Although obesity is an unfavorable trait, there is evidence that in the past storing fat was quite beneficial. The body was apt to store fat to prepare for long periods of famine in our ancient history. This thrifty gene hypothesis was originally proposed by James Neel. Obesity leads to many health complications, one of the most common being Diabetes.
There are a high percentage of Native American populations that have Type 2 Diabetes. Unnatural Causes: Bad Sugar, a documentary, delves into the many ways that other factors have contributed to the genetic predisposition of Diabetes in the Pima Indian population of Arizona. Many of these factors happen to be political/economic issues. For instances, the Coolage dam diverted water from the Gila River (major water source in the Pima community) away from the reservation. The Pima Indians were left with little water resources for their crops and for survival, making them one of the poorest populations in America at the time. This severely affected the Pima economically and culturally. They had to learn to survive without water and adequate food. Many of the Pima died from starvation during this time of famine. Within 30 years of building the dam there were more than 500 cases of diabetes among the Pima Indians. This supports the thrifty genotype hypothesis. Their bodies were used to not receiving adequate nutrition so the body evolved to hold onto more fat than usual for survival. After a while the government provided food subsidies, but they were not healthy options. The Pima community did not have markets where fresh produce was abundant so they had to rely on processed food that had low nutritional value, provided by the American governemtn. This resulted in even higher rates of diabetes in the population today.
I think that the story of the Pima community in Arizona is a good example of our class discussion on how the human genome evolves simultaneously with our environment and culture. There is evidence that many minority groups, such as African Americans, that have experienced extreme hard ship in history have high rates of diabetes as well.
This study of the Pima community definitely peaked my interest, so much so, I did some additional research regarding this case study. I think this is such a fascinating case and the point you bring up about the ability of evolution to work in coordination with the environment and culture is evident. Furthermore, it makes me wonder of the time constraints within which evolution works. Considering the time it took for (according to this theory) this adaptation to occur, makes me consider now with once again changed conditions, how long it may be before the population may adapt once again to its change in diet? Further, would the adaptation be a complete return to the previous levels of storing fat now that diet has been restored for quite some time, or would it, long in the future, only “tweak” the change that has manifested only slightly?
Further, an article I read (link provided below) also studied a Mexican Pima community which were genetically the same as the Pima of Arizona, however they did not share the similar past and lack of nutrition. Of the 35 Mexican Pimas studied, only 3 had diabetes, and the population overall was not overweight. This provides an interesting experimental control to the case study of the Pima Indians of Arizona, and may lend to corroborate the theory posed by this article.
Link:
http://www.diabetes.niddk.nih.gov/DM/pubs/pima/obesity/obesity.htm
That article was very interesting! To answer your question, I think that it will be a long time before this population adapts to its environment. It has not nearly been long enough for the genome to match up to the current food sources available. Unfortunately, I also do not think that the quality of the food available to this Pima population will improve any time soon. Even higher rates of diabetes and other diseases will probably become evident in the future because of this.