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2_2 Evolutionary Theory_Lecture Script.pdf

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Simon Fraser University
ARCH 131
Dennis Sandgathe

UNIT 2 EVOLUTION AND NATURAL SELECTION 22 Evolutionary Theory Slide 1 Title slide Slide 2 Today scientists and properly educated people recognize that evolution is not a theoryit is the end result of processes of change that have always been occurring among life on earth The fact that this change has occurred can be easily verified By simply observing in geologic strata the changes in fossils through time we can see that species disappear and are replaced by new species that hadnt previously existedthis is not theory Slide 3 However the means by which these changes occurNatural Selectionremains a theory This is the case with all scientific explanationfor example that matter is composed of atoms is a theory that plants produce energy through photosynthesis is a theory However the evidence in support of Natural Selection as an explanation for evolution is so overwhelming and the explanatory potential of it is so powerful that nobody who has been properly exposed to it seriously questions it without their motives being suspect It has withstood scientific testing for well over 100 years Evolution has come to be recognized as one of if not the most fundamental of biologic processes It explains the incredible diversity of life on earth it explains the changes in life forms that are apparent in the fossil record and Natural Selection explains every single component of every organism that has ever livedfrom the structure of the cell to the human capacity and drive to conceptualize and construct material things Since one of the dominant focuses of Biological Anthropology is the change that humans have gone through over the course of our biological history and the ways in which we have adapted to our environments a good understanding of how evolution works is a necessity As weve seen already the idea of evolution predates Darwin by many yearsit wasnt the concept of evolution that he developed but an underlying mechanism by which evolution could occur in nature We recognize this as Natural Selection and while we have refined our understanding of the details of the evolutionary process the same fundamental mechanisms that Darwin and Alfred Russell Wallace recognized remain true Slide 4 The process of Natural Selection works on several fundamental premises that are based on observable natural phenomena Premise Number 1More offspring are produced by a species than could be supported by naturally available food supplies This means not all offspring will survive to reach maturity and reproduce therefore there will always be competition between the members of a species for survival Slide 5 This fact was noted by Thomas Malthus in his 1798 An Essay on the Principles of Population Malthus recognized that if unchecked animal populations would increase exponentially while food supplies would tend to remain stable within normal climatic shiftsIn the case of the majority of the animal kingdom this potential exponential growth is held in check by the limit on food resources This has not been the case with humansSlide 6 Over the last 2000 years or more we have rapidly overcome many of al checks on population growth especially disease and the naturlimited food supplies and so our population has been free to grow at an exponential rate
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