Tuesday, March 22, 2011
Beyond the Tooth
In chapter 4, "Teeth Everywhere," Shubin extensively discusses the evolution of specialized teeth. He describes how teeth over time became evolved to meet the changing diet of evolving organisms. The teeth of humans and other organisms are "extra hard," Shubin concludes, because "teeth have to be harder than the bits of food they break down," (Shubin 74). Human teeth are capable of handling the varied diet that we consume today, but what other body systems/parts have adapted to meet the demands of human nutrition? What aspects of the human diet caused changes in the digestive system of humans? How do those changes give humans a selective advantage?
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The teeth of humans, compared to other organisms, are very specialized and detailed in order to fend for the well-ranging diet of humans. There are three types of human teeth that specialize in different parts of the mechanical breakdown of food that happens in the mouth, and the upper and lower teeth are made to fit perfectly with each other. But teeth aren't the only body parts that have adapted to human's diets: many specific organs of the digestive system have also had to adapt to meet the nutritional needs of the human diet, and the digestive system of humans as a whole is very complex and specific compared to many other animals.
ReplyDeleteIn terms of the digestive system as a whole, evolution of the digestive system from small fish (over millions of years ago) to humans today has led to a very specified digestive system with many parts and organs, as well as hormones and proteins/enzymes that are involved with digesting food so that it is done in an efficient and effective manner.
One specific part of the digestive system that has been a very important adaptation to meet the demands of human nutrition is the stomach and its acidity. The concentration of HCl is very high and the pH of the stomach is at a level of 2. Because of this very acidic environment, any bacteria that enters the body with food is killed and the extracellular matrix that binds the cells of meat and plant material together are disrupted, therefore making them easier to digest. This is a very important adaptation since the human diet today is very meat and vegetable heavy.
Another very important organ that is involved with the digestive system is the liver, which has adapted to meet the needs of the high-fat diet of humans today. The liver is responsible for producing bile (which contains bile salts) that act as emulsifiers to help digest fats and lipids. This adaptation of the human digestive system is very important because the foods humans consume today are often very high in fat and the human body needs to able to digest this fat as effectively as possible. Another very important function of the liver is its ability to break down toxins, such as alcohol, and help balance nutrient utilization. Since alcohol is a poison to the human body, the function of the liver to digest this alcohol and filter it out to make sure other bodily functions and organs are not damaged is very important. The liver also plays a vital role in balancing and maintaining the humans ability to utilize the nutrients consumed by food effectively. This is very important in order to meet the needs of nutrition of humans.
Some aspects of the human diet that have caused changes in the digestive system of humans is the high consumption of alcohol and fatty foods that are very popular today. Because humans have been eating more and more junk/fast foods and alcohol has become a very common beverage amongst many people, the liver especially has had to change in order to meet the demanding needs of more effective and efficient alcohol/fat digestion. Since the liver is able to adapt to these specific changes in the human diet that are occurring constantly, this feature itself gives humans a selective advantage. This is because the whole body itself is able to change according to the ever evolving diet of humans.
Sujin Ko (sujinko93@gmail.com)
Sources: Campbell - Chapter 41 pages 886-888
http://www.elmhurst.edu/~chm/vchembook/642alcoholmet.html
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ReplyDeleteIn addition to the parts of the digestive system that Sujin mentioned, it is also valuable to realize how the evolution human nutrition and the digestive system has influenced evolution of the brain. It is interesting that as brain size has increased through evolution, human energy needs have increased (Milton). The brain and digestive system are two of the most energy demanding organs of the body. Therefore, as the human diet became richer in fatty foods, the metabolic rate could have increased, increasing the size of the brain and the human body. Over time, as our brains have evolved and become larger, our diets have evolved to include more nutritious and fatty foods. This change in diet and metabolic rate could help explain how through evolution, humans have gradually become taller and heavier (Kleiber).
ReplyDeleteTo elaborate on what Sujin said about enzymes evolving to aid in digesting more complex foods, many pancreatic enzymes have evolved for this purpose. For example, pancreatic trypsin and chymotrypsin aid in digestion of proteins by cleaving amino acid bonds (Campbell). These enzymes likely evolved in humans as human diets became higher in protein, which probably occurred as a result of humans eating meat. Another enzyme, pancreatic lipase, aids in the digestion of fat (Campbell). This enzyme probably evolved in humans as our diets became higher in fat. This probably happened when new technology that could make food faster with the use of engineering became popular. The evolution of these enzymes show how the digestive system has adapted to the changed diets of humans. Having these enzymes and digestive capabilities gives humans a selective advantage because it allows us to eat foods with more nutrients which allows us to grow and develop more.
Sources:
AP Biology- Campbell/Reece
http://www.beyondveg.com/billings-t/comp-anat/comp-anat-4a.shtml
Marissa Lobl (marissa.lobl@gmail.com)