Tuesday, March 16, 2010
Obesity and Evolution
According to statistics, about 58 million Americans are overweight. Needless to say, this is directly caused by consuming too many calories, especially fats (fats have twice as many calories/gram). However, some research suggests that human obesity may in fact be related to evolution. Why might have being overweight have been a selective advantage in the past? Is being overweight still a selective advantage today? To what extent does research show that being overweight is genetic? What are the risks of being overweight? Do you think the risks of being overweight will eventually lead to the natural selection of those who are not overweight?
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In the past, having extra weight meant having stores of extra energy. When food was scarce, individuals with these extra energy reserves were more likely to survive until the next meal (and then reproduce) than the skinnier individuals.
ReplyDeleteToday, with each meal right around the corner, being overweight is a disadvantage. Being overweight or obese lowers quality of life by causing lots of health problems, low self esteem, stress, and a stigma from society, all of which make it much more difficult to live.
Being overweight seems to be genetic, first because our overweight ancestors would've lived longer to reproduce and thus passed on more of their energy-storing genes. We also know that weight has a genetic basis just like height. Genes have a say in hormone and enzyme production, which both regulate the digestive system. However, just because being overweight is genetic doesn't necessarily mean that all overweight people are stuck. Weight has a lot to do with diet, lifestyle, and mindset. The ability to fight the urge to increase our energy stores is human and should be used to our greatest advantage.
In today's world, being overweight makes you less likely to find a mate and reproduce. It makes you more likely to die before reproduction from heart diseases, etc. So it seems natural to say that yes, natural selection will eventually eliminate genes that encourage a lot of fat storage. However, a recent study has found that slightly overweight individuals live longer than people in the normal range. Longer life does not imply higher quality life, but regardless, this survey suggests that some extra fat stores are still advantageous to humans, and if those humans live longer, they will have more opportunity to pass on their genes.
study on mortality: http://www.sciencedaily.com/releases/2009/06/090623133523.htm
http://www.newsweek.com/id/215115/page/2
Being overweight may have been a selective advantage in the past because our ancestors often went through periods where they weren't able to find adequate food, and having extra stores of food could be a selective advantage that allows a person to survive and reproduce. Our bodies naturally convert extra calories into fat since our ancestors were not always ensured to have food since they depended on foraging (not always predictable), which led to our ancestors bodies storing extra food consumed to help during time of starvation. Being overweight may also have been a selective advantage because it helped to cushion and insulate our ancestors’ bodies from cold condition. As thermoregulators, humans try to maintain a constant internal environment regardless of the outside environment. Having extra insulation would help to prevent heat loss, which would help to keep the body at a certain internal temperature.
ReplyDeleteBeing overweight is not a selective advantage as it once was. Humans in the majority of the world do not have to worry about not having enough food, making it not necessary to store extra fat since humans do not need to worry about times of little food. Humans today also do not have to worry about needing extra fat to keep warm due to the clothes and heating systems that keep humans warm despite the cold conditions in winter.
The risks of obesity include diseases and symptoms that are caused due to the large amount of fat in the body that prevent major organs from functioning properly. According to Omaha Medicine, obesity can often cause problems such as cancer, heart disease, high blood pressure, and diabetes. Referring to our unit on hormones, Type 2 diabetes occurs when either the pancreas does not make enough insulin or the insulin does not adequately target cells in the liver and body to take up glycogen in order to decrease blood sugar levels. Type 2 diabetes is often caused by obesity, and can even be treated through a healthy diet and weight loss.
Genetics have been shown to be part of the cause for obesity. According to BookRags, genetics play a role in the development of obesity by regulating how our bodies use the food we take in. The genes we inherited from our ancestors cause our body to store energy. With the unlimited supplies of food in society today, these genes and people's poor food decisions has led to the increase in obesity in society today.
I think the risks of obesity could lead to natural selection of those who are overweight in the next couple hundred of years. If obesity continues to cause so many problems, those who are overweight will be more likely to die from heart disease of obesity because there is no known cure for either of them. It also will become a selective advantage to be thin because people who are fit will be able to work more productively, allowing those people to potentially survive better due to their fitness level. This could lead to a decline in obesity because it prevents people from doing everyday things as efficiently.
Sources:
http://www.cdc.gov/Features/Obesity/
http://www.omahamedicine.com/health_risks_of_obesity.html