in order to study the selective forces on the lactase gene during this time period. While African populations have high levels of genetic diversity at this locus, non-African populations show lower, and generally similar, levels of diversity. These results suggest that, as small populations moved away from the larger African population during this period, genetic diversity was lost in the migrating groups due to random fluctuations in the gene frequencies, termed genetic drift.
After early human populations separated to differe
Contact: Dr. Dallas Swallow
The American Journal of Human Genetics