Explaining exceptions to Dollo’s Law

Explaining exceptions to Dollo’s Law Explaining exceptions to Dollo’s Law a review of the concepts of constraint and contingency. In 1890 Louis Dollo a Belgian palaeontologist, came up with the theory that evolution is irreversible, expanding on the work of Edgar Quinet, a historian who had first pondered this theory (Chopra Rogers, 2013) . Thus explaining that the constraint of evolution that it is irreversible and if certain traits are lost this effects the contingency of evolution, thus past changes having an effect on the present and future of the species, this could by chance may or may not have an effect on the re-evolution of certain traits. The theory states that evolution is irreversible because of the structures and functions lost in the line of evolution cannot return in the lineages that they were once lost in e.g tails in our monkey like ancestors. This therefore suggests that genes formally required to code for adaptive traits during selection pressures will become non-functional when selection pressure is low or non-existent (Marshall, et al., 1994). The repercussions of this are that any trait coded by these genes will be lost forever and cannot ever occur again in the same lineage according to Dollo’s law (Marshall, et al., 1994). In recent times many papers have been published that have disputed this law. There has been some work done on seeing if the constraints of evolution hinder further adaptation and whether this can either facilitate or hinder the re-emergence of the original/ancestral trait (Yedid et al. 2008). This essay will look at some of the cases where this law potentially does not apply and discuss how relevant Dollo’s law is in biology, and if it is relevant at which point does the law either become to ambiguous or too specific. We will discuss Dollo’s law at two different bases; the Genetic and Morphological. Under Dollo’s law the genetic basis of this is that if a gene is lost due to natural selection and bred out of a population, the trait coded by the gene is lost and cannot be regained in the same lineage over evolutionary time. A Study to test the genetics of Dollo’s law was tested on the genome coding for the sex combs in Drosophila bipectinata and its close relative Drosophila malerkotliana (Seher, et al., 2012). The study found that some the genes that code for sex comb may alter the structures dramatically (even in a single inversion) and some that had multiple inversions of the chromosomal structure which had no difference in the sex comb morphology. They then suggested that Dollo’s law should follow molecular pathways rather than just the genes that code for them. This is due to many genes being regulatory genes, which can sometimes when activated; open up many pathways to code for different cellular processes. This can then have an effect in gene expressio n and therefore a trait previously lost in evolutionary time is now being expressed due to these â€Å"nexus† regulatory genes (Seher, et al., 2012). The can be demonstrated in another experiment where mouse inductive signals that gave rise to stem cells providing teeth, where cultured with graphs of chick oral dermis. The result found that the Chicks oral tissue actually started to form enamel organs and even in some case small malformed teeth (Marshall, et al., 1994). In a review published by Bull Charnov it says that In relation to irreversibility there are two generalisation from there analysis. 1) â€Å"selection of intermediate phenotypes is critical to evolutionary transitions whenever the two phenotypes are so different that multiple mutations are required to change from one to another† (Bull Charnov, 1985) , and 2) â€Å"a second principle common to several examples is that the genome may progressively accommodate a character state the loner it is maintaine d† (Bull Charnov, 1985). These two generalities the summary was that irreversible evolution is founded on the dependence of the biological details of the system, with some more general rules that apply at a much less focused level. The constraints with looking at the genetic level are that we are looking literally â€Å"under the microscope† and it is fine picking each detail of gene selection and deletion and applying this to Dollo’s law. But as said before genes can take many pathways due to nexes regulatory genes, so who is to say that a feature i.e. eyes lost in a cave fish (speaking hypothetically) came back in a recent form but using different genes to cause the eye. Is this against Dollo’s law? Or because of the different genetic pathway it is just a natural progression in evolution. Using morphology as a basis with regards to Dollo’s law it states that any morphological trait that is lost in a lineage cannot ever be re-expressed for example the hind legs in cetaceans. We cannot talk about morphological exceptions to Dollo’s rule without mentioning Atavism. Atavism by definition is a revision/reappearance to an ancestral characteristic previously lost in the evolutionary pathway (Biology-online, 2012). Atavisms arise normally due to a gene recombination or a gene mutation that enables a previous trait to be expressed (Hall, 2010). Hind leg extension in vertebrates has been well documented. In a study by Bejder Hall, they mention atavisms and the development of limb bud in cetaceans, snakes and legless lizards (Bejder Hall, 2002). They aren’t as rare as one might think this is due to all these animal species having being evolved from limbed ancestors, and as previously mentioned that genes can code for a multiple of different functions. Atav isms in whales normally occur in the rudiments of the pelvic girdle, the best case of this has been found in sperm and blue whales. The incident rate of atavisms in adult sperm whales is about 1:5000 (Bejder Hall, 2002). In the Individuals found the atavisms skeletal processes are found to be almost complete, even both hind limb have been found in a female humpback whale when normally present is cartilaginous femur (Bejder Hall, 2002). Because these vestigial limbs actually have no function can these actually be considered against Dollo’s law? Or because that previously forgotten traits are being expressed does that counter Dollo’s law? Another morphological feature that contracts Dollo’s is re-evolution of shell coiling in gastropods (Collin Cipriani, 2003). The trait was thought to have died out around 10mya but a study has shown that It can be re-evolved using the same genes that gastropods has at that time. There are two hypothesis put forward by this ide a; either that genes that signal for shell coiling have a number of function have been kept in there entirety, or that Trochita has developed a new pathway to gain the coiling trait completely different to its ancestor (Collin Cipriani, 2003). There has been evidence to support the second theory due to the coiling being superficially different to other gastropod species (Collin Cipriani, 2003). Finally an example that is a little closer to home is that there is new evidence of muscle reversions in the primate phylogeny. There have been 220 character state changes that are optimised in the parsimonious 28 of there have been evolutionary reversions, 6 of these have through evolution have contributed to human musculature and 9 of these have directly gone against Dollo’s law (Diogo Wood, 2012). The one particular case of violating of Dollo’s law for muscle reversion is in the subtribe hominina. In this case both the rhomboideus major and rhomboideus minor muscle are fou nd in an ancestral clade. This was then lost and the Rhomboidus muscles became the more distinct muscle in the Cercopithecinae, the ancestral muscle formation then has re-appeared in the Hominina there by going against Dollo’s law (Diogo Wood, 2012). this constant muscle evolution and re evolution causing the muscle to constantly re configure in primate to truly go against Dollo’s law at both eh morphological and genetic level there must be the same genetic pathways and selection pressures present to make this change a selective and adaptive advantage to truly call this change re-evolution. In summary to this review all of the studies all show great strengths and flaws with the methods and rules abided by in Dollo’s law. Constraints and contingency way heavily on if Dollo’s law is applied, because pathways may be constrained but if they actually help the re evolution of a trait there still may not be a selection pressure for these and this does not apply with the constraints of evolution, there-fore if there is no selection to me it feels like a random mutation with no beneficial attributes to the animal’s evolution. Law I feel is a strong word to use because with law there needs to be the same degree of lenience with this. This is due to papers on the genetic level saying that if the same pathways are used this means that this is against Dollo’s law, but if the same trait appears again but using a different pathway this does not, even if the new trait is a functional advantage. I believe the only way that a species can truly re-evolve traits is that the trait that has been re-evolved needs to be on a functional basis. The functional basis is that under Dollo’s law even if a limb has arisen That limb would need to be functional i.e. have a selection pressure causing this to be an advantage evolutionally. This is the only way that I can see of being able to out rightly say if something is against Dollo’s law. Word count: 1565 References : Bejder, L. Hall, B., 2002. Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss. Evolution Development, 4(6), pp. 445-458. Biology-Online 2014. Atavism definition from Biology-Online.org. [ONLINE] Available at: http://www.biology-online.org/dictionary/Atavism. [Accessed 27 February 2014]. Bull, J. Charnov, E., 1985. On Irreversible Evolution. Evolution, 39(5), pp. 1149-1155. Chopra, S. Rogers, K., 2013. Dollos law (biology) Encyclopedpia Britanica. [Online] Available at: http://www.britannica.com/EBchecked/topic/168293/Dollos-law [Accessed 24 febuary 2014]. Collin, R. Cipriani, R., 2003. Dollos Law and the re-evolution of shell coiling. Proceeding of the royal society of biological sciences, pp. 2551-2555. Diogo, R. Wood, B., 2012. Violation of Dollos Law: Evidence of muscle reversions in primate phylogeny and their implications for understanding iof ther intigeny evolution, and anatomical variations of modern humans. Evolution, 66(10), pp. 3267-3276. Hall, B., 2010. Atavisms. [Online] Available at: yadda.icm.edu.pl/yadda/element/bwmeta1.elementaab2/main.pdf [Accessed 27 02 2014]. Marshall, C., Raff, E. Raff, R., 1994. Dollos law and the death and resurrection of genes. Proceeding Of The Natural Academy Of Sciences Of The United States Of America, Volume 91, pp. 12283-12287. Seher, T. et al., 2012. Genetic Basis of a Violation of Dollo’s Law: Re-Evolution of Rotating Sex Combs. Genetics, 192(2), pp. 1465-1475. Yedid, G., C. A. Ofria, and R. E. Lenski., 2008. â€Å"Historical and Contingent Factors Affect Re-Evolution of a Complex Feature Lost during Mass Extinction in Communities of Digital Organisms.† Journal of Evolutionary Biology 21, no 5. pp 1335-1357.

Kung Bushman Essay -- essays research papers

The !Kung Bushman Most contemporary foraging groups, such as the !Kung and other Bushman tribes, are viewed as a â€Å"primitive† people. Some have even gone as far to say that they are â€Å"the last representatives of the stone age.† While it is true that these people have the most similar culture to what we believe primitive persons to have had, the analogies they can provide us with the people of the past are very inaccurate. These comparisons are so unrivaled due to factors such as time and the wrong sense of view many people have on them. Another reason that we cannot compare the !Kung of today to the people of the past is because they are now advancing in society with the use of technology. I believe that the !Kung tribe is not comparable to the early people of their culture and that they are just the same as us minus our technology, which in no way makes them ‘primitive’ people. First of all, every culture varies in traditions over time. According to Shostak, it is t rue that the !Kung people still have traditions that have been passed down for hundreds of generations such as their poison arrows, their trance ritual, their wide knowledge of over five hundred species of plants and animals—knowing which are edible, harmful, cosmetic, and medical. Who are we to say that these traditions have not been altered in the past ten thousand years? Howell declares that the !Kung were a very studied group including their language, culture, and economic organization. Although they have been extensively studied, Howell also proclaims, â€Å"It is surely illegitimate to use them as though they are the prototypical hunter-gatherers, knowledge of whom tells us all we need to know in order to apply the ethnographic analogy to models of prehistoric life.† Wild, maniac, unsophisticated, uneducated, vulgar†¦these are all words that come to mind when I think of prehistoric or primitive. Obviously the !Kung tribe have grown with the rest of society. How are we to say what the differences of prehistoric life was to the modern day !Kung tribes? Human error would play a huge role in our â€Å"assumptions† of the !Kung. For example, we might turn around to be just as wrong as the article of the Nacirema. Obviously, there is already a misconception about the bushman. For example, in McNeil’s essay, he comments on how a woman was speaking to a bushman and demanded to see one. When he explained ... ...† The bushman are pretending to be people they are not, giving the tourists what they want. This also gives tourists the wrong impression and significantly aids in the ignorance of the !Kung. This would be devastating to their culture. Culture, after all, is associated with the changes a society goes through over time. If these ‘prisons’ were to be set up, the culture would be forced and therefore in no way a comparison to early persons. Obviously, the !Kung have a very unique culture compared to how we live our lives. They in no way, however, represent what the culture of early persons to have. They have their own culture, unique to their society, and like ours†¦ever changing. What most people consider â€Å"primitive† is an ethnocentric remark to the difference of their culture to ours. The !Kung just have their very own technology, which is very efficient seeing that they survived this long. Due to time, ignorance, and the bushman’s leanin g towards our methods, they in no way can be compared to early people by means of their culture. The !Kung Bushmen are living their own lives now, in the present, therefore they can be in no way considered ‘people of the past.’ Word Count: 1024

Sailing Me

What do I really feel? Well, right now, I could say that I am sane. It just sounds funny to say that last word. For some time now, I have been holding a huge rock with my bare hands. The rock symbolizes my life as an adult human being. As an adult of early twenty’s of age, I began to struggle with life. I had worked for two independent companies already in a span of three years. But still, I have not yet found the contentment I am looking for. I mean, may be you would say that people usually have no contentment. But for me, I will continue to strive to gain recognition from my works and deeds so that it will feel rewarding and become a simple form of my contentment. That is why I am always making use of my abilities, skills, and knowledge the best way I can to show how flexible and competitive I can be in every job opportunity that comes my way. I think that is the smartest way to achieve one’s goal. Love life? I had two colorful love affairs already. I would like to share about the second. I and Gervin were actually friends. We were classmates in elementary. We lived in the same town until high school. I excelled during our elementary years, while he excelled academically in high school. After high school, we were not able to see each other except when there is a reunion held for our batch. Until one day, this year, when I forwarded messages to all the contact numbers of my friends I have in my phonebook, he was the only one who replied and asked how I am doing. It started like that. Everyday I receive messages from him. We converse through text messages, until it came to a point where he became romantic in his messages. Honestly, I liked how it feels. It was flattering. It made me fall for him after some time. For me, it was a cute, simple romance where we expressed our feelings to each other by sending text messages everyday. He was sweet to me. I was sweet to him, too. There were exchanges of I love yous and we understand each other. Although we were not actually seeing each other, I could feel his presence through his messages. And I felt like we were true lovers. The relationship became complicated when I learned that he has a girlfriend. I felt bad about it. Without further thinking, I messaged him immediately and said that I want to stop whatever it is that is happening between us. He did not make a reply. Until now there is no communication between the two of us. I wonder how he really felt about me and how he feels about me right now. What was his real intention to me? Was it just friendship, more than friendship, or just a flirting? If it’s just friendship, he actually hurt me because he is special to me. It was not clear to me what our relationship was. Finally, I am able to accept that I am human and it is normal to feel something special for somebody. It is better to let go of the feeling than to hide it. After heartaches and pains, it’s now time to enjoy life. I want to change my lifestyle, my career path, and everything about me. It’s time to be happy and to share my smiles to everyone especially to my family who most deserves it. But of course I need to earn money and to work hard for my living also. Life’s like that. Go for gold!

Pros and Cons of Using Ethanol Biofuel E85

Approximately 49 million ethanol flexible-fuel cars, motorcycles and light trucks were sold in the United States by mid-2015, yet many buyers still remain unaware that the car they own can utilize E85. E85 is 85 percent ethanol and 15 percent gasoline.   Ethanol is a biofuel that produced in the U.S. with corn. Ethanol fuel  is  ethyl alcohol, the same type of  alcohol  found in  alcoholic beverages.  It has been part of the nation’s fuel supply for almost 40  years. Research shows that ethanol may help lower fuel costs, improve air quality and increase octane. Ethanol can be used in any vehicle and is covered under warranty by every automaker in the U.S. Some cars can use more ethanol than others. What Is a Flexible-Fuel Vehicle A  flexible-fuel vehicle is  also known as an  alternative fuel vehicle  with an  internal combustion engine designed to run on more than one  fuel, usually, gasoline  blended with either  ethanol  or  methanol fuel, and both fuels are stored in the same common tank.   Vehicles That Are E85 Compatible The U.S. Department of Energy tracks fuel economy information and helps consumers perform flex-fuel cost comparisons and calculations. The department also maintains a database of all E85 compatible vehicles.   Flexible-fuel vehicles have been produced since the 1990s, and more than 100 models are currently available. Since these cars look just like gasoline-only models, you may be driving a flexible-fuel vehicle and not even know it. Advantages of Flex-Fuel Vehicles Switching to an ethanol-based fuel moves us further from using up our depletable fossil fuels and closer to U.S. energy independence. Ethanol production in the U.S. primarily comes from corn. In the American Midwest, corn fields are set aside for ethanol production, which has been shown to have a positive effect on job growth and stability. Ethanol is also greener than gasoline because corn and other plants absorb carbon dioxide from the atmosphere as they grow. The fuel still releases CO2 when you burn it, but it is believed that the net increase is lower. Any car since 1980 has been designed to handle up to 10 percent ethanol in the gasoline, letting you run that percentage of your miles on a domestic fuel rather than irreplaceable fossil fuels. Disadvantages of Flex-Fuel Vehicles Flex-fuel vehicles may not experience a loss in performance when operating on E85, in fact, some generate more torque and horsepower than when operating on gasoline, but since E85 has less energy per volume than gasoline, flex-fuel vehicles can get up to 30 percent fewer miles per gallon when fueled with E85. This means you will get fewer miles per dollar spent. If filling up with flex-fuel is what you want, then finding a flex-fuel station might be a little difficult. Only about 3,000 stations across the U.S. sell E85 at the moment and most of those stations are in the Midwest. To give you some perspective, there are about 150,000 gas stations in the country. Despite the promising research, there are still question marks regarding the agricultural impacts and real energy balance of growing crops to use as fuel.