Wednesday, April 8, 2009
Blind mole rats and senses
On page 126, Carroll discusses that the blind mole rat's lifestyle has caused evolution to create disproportional eyes that are covered with a layer of skin and fur, and the adaptations the blind mole rat has made in order to tell what time of day it is. Discuss how the mutation in the opsin gene has caused different lifestyles in animals (page 124). Also, if a human is blind (not because of evolution and their lifestyle, but by a random mutation or event) do their other senses work to tell the time of day (like the blind mole rat)? For example, is their sense of smell greater then those of a normal person? Also, Carroll mentions that our ancestors had a much greater sense of smell, what are some reasons this may be? What factors, do you believe, in our everyday lives will affect our future descendents?
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On page 126, Sean Carroll explains the mutations of opsin gene of Blind Mole rats. He explains that the rat has only two intact opsin genes, a red shifted MWS/LWS pigment that detects the light. Apparently this ability to detect light remains important because they need to run their biological clock according to the daylight.
ReplyDeleteIf a human is born with a random mutation that makes them completely blind, the natural selection will take care of him/her. The reason Blind mole rat can survive with such disgusting vision is that natural selection has prevented them to lose the ability to detect light.
It might be true that we lose vision or hearing, we may get stronger sense of smell or taste. For example, on page 140, Sean Carroll talks about the Howler monkeys who developed the color vision, and return, they lost the olfactory genes. Before we had the color vision, our ancestors had to rely on strong sense of smell to identify predators and surroundings. However, after the evolution of color vision, we were able to identify predators more easily, which degraded our strong sense of smell. It seems like if we gain something, we need to trade something for it.
We can see similar example from Blind mole rat. Because Blind mole rat has almost no vision at all, they spend most of their time underground. To survive underground, Blind mole rat has developed a cellular mechanism that helped them survive in Oxygen deprived environment. This fact has fascinated a lot of scientists because they believe that cancer cells use similar cellular mechanisms of blind more rat and scientists believe that Blind mole rat can be a ‘living Tumor’ that they can conduct experiments. As we can see, Blind mole rats have gained the ability to stay alive in Oxygen deprived environment in return of loss of vision.
I believe, our eating style will affect greatly on our descendents. Our food has become softer and softer and nowadays, we can get all kinds nutrients we need in just one cup. We wouldn’t need our teeth anymore very soon. There will be some point in our life when our descendents don’t have teeth and they will just drink all the nutrients. However, it will be the natural selection that will decide what will happen to our descendents.
Source: http://timesofindia.indiatimes.com/Health--Science/Blind-mole-rat-for-cancer-research/articleshow/4229833.cms
http://en.wikipedia.org/wiki/Blind_mole_rat
Sight is very important for some animals. All diurnal relatives of the owl monkey, for example, have an intact SWS opsin gene. But the owl monkeys themselves have a lifestyle of nocturnality which caused the relaxed selection on the SWS opsin gene. This gene became fossilized in response to its dark environment. Color sight is not needed for the owl monkeys to survive because they hunt during the night when there is very little light. Also slow lemurs which are nocturnal contain a fossilized SWS opsin gene as well. This shows that changes in the light environments that species live in correlate with the loss or decrease of color vision genes.
ReplyDeleteWhen a human is blind, they do not have improved other senses, but they do use their other senses more effectively to accommodate. In 2004, 2.4% of the world was visually impaired and 0.6% was blind. Studies have compared the threshold at which blind and sighted young people can identify smells. Rosenbluth, Grossman and Kaitz (2000), for example, found no in blinded and sighted children's ability to identify the different smells they were exposed to. The blind children did, however, give a wider range of labels to the smells, suggesting they paid more attention to smells. Another test was conducted to see how well participants (blind and sighted) were able to tell the direction a sound was coming from. In this test the blind children did perform better, but only marginally so. Again, this suggests blind children are making better use of their sense of hearing, not that their sense of hearing is ramped up to compensate for lack of sight. So blind people’s sense are not better, they just learn now to use them more effectively.
It is true that our ancestors had a much greater sense of smell than modern day humans. This is probably because of all of the technology we use that ended our reliance on hunting and gathering (which requires smell) to find food for survival. We have farmers and factories package up our food and put it in stores where we just buy it and then bring it home to eat. There is no requirement of smell to help us survive. The human sense of smell has turned into something “extra”. Yes it is true that you can smell food cooking, or smell it while you eat it, but does this help us survive or is it for enjoyment purposes? Technology will affect our future descendents also- maybe even to the point of not needing such an elaborate oligofactory system encoded into our genomes.
http://www.spring.org.uk/2008/02/blind-peoples-other-senses-not-more.php
http://www.blindawareness.com/spreadingtheword/blindmyth.php
This question is a very interesting one to ponder. It ties right in with having trichromatic color vision. In the blind mole rat, for example, the mutation in the opsin gene has caused the rats to become almost completely blind. The selection was relaxed on these rats and they therefore lost their vision. It is the whole principle of “use it or lose it”. According to an article, “The blind mole rat is the first animal found to navigate by combining dead reckoning with a sense of Earth's magnetic field, researchers say.” This means that because the rats have developed the ability to figure out which direction they are going by the earth’s magnetic field, they do not need the “blessing” of sight. On the other hand, “People and dogs can manage minor feats of dead reckoning, going in the right direction for at least a little ways in the dark, explains Tali Kimchi of Tel Aviv University in Israel. In mammals, this process, called path integration, relies on internal clues such as the sensations of walking. Bees and ants enhance path integration by reading the position of the sun. The blind mole rat (Spalax ehrenbergi), native to eastern Mediterranean regions, can't rely on the sun. It lives underground in elaborate tunnel networks” This is interesting because humans can sometimes feel their way around in the dark, but they can never go through life blind and completely fine. There needs to be some sort of aid to the blind.
ReplyDeleteAnother article maintains that these rats figure out where to sleep through use of their ability to sense magnetic fields. “We found that, under the earth’s natural magnetic field, the first group of mole rats exhibited a significant preference to build both their sleeping nest and their food store in the southern sector of the eight-armed maze. “ Mole rats do in fact have a different way of sensing their surroundings. They use nature because they live in tunnels and do not need to really see anything; they just need to use their other senses such as their sense of smell and their sense of hearing.
If a human is blind, I believe that their other senses do in fact get better over time. Many blind people are able to smell things that a person with relatively good vision would not be able to sense. According to an ABC article, “Fourteen-year-old Ben Underwood of Sacramento, Calif., is one of the few people known to use echolocation as a primary means of navigating the world on land. There's not even a hint of light reaching his brain. His eyes are artificial, but his brain has adapted to allow him to appraise his environment. He makes a "clicking" sound to communicate with objects and people around him.” This is interesting because it proves the fact that humans are able to modify their actions based on their senses. This boy who has absolutely no light reaching his brain is actually able to function in the world and get around without much of a problem. Therefore, yes, human senses do get better when one sense goes bad or disappears. Once again, according to the ABC article, “Scientists have discovered that in the brains of the blind, the visual cortex has not become useless, as they once believed. When blind people use another sense -- touch or hearing, for example -- to substitute for sight, the brain's visual cortex becomes active, even though no images reach it from the optic nerve. Echolocation creates its own images.” I find this very fascinating because the brain has indeed found use for the visual cortex and is able to make pictures out of something that it cannot fathom. This connects to the movie “Daredevil”. Ben Affleck is affected by a radioactive spill of some sort and he loses his sight. He promptly begins to hear and smell better. Although this is a movie, this is essentially what occurs in the everyday lives of blind individuals.
This article also discussed humans’ ability to smell. Apparently, humans have an extremely sensitive sense of smell. Although, when I read it, I immediately thought that this is impossible seeing as how Sean Carroll discussed the fact that humans’ sense of smell has deteriorated, the argument the author made was extremely compelling. The author describes the fact that even the faintest smell of something can remind us of our childhood or something else. Therefore, although scientifically our ability to smell things well has deteriorated, we still use that sense very much and rely on it in a plethora of ways. This proves that losing one’s vision is not the end of the world; there are other ways to sense our surroundings.
This ties into the biological theme of evolution. Humans have evolved over time. First, we had a weaker ability to see and now it has strengthened, while we had an extremely keen sense of smell and now that has diminished. This is important because humans will continue to evolve. At some point, humans may completely eliminate their need for a sense of smell because our vision may be powerful enough to not need it at all. These are all possibilities that can be discussed in great detail. According to an article, “Here's how some scientists think some eyes may have evolved: The simple light-sensitive spot on the skin of some ancestral creature gave it some tiny survival advantage, perhaps allowing it to evade a predator. Random changes then created a depression in the light-sensitive patch, a deepening pit that made "vision" a little sharper. At the same time, the pit's opening gradually narrowed, so light entered through a small aperture, like a pinhole camera.” This is important because we can see how vision in humans has changed over time and can analyze the importance of our ability to see a little more clearly.
http://www.highbeam.com/doc/1G1-113896711.html
http://www.google.com/search?q=blind+mole+rat+study&hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=J79&start=10&sa=N (second link – it’s a pdf of an experiment)
http://abcnews.go.com/primetime/Story?id=2283048&page=1
http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html