Evolution Notes Week 1
Evolution Notes Week 1 Anth 314
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This 3 page Class Notes was uploaded by jewellog on Friday October 9, 2015. The Class Notes belongs to Anth 314 at James Madison University taught by Dr. Harlacker in Fall 2015. Since its upload, it has received 10 views. For similar materials see Human Evolution in anthropology, evolution, sphr at James Madison University.
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Date Created: 10/09/15
090315 Thursday September 3 2 15 1355 Basics of Evolution Genetic Drift random shift in geneallele frequencies caused by randomness in the reproductive process 0 Some individual may not get the opportunity to reproduce despite being fit for their environment like a natural disaster 0 This can also happen due to which alleles actually get passed on during reproduction This is especially important to small populations because smaller populations are more greatly affected by any one random change Founder Effect when a small subset of a population becomes separated or isolated from the larger population due to some random change they can then go on their own evolutionary journey Genetic Bottleneck the breeding population for a species becomes really small for a short time you may lose a lot of genetic variation and only have a smaller subset of variation Gene Flow Movement of alleles from one population to another 0 You will always have some degree of gene flow between populations 0 This increases the variation within population and decreases variation between populations This can happen when you have population migration or even with pollination Mixture of genes from one population to the next Mutation adds new genes and recombination adds new combinations and gene flow add new variation to a given population monkey chart It is only a case when there is a correlation between a trait and fitness that you can see a change in evolution in that trait If there is a correlation then you will see selection and across generations there will be movement towards whichever end of the trait is favored tail length 0 This could be called an adaptation 0 We would need to test that those with longer tails are actually reproducing more Adaptationism It makes sense to want to come up with adaptive explanations for almost all traits in any organism Many traits are regarded as optimally shaped by natural selection Natural selection is regarded as very powerful and is the major contributor to animal form Not all traits are adaptive but they would be explained under this umbrella as the result of trade offs 0 An organism would be viewed as an optimal compromise to solving the survival problem This came under critique in the 7039s there is debate over whether or not this was mostly straw man 0 Gould and Lewtonin 1979 attacked the adaptationism paradigm and they wanted to start considering other reason that would influence the traits we see and their distribution 0 We don39t want to assume wo evidence that we are looking at truly optimal fits to the environment 0 quotNot really survival of the fittest but survival of the fit enoughquot Not optimality but being better than others Not everything is necessarily an adaptation at all Spandrels In San Marcos Cathedral which are triangular spaces which are the inevitable result of mounting a dome on a set of arches and are usually filled in with decoration they are used In evolution a spandrel is something that looks like it has an adaptive purpose but may not in actuality BELLY BUTTONS Kinds of Selection Stabilizing Selection when the two extreme ends of a trait aren39t selected for and so the Human Evolution Page 1 population collects near the mean of the trait O This can get rid of new extreme variations in the population this tends to maintain good traits in a population 0 Fourchambered heart birth weight Directional Selection when one end of the trait isn39t selected for and the population moves towards one extreme of the trait Disruptive Selection when the mean of the trait isn39t selected for and the population moves towards each end of the trait o Moths being either white or black would be safe in rural or urban environments respectively but grey moths would do poorly in both environments Adaptation Some traits are adaptations some are neutral and some are detrimental to survival but why This could be due to balancing selection Balancing Selection a force that works to maintain polymorphisms Polymorphisms stable frequencies of multiple phenotypes So anyone with one copy of a sicklecell anemia allele can be immune to malaria whereas someone with none is not and someone with both is already at risk due to having sickle cell anemia this depresses fitness This could keep a potentially harmful allele more frequent Heterozygote advantage an adaptive advantage for those who have only one copy of an allele above those who have no copies or two copies Sexual Selection Selection driven by competition for mates acts on animal39s ability to obtain a mate Darwin viewed this as very different from natural selection and had a second book for it Selection in Relation to Sex This is only important in sexually reproducing creatures This is generally more important to males due to malemale competition to try to have access to females in a population Males will be jockeying for position in the hierarchy those at the top have more mating success Or you have a population with only one male who gets his choice of females Female choice is also important 0 Males may not be directly competing with each other but may be attempting to appear more attractive and thus healthier O Handicap Principle males who put resources that are good for mating but bad for everything else IKin Selection How do individuals choose who they will be helpful for or altruistic towards Sharing food with siblings because they will be able to pass along the gene line Initially hard to explain based on individual natural selection because they would be losing resources for themselves Inclusive fitness notjust looking at one39s own reproductive success but also looking at the reproductive success of relatives as well The closer related you are the bigger a sacrifice you may be willing to make Marmosets can be either monogamous or polyamorous 0 Many will help the nest before the go out and find a mate even after they have reached sexual maturity especially in times of resource scarcity You can increase the chances of having that altruism being given back at you in the future This indicates high levels of intelligence in terms of selfawareness theory of mind and future planning Limitations to Evolution Rates are limited by things like birth interval how quickly a species reproduces o This is why we struggle with antibiotics because these change so quickly 0 Humans are on the opposite ends of things because we are unable to respond quickly to Human Evolution Page 2 new environments Types of change are limited because evolution can39t go back to the drawing board it will be constrained by the variation that currently exists or is possible in a given population 0 Fitness landscapes there is more than one way to have high fitness in a given environment you may not be able to jump from one to another because to do so would involve a decrease in fitness like jumping from one hump to another in a bimodal curve 0 Path dependence the whole evolution of one feature in order to see the possibilities for that feature Four C39s Conditions context in which the event occurs environment habitat climate weather patterns Causes selective pressures whatever it is that may change a trait Constraints starting conditions plus physical or physiological constraints these will limit the responses a species may have Consequences the evolutionary change the shifting of the value of a trait and creating a change in the species Examine each of these to explain various evolutionary changes and their origins Human Evolution Page 3
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