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Why Evolution Is True. chp 1 and 5.doc

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University of Toronto St. George
June Larkin

03/06/2012 22:45:00 Why Evolution Is True? Chapter 1 So what is Darwinism? • The theory of evolution by natural selection • Life on earth evolved gradually beginning with one primitive species- perhaps a self replicating molecule that live more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species and the mechanism for most of evolutionary change it natural selection Consist of 6 components: evolution, gradualism, speciation, common ancestry, natural selection and nonselective mechanisms of evolutionary change 1. evolution: that species undergoes genetic change over time, that is, over many generations a species can evolve into something quite different and those differences are based on changes in the DNA, which originates as mutations 2. Gradualism: it takes many generations to produce a substantial evolutionary change such as the evolution of birds from reptiles. Gradualism doesn’t mean , however that each species evolves at an even pace, when natural selection is strong as when an animal or plant colonizes a new environment evolutionary change can be fast. 3. Speciation(splitting): Single ancestral species that split into two descendent species, one splits more and causing more species and the other split causing other different speciescommon ancestor is called the missing link btwn two different descendant groups …what happens if ancestor x split into two separate species? Nothing much • Speciation means the evolution of different groups that cant  interbreed that is groups that cant exchange genes ( why split members of different animal species may no longer find each other attractive or if they do mate with each other the offspring couple be sterile. • All the important change happed thousands of generations after the split when selection acted on one linage to promote the flight and on the other to promote the traits of bipedal dinosaurs • Speciation doesn’t happen very often but each time one species splits into two, it doubles the number of opportunities for future speciation so the number of species can rise exponentially 3. Common Ancestry: it simply means that we can always look back in time using either DNA sequences or fossils and find descendants joining at their ancestors • Backbone  vertebrates  all united by having amniotic egg-the embryo is surrounded by fluid filled membrane called amnion • Hierarchy: a hierarchy in which big groups of species whose members share a few traits are subdivided into smaller groups of species sharing more traits and so on down to species like black bears and grizzly bears that share nearly all their traits • The natural classification is itself strong evidence for evolution • By sequencing the DNA of various species and measuring how similar these sequences are we can reconstruct their evolutionary relationships. • The idea of common ancestry leads naturally to powerful and testable predictions about evolution 5. Natural Selection: if individuals within a species differ genetically from one another and some of those differences affect an individual ability to survive and reproduce in its environment, then in the next generation the good genes that lead to higher survival and reproduction will have relatively more copies than the not so good genes • the population will gradually become more suited to its environment as helpful mutations arise and spread through the population while deleterious ones are weeded out. • This process produces organisms that are well adapted to their habitats and way life • Natural selection and evolution are inevitable • Natural selection must also work with the design of an organism as a whole • Mutations are changes in traits that already exist; they almost never create brand new features, this means that evolution must build a new species starting with the design of its ancestors • Natural selection only improves what came before . it produces the fitter not the fittest 6. nonselective mechanisms of evolutionary: the most important is simple random changes in the portion of genes caused by the fact that different families have different numbers of offspring. This leads to evolutionary changes that , being random, has nothing to do with adaption Science, a theory is much more than just a speclection about how things are : it is a well though out group of propositions meant to explain facts about the real world The theory of evolution is more that just the statement that evolution happened evolution happened: it is an extensively documented set of principles ( 6 compents ) For a theory to be considered scientific it must be testable and variable predictins. Darwinism can also be supported by what I call reproductions: facts and data that aren’t necessarily predicted by the theory of evolution but make sense only in light of theory of evolution. Chapter 5 Natural Selection poses number of problems for biology. 3 things are involved in creating an adaption by natural selections 1. the starting population has to be variable: mice within population have to show some difference in their coat colors. Other wise this trait can not evolve. In the case of mice we know this true because mice within mainland populations show some variability in coat color 2. some proportion of the variation has to come from changes in the form of genes that is the variation has to have some genetic basis Where do genetic variation come from> Mutations- accidental changes in the sequence of DNA that usually occur as error when the molecule is copied during cell division Mutations occur regardless of whether they would be useful to the individual, Mutations are simply errors in DNA replications. 3. genetic variation must affect an individuals probability of leaving offspring. • Evolution by selection then is combination of randomness and lawfulness. There is first a random process – the occurrence of mutations that generate an array of genetic variants, both good and bad and then a
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