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.
The evolution of mental illness has always interested me, after our discussion in class about Schizophrenia, I became interested in the evolution of depression. Unlike Schizophrenia, depression is a common mental disorder, it is estimated to affect 121 million people all over the world and the number of people who have been diagnosed is increasing at a 20% rate per year. This phenomenon puzzles evolutionary biologists and psychiatrists because the alleles that are responsible for depression should be selected against over time according to the four postulates of evolution. This paradox is examined in this NYTimes article.
The proximate cause of depression is rumination, which means that people fixate on their flaws and problems, and extending their negative moods, rumination decrease a person’s functionality in daily life and it is considered useless, waste of mental energy. Rumination is associated with ventrolateral prefrontal cortex (VLPFC), which is located a few inches behind the forehead. Interestingly, VLPFC is also responsible for intense focus which is necessary to produce meaningful work. Therefore, it is hypothesized that depression has the benefit to allow the individual to have an increased brain activity that normal people cannot achieve. In another word, depression is an extreme end at the spectrum of ordinary thought process, and the inability to engage in pleasant activities help the depressed person focus better on their work
The question is, does depression and sadness indeed make people more productive for being more attentive? Psychiatrists and researchers has argued that many patients who have suffered from depression have a hard time performing daily functions such as bathe or eat, not to mention work and solve problems. These counter arguments suggest that the benefit theory of depression is a stretch.
Another school of psychiatrists suggest that depression could be a warning sign like chronic pain. Only by seeing a therapists and walk through the rumination process, can patients who suffer from depression find out the fundamental cause of depression.
This leads to the conclusion from the author which I think perfectly describes the relationship between emotions and consciousness, “ This is the paradox of evolution: even if our pain is useful, the urge to escape from the pain remains the most powerful instinct of all.”
The Greenspan paper sheds light on a topic that we have been focusing on since the beginning of class: how has modern medicine changed the evolution of human diseases? This author suggests that the development of modern medical technologies and vaccines has enabled human with rare diseases to live beyond reproductive age and pass on their genes; also, the improvement of living conditions has sustained tremendous population growth that gives rise to a larger gene pool that allows for possibilities of new mutations.Essentially, the cultural evolution has relaxed natural selection on humans.
By using the example of Cystic Fibrosis, the author provides evidence that survival rate for the once-lethal disease has dramatically increased over the years and patients with CF can easily live up to reproductive age. In addition, the author uses empirical evidence to support the idea that a small mutation could easily be magnified into deleterious conditions.
The authors distinguishes between culture evolution, which is the development of medical care and public health interventions; and biological evolution, which is the traditionally defined “survive of the fittest”. I think it is important to note that culture evolution is unique to human, so it is difficult to fit cultural evolution into the frame of traditional evolution theories. Also, I think the author brings up a great point that “personalized medicine” might be more challenging than we have expected due to the expanding population size and the weakened elimination on deleterious alleles.