Friday, April 8, 2011
Fishy Disease
As Shubin describes on page 187, humans have many diseases that can affect our body and our lives, such as heart disease and diabetes. Why do humans develop so many diseases (such as heart disease and diabetes)? What does this have to do with our "inner fish"? Why is it that fish do not develop these diesases, whereas humans, who are a more advanced version of fish through many centuries of evolution, encounter these diseases a lot? What is different about the lifestyle of many humans at this point in time versus the lifestyle of a fish? How could these diseases be prevented? Any possibilities of using genetic engineering or other methods? Explain. Shreeraj Patel shreeraj.patel1@gmail.com
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Which comes as no surprise, Shubin provides an answer based in evolution as to why humans incur diesease like heart disease, diabetes, obesity, and stroke: we have "a body built for an active animal but the lifestyle of a spud" (Shubin 187), or in other words, our current structure was meant for a past function. For example, diabetes is disease with “a well-defined genetic basis,” yet seems to affect obese people more than those who are in shape, which led to James V. Neel’s theory of ‘A “Thrifty” Genotype” (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932342/?page=1). Essentially, he hypothesizes that our genes regulate the uses of our intake of food with a strategy that was more effective for the lifestyles humans used to lead. Hunters and gatherers went through long periods of time where food was not available—a ‘bust’ period, in which case storing food from a ‘boom’ period in the form of fat would have put humans at an evolutionary advantage. Our genes still force our bodies to act this way even though in 21st century middle-class America, there is plenty of food to go around and the boom-and-bust cycle no longer exists. On an interesting note, this previous lifestyle may why cupcakes and ice cream are so delicious; “they are high-value in terms of how much energy they contain, something that would have conferred a distinct advantage in our distant past” (Shubin 188).
ReplyDeleteAnother example of a disease in part caused by evolution in function, if you will, but remaining the same in structure is those associated with poor blood pressure. Humans were built with muscular, elastic arterial walls. As we learned from our circulation unit, the force of blood pumping exerted by the heart “against the elastic wall of the artery stretches the wall and the recoil of the arterial walls plays a critical role in maintaining blood pressure” (Campbell 907). There is more of this such pressure exerted during movement and exercise, which used to be an integral part of the day in the life of a human. Our sedentary lifestyle makes it more difficult for the heart to maintain blood pressure homeostasis. Additionally, “the contraction of skeletal muscles during exercise squeezes blood through the veins toward the heart”—a perfect diagram of this explanation is featured on page 909 of Campbell. Though the valves in veins prevent blood from moving backwards through the circulatory system, a lack of exercise can prevent the blood from moving ‘forwards’, or back towards the heart. Instead the blood pools around a part of the body and forms blood clots—a cause for heart disease.
Instead of complicated and expensive solutions like genetic engineering to cure these diseases, a simple, reasonable change in lifestyle with a less fatty diet and more exercise would probably be really helpful.
(Jackie Edelson, jedelson92@gmail.com)
Shubin (and Jackie) point out that our evolutionary ancestors were quite active creatures: "fish...were active predators in ancient oceans and streams" (186). Amphibians, reptiles, and even primates are very active in their search for food. Even when humans were hunter-gatherers, we were much more active than we are today. Our sedentary lifestyle, which Jackie points out, is the main evolutionary reason why humans today continue to die of heart disease and diabetes while our fish ancestors were free of these diseases. Our body was "built for an active animal" but today we maintain the "lifestyle of a spud" (187).
ReplyDeleteJames Neel addressed this issue from the perpective of our diet in his study, "Diabetes Mellitus: A 'Thrifty' Genotype
Rendered Detrimental by 'Progress?'" Basically, as Jackie mentioned, Neel suggests that our human ancestors were adapted for a boom-bust existence. As hunter-gatherers, humans used to experience periods of plenty and times of scarcity, causing them to feast and then eat considerably less in a cycle. This had its effect on our genes and illnesses today. Essentially, he proposes that our ancestors' bodies, in order to adapt to the boom-bust cycle, allowed them to save resources during times of plenty so as to use them during period of famine; thus, fat storage was essential to their survival. Part of the energy of the food we eat is used to support ongoing activities while some is stored, for example in fat, to be used later. It worked well back then, but today, in our world of rich foods, it fails miserably.
Jackie's point about high blood pressure is interesting: that the force of blood pumping exerted by the heart "against the elastic wall of the artery stretches the wall and recoil of the arterial walls plays a critical rold in maintaining blood pressure" (Campbell 907). However, although our sedentary lifestyle has made it harder to maintain a healthy blood pressure, one's diet and genetic factors must be considered as well. For example, a poor diet with lots of fats and a high intake of salt can affect the pressure of blood if these fats clog the arteries. Also, "approximately 30% of cases of essential hypertension are attributable to genetic factors. For example, in the United States, the incidence of high blood pressure is greater among African Americans than among Caucasians or Asians. Also, in individuals who have one or two parents with hypertension, high blood pressure is twice as common as in the general population" (http://www.medicinenet.com/high_blood_pressure/page4.htm). Though these genetic factors may indeed have arisen because of the human's more recent sedentary lifestyle, further genetic mutations may have happened in certain races, causing high blood pressure.
Like Jackie said, the simplest, most effective solution to heart disease and high blood pressure is a change in lifestyle, including a less fatty diet and being more active.
Hannah Kay (hgkay@aol.com)
As Shubin and both Jackie and Hannah states, humans did not have enough time to ‘adapt’ or ‘evolve’ to the lifestyle that we live in now, as our bodies are still made for the humans with hunter-gatherer lifestyle that lived some thousand years ago, or as Shubin states, “body built for an active animal but the lifestyle of a spud” (187). As humans continue with their high-calorie and high-fat diets, our body is not capable of adapting to the change, as it happens so fast. Therefore, the rate at which people who get diabetes, etc continues to rise with the increase calories in our diet; for example, even in the past three years, the people who have diabetes increased from 23.6 million in 2008 to nearly 26 million in 2011, a 9 percent increase (http://www.huffingtonpost.com/2011/01/26/diabetes-rates-in-america-_n_814432.html).
ReplyDeleteMr. Erdmann once told us this in our 2b/3 class, that the cardiac blood vessels were extremely thin in radius because before the high-calorie diet, humans did not need to have thick cardiac vessels, but now such characteristics are ending up as humans having cardiac arrests because the cardiac vessels are so thin, and little amount of LDL can clog up the vessels. No matter how advanced we are compared to the fish, we still cannot adapt to our high-calorie diet and because of this sudden change in environments, humans are suffering from these types of diseases, and “more than half of all human deaths in the United States are caused by cardiovascular diseases” (Campbell, 914).
As for the fish, their lifestyles do not change as fast as the humans’, except for the steadily increasing acidity in many lakes and oceans, which contribute in significant amount of the fish’s death. Aside from that, the fish’s diets do not increase significantly in calories and fats, so they do not have to worry about getting diseases such as heart failures, etc.
So in order for humans to prevent suffering from such diseases, all they have to do is ‘return to the past lifestyle’ and lower calories in their diets as well as having some exercise, so that our body can function properly to the right environment.
John Park (wisejsm@yahoo.com)