Chapter 11 includes many examples of diseases that show how humans are the product of a long and unique evolutionary history. Choose a disease and explain how it shows that we are influenced by earlier evolutionary traits. Eryk Fundakowski-
arthur2446@comcast.net
Obesity, specifically, is one disease that is the product of a long and unique evolutionary history. Shubin had talked about James Neel, who had claimed that the cycles of feast and famine in the past played a significant part in our genes and our illnesses (Shubin 187). Before humans were bombarded with an infinite supply of food, as many of us are now, the body had to find some way to conserve food and save resources -- this being fat storage. The energy of the food that was eaten was stored as fat so this energy could be used later on when food was no longer in supply. However now, with food being available at every corner, obesity has spread. Also, the sort of food that is being offered in many cases is extremely unhealthy (and this unhealthy food is extremely appealing to us). We love fatty foods because “they are high-value in terms of how much energy the contain, something that would have conferred a distinct advantage in our distant past” (Shubin 188). The more we eat, the fatter we grow, and eventually this fat is no longer harmless, but can become a serious problem: obesity. Obesity in itself can lead to hundreds of different health problems -- all of which lead back to the fat content in the body.
ReplyDeleteA lot of the time, obesity directly relates to heart problems. Obesity is associated with high triglycerides and decreased HDL cholesterol, which can lead to high blood pressure and a heart attack. Because those that are obese are most commonly seen on a high-fat diet, their level of exercise is severely decreased (contrary to how it was in the past) and with fatty foods comes high blood pressure (http://www.annecollins.com/obesity/risks-of-obesity.htm).
Luckily, however, there are several mechanisms our body has to regulate body weight. This has probably been a more recent adaptation because before, malnutrition was a larger problem than over nourishment. “Operating as feedback circuits, these mechanisms control the storage and metabolism of fat. Several hormones regulate long-term and short-term appetite by affecting a ‘satiety center’ in the brain” (Campbell 894). The idea that before, it was a selective advantage to be able to store fat, and now there are mechanisms in the body to control weight gain is contradictory, but clearly defines the continuously changing world undergoing a constant process of evolution.
-Michelle Layvant, michellel94@hotmail.com
With respect to obesity, “In the research report, scientists show that human evolution leading to the loss of function in a gene called "CMAH" may make humans more prone to obesity and diabetes than other mammals” (http://www.sciencedaily.com/releases/2011/02/110224145647.htm). These researchers beleive that humans developed this condition over time due to their high fat diets. These diets led to the loss of CMAH which contributes in creating insulin-producing beta cells. If there are no pancreatic beta cells, it can cause type 2 diabetes. I really like your explanation and examples as well but I think that we could focus on an even more common occurence, hiccups.
ReplyDeleteShubin says that hiccups have its roots in the history that humans share with tadpoles and fish. Hiccups is another annoyances we have that can be explain through evolution. Hiccups is caused by a spasm of muscles in the throat and chest. This is an involuntary response which means we cannot control it. Hiccups are triggered when we eat too fast or eat too much and in some cases are caused by a tumor in the chest.
Hiccups occur because we inherited anatomical features from two different animals on the tree of life. The fish is one and the amphibian is the other. We inherited the major nerves that control our breathing from fish and the hiccup itself was inherited from the past we shared with tadpoles. There is a group of nerves called the “phrenic nerves” that supply the diaphragm. The problem is that these nerves originate from the base of the skull and have to go through a series of twists and turns to make their way through the chest cavity and eventually end in the diaphragm just below the lungs. There are a few structures along the way that can press on these nerves and irritate them thus interfering with our ability to breathe. A hiccup is the end result of this irritation. A better design would have been for the nerves to originate from an area on the spinal cord much closer to the diaphragm.
We inherited this design from fish with their gills closer to the neck. There is evidence of gills present in us when we are embryos that support this idea but they gradually disappear as we grow into a fetus as the diaphragm develops to control our breathing. So as we develop into a fetus the origin of the nerves do not change, therefore the nerves must now travel further since the diaphragm is far removed from the neck.
-Adnan Jahan
(adnanjahan@gmail.com)
continued...
ReplyDeleteThe other reason we may have hiccups because we inherited it from the tadpole.Some animals start their lives in water such as amphibians, specifically tadpoles, breathe with gills and lungs. They are able to do this because they have the right muscular structures and placement of nerves to produce hiccups naturally. The tadpoles must take in water and push it out through their gills for oxygen but at the same time they must keep the water from entering their lungs. They do this by closing the glottis, a flap of tissue over the opening to the lungs, to close off the breathing tube to the lung while they are drawing the water in to push it out through the gills. Basically, what they are doing is a prolonged hiccup. Ours is much shorter. By the way that same flap of tissue that close our bronchial tubes is called the epiglottis.
Researchers in France believe that there is a link to evolution with hiccups. This theory beleives that hiccuping originates from a group of animals who have combined the closure of glottis and the contraction of muscles for breathing does serve a purpose.
“They are the primitive air breathers, such as lungfish, gar and many amphibians that still possess gills. These creatures push water across their gills by squeezing their mouth cavity while closing the glottis to stop water getting into their lungs. The researchers believe the brain circuitry controlling gill ventilation has persisted into modern mammals, including humans.” They have found many similarities between gill ventilation and hiccuping through its use in tadpoles. Both are inhibited when the lungs are inflated but there is obviously a reason or advantage that these animals have kept this mechanism 370 million years after evolving and moving on to land.
There are some new findings however on what the use of this mechanism may be today. “Straus and his colleagues suspect the habit has been adapted to a new use - helping mammals learn to suckle. The sequence of movements during suckling is similar to hiccuping, with the glottis closing to prevent milk entering the lungs.” (http://news.bbc.co.uk/2/hi/health/2730251.stm).
-Adnan Jahan
(adnanjahan@gmail.com)
Michelle brings up a good point in discussing the adaptation of our species over time as “rich foods” became more common and malnourishment less common. Obesity, according to Michelle, has modified and affected our ability to control body weight and store fat. Although obesity has become more common as a disease, Adnan focused on a condition that we all experience – hiccups. It was interesting to hear about Adnan’s research in regards to our evolutionary development as far as hiccups go because they are not normally seen as a “disease”. Many people generalize the term “disease” to a rare, genetic condition that causes one to be bed-ridden or seriously ill. However, disease is defined as “an impairment of health or a condition of abnormal functioning” (WordNetWeb, Princeton.Edu). Hiccups, therefore, does fall into this category contrary to what we would expect. Caused by muscles in our diaphragm, they have become a regular part of all of our lives because of traits that we have inherited such as the position of the diaphragm and our fetal gills from fish and amphibians. Another disease to delve into is hernia.
ReplyDeleteA hernia occurs when a rupture in the abdominal wall causes the inner abdominal contents within the wall to protrude outside of it, causing a physical bulge. This then, when large enough, may cause the contents to literally fall out of the abdominal wall when standing and fall back in when sitting. These hernias are usually present since birth and enlarge over a lifetime. When the abdominal contents are too great to fall back in the hole, surgery is necessary to save the patient’s life because the escaped abdominal content could block blood flow (“Disease of the Abdomen-Hernia”, After50Health). Inguinal hernias occur in males where “intra-abdominal fat…bulges through a weak area in the lower abdominal muscles…occurs near the groin” (“Inguinal Hernias”, National Digestive Diseases Information Clearinghouse). This occurs from the descent of gonads in males that results in a weak area of the body wall (Shubin, 195). However, to understand the process of this, we must look at those that we have inherited these traits from – the fish.
Sonia Doshi (soniadoshi7@gmail.com)
(con't)
ReplyDeleteAccording to Shubin, our aptitude to develop hernia had arisen from the structure of fish (Shubin, 193). Fish have gonads that are near their chest and heart whereas we would not be able to properly reproduce or maintain bodily temperatures for sperm if they resided near the heart or deep in the chest. The sac that the sperm “lives” in the scrotum whose muscles contract or expand to adjust to the temperature. Shubin explains that this optimizes healthy sperm production (193). Our gonads develop in the same place as fish, near the liver, but the path that the sperm take varies. As Shubin had explained, the sperm travels from the scrotum, through the sperm cord, up toward the waist, over the pelvis, through the pelvis, through the penis, and out (195). When the “gut travels with the testes”, inguinal hernias develop (195). One aspect to take into consideration is that fish fertilize externally while mammals fertilize internally. This causes a difference in the pathway of our gonads. However, overtime, as internal fertilization had allowed this change in pathway to adapt to the process of reproduction in mammals (Campbell, 1000). Our structure, as compared to fish, varies and, therefore, in order for our sperm to thrive, their path of travel must take a certain route and their temperature must be maintained. Therefore, there position could not stay near the chest or heart as it is in fish. This has been an adaptation from the sperm pathway of the fish. However, mammalians that walk on four legs, are les likely to develop inguinal hernias because their groin structures are not stretched or under tension, and the inguinal canal ruins in an upward direction (“Groin Hernias”, Abdominal Wall Hernias). In bipedal mammals such as humans, the abdominal contents are weighted downward causing gravitational stress on the lower abdominal wall, leading to the more frequent groin hernias (“Groin Hernias”, Abdominal Wall Hernias). In females, however, the abdominal wall muscles are much stronger because their reproductive process forces their abdominal wall to undergo a lot of stress during childbirth (Shubin, 196). Therefore, they are less likely to get a hernia. These adaptations are evident in observing the fish structures and comparing them to our own structures.
Sonia Doshi (soniadoshi7@gmail.com)
This comment has been removed by the author.
ReplyDeleteMany scientists state that the mutations in our evolutionary past caused us to be succeptible or immune to certain diseases. According to researcher Dr. Dan Mishmar, a molecular biologist from the Department of Life Sciences at BGU, "Our ancestors responded to environmental changes, such as climate shift, with mutations that increased their chances of survival. But today, these same mutations predispose us toward complex diseases such as cancer."
ReplyDeleteTo prove this hypothesis, he tested the genome mitochondria mutations from 98 unrelated individuals. Combinations of mutations tended to occur in tumors in precisely the same DNA building blocks that changed during evolution. It was also found that the mitochondrial genome of humans who migrated out of Africa to Europe 100,000 years ago carried several mutations found in almost all of today's Europeans. The mutations are already part of the population and have had a survival function. When these same mutations reoccur in the correct environment, they can cause disease. Overall, Dr. Dan Mishmar's hypothesis was proven correct as the same principles that drive evolution toward the emergence of new species govern the emergence of diseases.
I found this very interesting chart which shows human evolution tradeoffs. It answers the question asked above by giving many examples.
(http://online.wsj.com/article/SB10001424052748704454304575081613327728110.html)
This includes examples not listed in the chart such as the various recent mutations developed in response to infectious diseases, particularly as people started living in large communities. For example in Africa, some 25 new gene variations and an entire blood type have emerged to help people resist malaria in the past 10,000 years. About 10% of people in Europe today have a gene variation that makes them resistant to HIV/AIDS. Human evolution as a response to certain diseases proves that we are presently influenced by evolutionary traits that may go unnoticed.
Eryk Fundakowski- arthur2446@comcast.net
http://online.wsj.com/article/SB10001424052748704454304575081613327728110.html
http://www.physorg.com/
http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ISSUEID_CHAR=95C97E8D-4E3A-4EE5-A478-944FC3A850A&ARTICLEID_CHAR=A4B3D340-548B-4EC1-A25A-D7872DABCB6