Throughout most of his comparisons and case studies of natural selection in his book, Carroll avoids using humans as examples. He usually tends to focus on simpler organisms, but it seems slightly curious since his readers can much more easily identify with humans. However, the problem with using humans as examples to explain natural selection is our vast problem-solving abilities that we use to “outwit” evolution.
For example, lactose intolerance should be a grave selective disadvantage that would surely mean death for a toddler The toddler would have no way to obtain nutrition in the breast feeding stage of infancy from the mother due to the inability to digest lactose. However, through using formula and immunity boosting drugs this selective disadvantage has been circumvented, thus allowing what normally would have been a fatal mutation in the lactase gene to survive and be passed on into the human gene pool. This presents the ultimate irony in that human use of tools and resources to avoid selective pressures can be seen as “weakening” the human genome in the long run.
In a very detailed manner, explain at least 2 other cases in which humans have used technology or reasoning to avoid selective pressures from the environment. Also, give your opinion on whether you believe that human use of technology to circumvent natural selection is beneficial or damaging to the human species
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Argh, you posted this while I was typing up mine on the same issue!
ReplyDeleteWhat sets us apart from other animals is our brain. By inventing tools and weapons, ancient humans could hunt animals even without having evolved venom, strength, or speed. Back then and today, we are very dependent on tools for our survival, which means that we are becoming less and less dependent on our own bodies.
Agriculture and farming allowed us to grow all the food we needed without having to migrate. Not having to migrate meant that we could construct safe homes that protected us from predators and the elements.
A possible result of this is the fossilized MYH16 gene (p134), which makes our muscle fibers smaller than our primate relatives. I believe the human body will decay. Besides lactose intolerance, genetic/mental disorders and STDs are obviously not selective advantages, but we have found ways to preserve people with those conditions. By letting these disorders/diseases pass down, we really are hurting the gene pool by working against natural selection.
Like you said, Carroll obviously avoids using humans as examples for clear reasons. Humans have very unusual behavior compared to the rest of the biology world, but still are very genetically similar. Human intelligence and problem-solving abilities have huge effects on the rest of the world. Evolution and natural selection almost does not apply to humans because of our intelligence and problem-solving abilities. Our intelligence contradicts natural selection in many ways because of our morals. Humans don't live only to survive, but to pursue happiness and to contribute to society. Evolutionarily speaking, this is not a selective advantage because "bad" genes are being passed down at the same rate as the "good genes" therefore natural selection won't happen. Humans that are born blind are supported and fed by their families. In nature, an animal that is born blind will not be able to find food because of its inability to see, and will most likely die. A blind human will be able to survive because humans don't need to physically find their own food. There will always be food coming from their family or loved ones. Thus the blind human will be able to survive and reproduce, passing down the blindness to their children. One human behavior that can actually be beneficial to the human species is abortion. Although I personally don't believe abortion is moral, logically it could makes sense. If a parent can not financially or physically or mentally support a child, it is advantageous to be able to reverse a pregnancy. In a situation where giving birth would be fatal to both the mother and the child, it is beneficial to humanity to be able to at least save one life. But humans not only hinder natural selection within humans themselves, but we also hinder natural selection for the rest of the Earth. By constructing buildings and developing new technology, humans have effectively destroyed and contaminated countless ecosystems. Rain forests and coral reefs have been completely destroyed to deforestation and pollution. Humans have the effect of disrupting the processes of nature.
ReplyDeleteHumans usually use technology to outwit diseases that would otherwise kill the human with the disease.
ReplyDeleteOne example has to do with Type 1 diabetes mellitus. This autoimmune disorder involves the immune system attacking the cells of the pancreas (beta cells specifically) that produce insulin. The hormone insulin, in a non-diabetic, enhances absorption of glucose by body cells when blood glucose concentration rises after eating carbohydrates. Glucagon, insulin's antagonist, does the exact opposite. When blood glucose concentration is too low, the alpha cells of the pancreas release glucagon which causes the liver to break down glycogen (the stored form of glucose) and release glucose into the blood to raise the blood glucose level. In a diabetic, the beta cells of the pancreas cannot release insulin because the immune system sees these cells as foreign. Why the immune system attacks the beta cells is still unknown and researchers are working to figure that out. But the class I MHC molecule must not be exactly the same as the rest of the body cells' class I MHC molecule. Because the beta cells are "foreign", cytotoxic T cells will attack the beta cells as part of cell-mediated immunity. There have been many maneuvers that humans have "outwitted" type I diabetes mellitus. DNA technology allows humans to mass produce insulin by inserting an insulin gene in a bacterial chromosome and cloning the bacterial chromosome. Nowadays, diabetics can insert insulin using a needle or the newer insulin pumps. However, diabetics still are required to check blood glucose level on a regular basis (at least once before every meal). By inserting insulin into the blood stream, blood glucose concentration is lowered, so insulin is usually injected immediately after eating. A new study, reported on by Science Daily, talks about a new drug based on a chemical in garlic that can treat both strands of diabetes mellitus: type 1 and type 2. The drug contains vanadium and allixin and a study in Japan on diabetic mice successfully lowered blood glucose levels. (http://www.sciencedaily.com/releases/2008/11/081119084835.htm)
One very large controversial issue is stem cell research. Researchers truly believe that stem cell research could completely change the treatment for several human diseases. Leukemia is already using adult stem cell research through bone marrow transplants. Researchers hope to find cures and treatments for cancer, Parkinson's disease, spinal cord injuries, multiple sclerosis, and several other diseases. There are two types of stem cells being researched- embryonic stem cells and adult stem cells. Stem cells have the ability to cure several diseases because embryonic stem cells can differentiate into any type of cell. Adult stem cells can be used for repair. Recently, scientists at OU Cancer Institute have found a maneuver to select cancer stem cells in tumors and isolate the stem cells so the scientists can kill the cancer stem cells and prevent cancer from coming back. In this study, adult cancer stem cells are the focus to observe the stem cells' role in the beginnings of cancer, the growth and spread of cancer, and the coming back of cancer. (http://www.sciencedaily.com/releases/2008/09/080911140813.htm)
I personally believe that human use of technology to save people from otherwise dying of certain diseases is very beneficial. I suppose I am a bit bias, for my mother has type I diabetes mellitus and my grandma died of cancer. But if these diseases could be cured, it would be an absolute miracle.
Humans are working against natural selection or avoiding it as has been stated above. However, humans are using their intelligence for selection. Because of our human intelligence, our technology is beneficial to the human species. For example, Tay-Sachs is an autosomal recessive disease. Therefore, two perfectly normal people could get married and have children that have Tay-Sachs disease. This would be a result if both parents were carriers of the disease. With today’s technology this can be avoided and selected against. Often times in today’s world a couple will be genetically tested for a list of diseases before they get married or have children. The results would show the likelihood of the couple having a child with Tay-Sachs. The couple then could select against the disease by a few different ways. They could choose to adopt a child which would eliminate the chance of reproducing a child with that disadvantage. The couple could also use in vitro fertilization. In this situation the woman’s ova would be fertilized by the man’s sperm outside of the womb. This would allow for each zygote to be tested for the presence of Tay-Sachs. Then a zygote that was tested negatively for genetic diseases would be implanted into woman. This process allows for humans to select against “bad” mutations or genes that would be passed down in the offspring. This technology was beneficial for all involved and created more healthy humans. Therefore, I believe that our technologies are beneficial to the human species and still are creating humans that are “the fittest”.
ReplyDeleteBy circumventing the laws of nature through the use of technology, humans are ultimately harming the human race by sustaining the “bad” genes in the gene pool. For example, people with Cystic Fibrosis would never survive in today’s world without combinations of drugs and other treatments. By allowing people with Cystic Fibrosis to survive to maturity, it is endangering future generations. Without technological intervention, the Cystic Fibrosis gene would naturally be removed from the gene pool. Another example is juvenile diabetes. Like people with Cystic Fibrosis, people with juvenile diabetes would not be able to survive under normal conditions. However, with the use of technological advances such as insulin pumps, people with juvenile diabetes can live a full life. By allowing these people to introduce, the human race is dooming itself to generation after generation of sick people.
ReplyDeleteEvolution is based on the principle of natural selection. Natural selection is just that: natural. When humans intervene with diseases that would essentially remove “bad” genes from the gene pool, there is a possibility that we are plaguing future generations. In order to become a stronger race, humans need to allow natural selection to dictate the probability of passing on certain traits, not drugs. Ultimately, the use of technology to artificially evolve the human race could have either positive or negative effects. One outcome is the passing down of too many “bad” genes for the human race to survive adequately. Another outcome is the genes that cause certain diseases, which are seen as negative now, might be beneficial in other situations that might arise. For instance, both Cystic Fibrosis and sickle-cell anemia both prevent other diseases that were much worse at the time when these mutations first occurred. The best way to ensure survival is to allow natural selection to occur uninterrupted.
Humans have consistently been able to "outwit" evolution throughout history. For one example, we need not look very far. For many of us, it is, quite literally, right in front of our eyes. This human innovation is: glasses. While it may seem very simple, glasses are a way in which humans have outwitted natural selection. Normally, having poorer eyesight than normal individuals would definitely be a selective disadvantage. Therefore, if allowed to run its natural course, by conferring a selective advantage on full eyesight, evolution would eliminate individuals with poor eyesight. However, humans have invented glasses, which counteracts natural selection by eliminating the disadvantage in the first place. Glasses allow individuals with poor eyesight to see essentially with the same proficiency as people with perfect eyesight. Therefore, people with poor eyesight are no longer at a disadvantage, and they survive and reproduce normally. Therefore, glasses have been a tool with which humans have outwitted evolution.
ReplyDeleteA second human innovation which has combatted natural selection is the invention of the kidney dialysis machine. As we saw in the extremely riveting and entertaining video in Bio class, the dialysis machine filters the blood of individuals whose kidneys do not function properly. Normally, the kidneys are responsible for filtering wastes out of the blood. Without kidney function, nitrogenous waste would build up in the bloodstream and the individual would die. Normally, natural selection would eliminate individuals with dysfunctional kidneys, because those individuals would die before they had the chance to reproduce, and so they would not pass down their genes for dysfunctional kidneys. Thus, evolution would select for normal kidney function. however, the human innovation of the kidney dialysis machine enables people with dysfunctional kidneys to live, by artificially doing what the kidney normally does. The kidney dialysis machine has allowed humans to outwit natural selection by making it possible for people with dysfunctional kidneys, who would normally die, to live normally.
In a way, allowing undesirable genes to propagate themselves by impeding the natural course of evolution can be seen as weakening the human genome. However, I do not think this is true. What we must remember is that natural selection seeks to eliminate individuals who are at a disadvantage in their environment. with human innovation, certain undesirable traits are no longer a disadvantage. Take poor eyesight, for example. With glasses, an individual with poor eyesight can see just as well as a normal person. Therefore, with this human innovation, poor eyesight is no longer a disadvantage, as long as glasses are available. Since poor eyesight is not a disadvantage, it is not "weakening" the human race. If human innovation has made it so that a certain undesirable trait does not hinder an individual's chances of survival and reproduction, then we are not weakening the human genome. If anything, we are retaining more diversity in the human genome. Greater diversity means that should our environments change, we, as a species, would have a greater chance of adapting, as we would have a greater chance of some individuals being able to thrive in our new environment. We certainly do not want to advocate the course of ethnic cleansing.