Tuesday, April 14, 2009
Rate of Evolution
On pages 64-65, Caroll explains how what may seem like an eternity to a human, "is barely a tick of the evolutionary clock." Throughout the book, Caroll consistently relates evolution back to three main components - variation, selection, and time. Is the amount time necessary to develop advantageous traits consistent throughout evolutionary history? What type of factors within an organism's ecosystem contribute to the rate of evolution? How can scientists determine this? (Possibly connect to neutral mutations). Humans have arguably become the dominant species on Earth. How has this affected these mutational rates in the human species and in other organisms that we have inevitably affected?
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Some of the feats of evolution are amazing and the time that it takes to develop these diverse and innovational selective advantages most likely require seemingly an eternity. But considering the question of the development of advantageous traits is consistent throughout evolutionary history, one must consider the fact that the development of certain traits take longer than others.
ReplyDeleteFor example on page 106 Carroll mentions that trichromatic vision developed in primates with the duplication of an opsin gene and natural selection fine tuning the new opsin gene to a different range of color. A small number of mutations separate the different number of opsin genes from being identical. On page 105 the diagram shows the green and red shift in pigment detection is separated with mutations on only three different sights. The process of remodeling the genetic code for selective advantages and other evolutionary development is relatively quick compared to the development of complex structures that was not similar in any aspect to the preexisting genes at that time. The remodeling process is just one mechanism of natural selection that requires a certain amount of time different than other mechanisms.
This can be compared to the rapid development of melanic moths over the original masses of the lighter colored pepper moths in England. The classic example of natural selection follows as such, with the pollution of the emerging industrial evolution, the soot and darkening of tree lichen caused the advantageous selection of melanic moths. While originally rare, in this new development, there is an extremely rapid rise of frequency of melanic moths. This classic model has been coined as microevolution as the variation from a specific mutation existed in the population of peppered moths, and with changing environmental conditions, the variation of darker moths were selectively chosen over the lighter moths. This microevolution and the development of an advantageous trait could happen more rapidly than the remodeling process of opsin genes for trichromatic vision in primates. It requires a different amount of time to transpire.
What the question is most likely referring to is the development of an advantageous trait that is not already existing in the variations immediately available to a specific population of organisms. There are no genes that are already extremely similar to the supposed function of the advantageous trait, and these kinds of evolutionary development can take seemingly an eternity to develop. For example the development of hinged jaws in bony fish came from a modification of the pharyngeal slits and the bone surrounding the structure. This much is obvious in the change of suspension feeding to a more useful mechanical digestion and a larger diversity of food options. This is also a more extreme example of the remodeling process found in natural selection that has taken the eternity the question refers to. But under these conditions and numerous examples, evolutionary development occurs with different time restraints considering the variability immediately available in the species and the similarity between an evolved trait and another preexisting gene. When put in these classifications, natural selection does remain consistent throughout evolutionary history.
Environment has a major effect on evolution and probably is one of the major selective forces that drive evolution. Under the idea of “Survival of the Fittest,” the best adapted variations are chosen to survive under the environmental conditions and allowed to pass on to the successive generations, While the least able to survive are eliminated from the gene pool and is not allowed to pass on to successive generations. This idea is rudimentary. Some environmental factors that lead to evolution is predation, changing climate, presence of water, exposure to light, temperature, competition, immediate surroundings, etc. The list is endless, and it stands as the number one cause of the great diversity of mutations in the gene pool of an infinite number of diverse organisms. Environmental factors affect the evolutionary rate by increasing the variability of genes and leading the which selective alternative is best suited for the changing environment. As for the notion of neutral genes, the advantages of both cancel the dominance of one’s existence in a population, so there becomes more variability with the neutral theory.
Regarding the last question, it is hard to compare the evolution of humans and organisms as there is a great number of different aspects that factor in the analysis of human evolution. Humans are under extremely different environmental conditions than the norm for many other organisms in nature and under the full selectiveness of survival in these settings. In the humans, natural selection seems more relaxed, which can alter the perspectives of human evolutionary processes. But in the case of environmental conditions, the wide range of effects that humans have has become another factor in the set of environmental conditions other organisms face. Like the example of the melanic moths and how their rapid rise in frequency was greatly due to the massive increase of population in the surrounding area. The inhabitance of humans has become another effect in the evolutionary process of other species.
http://en.wikipedia.org/wiki/Evolution
ReplyDeletehttp://www.actionbioscience.org/evolution/eldredge.html
http://www.biologie.uni-hamburg.de/b-online/e36/36.htm
Make of the Fittest
Evolution takes place under several changing environmental conditions, which forces organisms to continually readapt. However, a study done at the Institute of Molecular Cell Biology and Physics of Complex Systems department has created a computer simulation that mimic natural evolution. Their studies showed that the more generations needed to achieve a “selected mutation”, under fixed conditions, the faster evolution accelerated in response to changes in that goal.
ReplyDeleteOne of the fastest rates of vertebrate evolution ever recorded was done by Tom Johnson from the University of Minnesota, Duluth. An array of brightly colored fish, known as Cichlids, live in east Africa’s Lake Victoria. These cichlids have evolved from a few ancestors, and the first burst of speciation began only 100,000 years ago. These cichlids have evolved into insect eaters, leaf choppers, snail crushers, and scale scrapers which are all seemingly similar traits, that are linked to very different genetic differences.
According to the study, cichlids from Lake Kivu colonized Lake Victoria, which set the stage for the rapid evolution of over 500 cichlid species. No waterways connect the two lakes now, however the scientists suspected that ancient rivers had. A study of the two environments showed that Lake Victoria had a highly reflective layer lying at the bottom of the lake, causing an increased refraction of sunlight within the water. That, along with the fact that Lake Victoria was located on a marsh, changed the environment from a deep, dark habitat (Kivu), to a shallow, bright habitat. Therefore, the cichlids were forced to change rapidly in order to avoid death.
http://www.sciencedaily.com/releases/2007/08/070828084425.htm
https://www.geology.ucdavis.edu/~cowen/historyoflife/evolutionlinks.html
http://www.geotimes.org/apr03/WebExtra042503.html
As Sean Carroll says time is an important factor promoting the evolution rate. There are many factors that contribute to an organism’s evolutionary rate, random mutations by Chance, and natural selections such as predators and limited space or food. We already know how important natural selection is in evolution. Sean Carroll talks about natural selection every single page in the book. Therefore, I will more focus on the mutation rates and how it is closely related to the evolution rate.
ReplyDeleteMutation happens randomly and in every organism in the world. Because of mutation, we are allowed to evolve. Therefore, scientists figured out that if we are able to measure the mutation rate, we will be able to guesstimate how often evolution occurs in given time. According to Patricia Foster, mutation is like a slot machine. Mutation happens every day but it is extremely rare to get a jack pot. According to her study, this involved culturing e.coli bacteria with newly introduced gene and recording the mutation rate. As a result, the bacteria with mutation grew in population linearly which means that mutation rate was time dependent rather than replication dependent. This shows that time is one of the most important factor in evolution because it seems like mutation rate is time dependent. More time an organism is exposed to environment, it is more likely for them to have mutation and then natural selection can sort good mutations from bad mutations.
Humans are maybe the most interesting creature on the earth. I think that humans have become immune to natural selection and no matter how much time is passed; they will stay the same because they have all the protection they need from natural selection. We can always make new houses to protect us from harsh weather, guns to protect from predators, and drugs to fight bacteria. This shows that evolution does not depend on only one component. It is the combination of variation, time, and selection that drives the process of evolution.
http://www.pnas.org/content/96/14/7617.full.pdf+html
On page 64-65, as Carroll is discussing the fact that what seems like an eternity is really only a small tick on the evolutionary clock, he mentions that “our ancestors’ brains doubled in size in 1 million years”. This is interesting because we keep thinking that we aren’t evolving, but we can clearly see a difference in brain size. We as humans live only up to about 100 years or so, at best. There is no way for a person, in one lifetime, to see evolution actually happen. Plus, people do not evolve over their lifetime, it is a process that happens over hundreds of generations.
ReplyDeleteAccording to a science website, the time of evolution has remained relatively consisted throughout the years. Although there have been some eras that last longer than others, based on a consistency level, it has remained relatively stable. It is interesting to note that the mammalian era, ““The Cenozoic Era”, marked the end of the dinosaurs and the emergence of mammals and birds. Although primitive mammals and birds first appeared in the Mesozoic era, it was not until the Cenozoic Era that they really emerged as powers in the world.” This era has only been around for a very short period of time; as of right now, mammals have been present on earth the shortest amount of time out of all species that have lived here. Even so, we have become the dominant species and take the Earth to be our own and do things only for us.
To connect this to a biological theme, evolution would be the theme discussed here. Scientists have recently been disputing the question of whether or not humans continue to evolve. The fact that humans have become the dominant species on earth may or may not affect evolutionary mutations. For humans, I believe that it is drastically affecting evolutionary mutations because humans are possibly having mutations that are disadvantageous, but the fact that we have so much medicine and etc, it doesn’t really matter. Essentially, we are cheating nature. We need to understand that what we are doing to prevent death, medically, is preventing or possibly cheating evolution. I do believe, though, that humans still continue to evolve. There are some mutations that medicine cannot affect.
One evolutionary change is the fact that our olfactory sensory genes are not as prevalent as they once were. According to an ABC article, “Humans rapidly lost much of their sense of smell as they evolved to place a heavier emphasis on their sense of sight, according to a recent genetics study.” Likewise, to answer the question posed, “hat decline took place within an 'evolutionary moment' of just three to five million years, and it happened four times faster in the branch of the evolutionary tree leading to humans than it did for other primates.” This is interesting because common sense would tell us that evolution for humans is slowing. On the contrary, it has actually sped up. There are many more experiments that claim that humans’ evolution has actually been sped up by technology.
According to an interesting Journal Article, “What we shall call the Panglossian view maintains that this past record of success gives us good grounds for thinking that evolution (whether biological, memetic, or technological) will continue to lead in desirable directions. This Panglossian view, however, can be criticized on at least two grounds. First, because we have no reason to think that all this past progress was in any sense inevitable‒-much of it may, for aught we know, have been due to luck. And second, because even if the past progress were to some extent inevitable, there is no guarantee that the melioristic trend will continue into the indefinite future.” This means that this study demonstrated that humans are in fact continuing to evolve and even have their evolution sped up by technology. Likewise, these scientists make the case for evolution, saying that it is inevitable; it will happen no matter what we do. Evolution is defined as “A gradual process in which something changes into a different and usually more complex or better form.” Humans are changing in some way; it does not matter if we are changing into a form that relies more or technology or what have you, we are in fact changing and that is the dictionary definition of evolution.
Scientists in a journal article stated “Even if the rise of intelligent life from simple replicators were a robust and nearly inevitable process, this would not give us strong grounds for thinking that the good trend will continue. One possibility, of course, is that a catastrophic event may cause the sudden extinction of the human species. Some existential risks arise from nature, e.g. impact hazards (meteors and asteroids), pandemics, astrophysical disasters, and supervolcano eruptions. But the greatest existential risks are anthropogenic and arise, more specifically, from present or anticipated future technological developments.” Basically, they said that humans can become extinct, just like the dinosaurs, through some sort of catastrophic event that can lead to failure of the earth as we need it. Likewise, recently, humans have developed so much technology that it may be becoming a risk to our evolution and our continuing as a dominant race. The scientists make the case for further development of nuclear arms and dangerous things that come about from humans’ need and thirst for power. This journal article was very much based from a social standpoint rather than a completely biological standpoint. But, at the same time, the scientists base their predictions and their theories on hard evidence that they have studied deeply.
Another article discussed the fact that humans are different from any other species because we have the intellect to create this sort of technology. This is a double-edged sword because on one hand, intelligence is a key part of the developing and evolving of a species, but on the other hand, technology may possibly be leading to our downfall. Either we are evolving way too quickly because of technology or we have stopped evolving. There continues to be much dispute over which is the correct answer to whether or not humans have stopped or continue to evolve.
http://www.ecotao.com/holism/bp.htm
http://www.abc.net.au/science/articles/2003/04/03/823577.htm
http://www.nickbostrom.com/fut/evolution.html
http://www.thefreedictionary.com/evolution
http://www.cscs.umich.edu/~crshalizi/Medawar/technology-and-evolution/
Mutations occur at chance, so it takes a substantial amount of time for a large amount of mutations to occur and thereby producing an advantageous trait. In terms of consistency, throughout evolutionary history it is safe to say that the time needed to cause any advantageous trait is constant. In terms of a single gene, however, the time needed to cause and advantageous trait can change substantially depending on the environmental factors of the organism. Since organisms have many genes, each with fluctuating selective coefficients depending on environmental factors, the overall time it takes to produce any advantageous mutation will stay the same. I will now explain why the time needed for a single advantageous trait to form.
ReplyDeleteMutations in DNA occur at about the same frequency during DNA replication, about 1 in 10,000 base pairs. In the final product of replication, about 1 in 1 billion base pairs is mutated. This rate is constant, so the number of mutations and organism has in a single gene is constant. We can therefore conclude that the molecular requirements for an advantageous trait remains constant no matter what. For a mutation to be retained and transformed into an advantageous trait, certain environmental factors must be present, and these factors are subject to change. There are an incredible amount of factors that affect the role a gene has in the survival of an organism. The best answer to what types of factors contribute to the rate of evolution is any factor that affects the survival or reproduction of a species. If we are discussing a single gene, then the answer would be any environmental factor that has an effect on the role that a gene plays in survival. For example, in discussing an opsin gene, what factors will affect its rate of evolution? To answer this, we must determine what environmental factors will make the the type of opsin a determining factor for survival. The amount of light would be an environmental factor that affects the speed of evolution in the opsin. In a given type of light, some opsins will benefit species' survival more than other opsins, so the amount of light causes opsins to play a role in survival.
This example shows how environmental factors can affect the speed of evolution. If we consider again light as a factor, what would happen to the speed of opsin evolution if the amount of light in an ecosystem stayed relatively constant over time. Would one predict fast evolutions in the opsin genes? No. If light conditions are not changing, there is no pressure from selection acting on the genes. Surely a mutation might come along that could be a benefit, but chance are that the current opsin genes of a species are perfectly adequate since light has been constant. Therefore, this new mutation will have a low selective coefficient, if any, and it is clear that the amount of light was the main factor in determining what this selective coefficient was. To determine how environmental factors affect the rate of evolution, scientists can simply see how a manipulated gene affects the survival of a species in different conditions. It is very hard to do this with most genes because in many cases it is hard to either predict what a mutation will do, or it is hard to simulate what a gene will do. One case where it would work is skin/fur color. It would be possible for scientists to genetically alter the fur color of say rats, and monitor their survival rates in different levels of light. It should not be misunderstood that a long period of time is necessary for an experiment like this. The scientists here are emulating the mutation, so the rats aren't “waiting” for a mutation, scientists are simply testing the selective coefficient of a given mutation in different conditions.
It is very unclear whether humans are affecting their own speed of evolution. Some argue that yes, modern medicine has caused many negative traits to go unnoticed, but the evolution of the brain makes up for these negative traits because one evolved trait in humans is our brains. The effects humans have on the evolution of other animals is without a doubt present, but as to how they are affecting other organisms, it is inconclusive because we are affecting other ecosystems in such drastic ways. I do, believe, however, that we are speeding up evolution in other species, because generally evolution speeds up when stress is put on an organism, raising the selective coefficients of many genes. As we have seen with bacteria, the stress we put on bacteria with antibiotics has caused their evolution rates to skyrocket.