Bio 1B Spring 2008 Evolution section 1 of 3 Lecture 1 Updated 2 28 08 10 11 AM 1 Darwin and The Origin of Species Reading 7th edition 438 446 6th edition 428 437 The Origin of Species is not required reading but copies of the first and sixth editions are freely available from the Gutenberg Project www gutenberg org Logistics Office hours Monday Tuesday Wednesday 9 10 2013 VLSB or by appointment slatkin berkeley edu Responsible for material in the lectures and lecture notes If material is in the text but is not covered in the lectures and notes it will not be on the exams Updated versions of the notes will reflect what is presented in lectures Examples from the labs and the lectures will be on the exams Sample exam questions will be included with each set of notes They are intended to show the types of questions asked on the midterm and final but not the whole range of topics that will be covered The 2nd midterm 6 PM on Friday April 11 will be on all the material in the evolution section including material presented on Wednesday April 9 Any theory of evolution must have three parts The fact of evolution All living organisms are descended from other living organisms and ultimately from one or a few ancestors Darwin called this idea descent with modification The pattern of evolution The pattern is what actually happened Darwin said that the pattern was gradual and continuous not discontinuous The mechanism of evolution Darwin argued that natural selection alone caused descent with modification Uniformitarian assumption Darwin s theory is based on what is now called the uniformitarian assumption or the assumption of natural law The uniformitarian assumption is that the rules governing change were the same in the past as they are today The name uniformitarian comes from the uniformitarian theory of geology which argued that changes in the earth s surface are the result of processes at work today For example sedimentary rocks were the result of erosion Darwin was strongly influenced by the book Principles of Geology by Charles Lyell which he read during the voyage of the Beagle Lyell s book convincingly advocated the uniformitarian theory of geology The alternative to the uniformitarian assumption is that changes in the past occurred because of processes that are no longer acting and hence cannot be observed today in other words supernatural processes The uniformitarian assumption does not mean that all change has to be slow and gradual A volcanic eruption a major earthquake and the impact of a large Bio 1B Spring 2008 Evolution section 2 of 3 Lecture 1 Updated 2 28 08 10 11 AM meteorite can produce nearly instantaneous changes but they do so in accordance with laws of physics and chemistry The uniformitarian assumption does not mean that rules governing changes in the past are completely understood or that events are completely predictable Weather is governed by the rules of physics and chemistry Yet meteorologists cannot perfectly predict the weather even one day in advance The uniformitarian assumption is the basis for all historical science including astronomy geology and archeology The acceptance of the idea that all past events were governed by laws that can be studied today led an intellectual revolution Past events could not only be described but also explained The reason for emphasizing the uniformitarian assumption in the study of evolution is that it is at the root of most objections to evolution Outline of the Origin of Species 1859 Domesticated species The first chapter presents evidence that there is extensive variation within domesticated plant and animal species Then it presents evidence that differences among individuals are inherited and that choosing as parents individuals with desired characteristics results in steady improvements of existing breeds and varieties and in the creation of new breeds and varieties This process is called selective breeding or artificial selection Darwin used horses dogs and pigeons as examples He said that there appeared to be no limit to what can be achieved by selective breeding The facts presented were generally known and were not controversial Variation in natural species The second chapter reviews what was known about variation in natural species Darwin emphasizes that there is variation within all natural species and that variation is of the same type and extent as is seen in domesticated species Darwin used many species of British plants as examples These facts were also known and not controversial Struggle for existence The third chapter introduces Darwin s essentially new view that natural species are continually in competition for space food water and other resources The struggle for existence is against other members of the same species against members of other species and against the physical environment All animals and plants have many more offspring than can possibly survive making the struggle for existence inevitable The view of nature that Darwin presented was very different from the widely accepted view of the natural theology which emphasized the harmony of nature and the perfection of creation The ideas in this chapter were influenced by an essay on human populations written Thomas Malthus first published in 1798 Malthus argued that human populations inevitably increased more rapidly than their food supply Natural selection The fourth chapter describes Darwin s mechanism of evolution natural selection as a necessary consequence of what he presented in the second and third chapters Differences among individuals in their abilities to succeed in the Bio 1B Spring 2008 Evolution section 3 of 3 Lecture 1 Updated 2 28 08 10 11 AM struggle for existence result in some individuals having more offspring than others Offspring that inherit the traits that made their parents successful in the struggle for existence will themselves be more successful As a result the composition of the species changes slightly from one generation to the next as the more successful types became more frequent Darwin said that as with selective breeding there was no limit to changes that could result from natural selection It is the species that evolves because of changes in composition from generation to generation Individuals do not evolve Darwin emphasized that no characteristic could be present only because it benefits another species He used nectar in flowers as an example Sample questions a b c d e a b c d e a b c d e a b c d e Which one of
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