Thursday, April 30, 2009

Ego, Disease, and Brawn: NetLogo Models of Ethnocentrism, Virus, and Muscles

Seeing as everyone seems to be so hyped up on the Swine Flu epidemic, Bommi, Kapeesh, and I decided to explore the Virus model. There are sliders for the number of people, the infectiousness of the virus, chance recovery rate, and the duration of the sickness. Following the extending the model instruction, we added sliders for the carrying capacity of the population as well as the average lifespan of the people in the model. Population density as determined by the people slider had a great effect on the contagiousness of the virus. When population density was really low, about 20, almost everyone remained healthy and eventually the infected person died and left the population disease free. When other variables remain the same, and population is increased to about 225, the population oscillates between a high level of infection and a low level of infection for the first 175 weeks. At this point, I was surprised to find that the levels of infected people, healthy people, and immune people eventually plateaued at stable rates; the number of healthy people being 1/5 that of the infected population. It is interesting to consider population density in the context of developing countries-- in particular India and parts of Africa like Zimbabwe--where the population density is extremely high and levels of infection are also high. The next step for me, if I were to continue to alter this model would be to add the variable of whether or not one knew of their viral condition, similar to the "getting tested" slider on the AIDS model.

We next looked at a model for muscle development...seeing as all of us are so naturally brawn rather than brain oriented. The most intriguing part of this model was the section that addressed the question of genetic ability that factors into the development of muscle fiber. One is born with a set number of slow-twitch muscle fibers and fast-twitch muscle fibers. Slow-twitch fibers allow for greater endurance whereas fast-twitch fibers allow for greater overall mass and strength. Consequently, when percentage of slow-twitch fibers is set at 90%, the level of intensity can be set high at 90% and the maximum interval of days between exercise is 5 days with 8 hours of sleep. The anabolic environment (green background, muscle building) is highest at this level however the muscle mass plateaus as shown by the relatively small diameter of red circles representing muscle fiber. Conversely, when slow-twitch fibers was set at 10%, the muscle mass was high but the intensity of the workout had to be lowered greatly in order to compensate for the individual's low endurance.

The Ethnocentrism model is essentially a model to represents the classic Prisoner's Dilemma using many more variables including the cost of giving, the gain of receiving, and the probability that an immigrant will cooperate with someone different from him or of the same background as him. Most variables create the expected results: if one raises the cost of giving, the number of people willing to cooperate drops quickly, whereas if one raises the gain of receiving, everyone starts cooperating. If the level of cooperation drops low enough--because either of these variables are at extremes--than the population will slowly start to die off. The most interesting variable in this model which I did not account for before was the mutation slider that changes the likelihood of mutation across generations. When mutation is low, as is the case with our current society, then populations will progressively become more segregated and cooperate only with those of their kind, or those who they can gain from. Cross-ethnicity cooperation is low. However, if you leave all the other variables untouched in the same conditions, and then raise the mutation rate, the population will become more and more integrated as offspring are not learning which groups to cooperate and defect from, but they must re-learn ethnocentrism anew.

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