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Lecture 20

Bio120 Lecture 20 Notes

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Spencer Barrett

Bio Final Lecture 20 Notes This lectures topic is SPECIATIONWhat drives this diversificationThere is NO universal definition of a species there are different ones depending on usage For this course well use Darwins I look at the term species as one arbitrarily given for the sake of individuals closely resembling each other Darwin 1859ONE OF THE MOST IMPORTANT EVOLUTIONARY BOOKS GET IT 1Hawaiian honeycreepers have all evolved froma single species in only 10 million years But How When we understand the origin of reproductiveisolation we understand the origin of species Darwin didnt actually focus on speciation or evenactually understand speciation at all Key questions about speciation1 What ecological and genetic conditions are required for speciation to occur2 How does reproductive isolation evolve3 How many genes are involved and can we identify and isolate them Genes that once they become fixed with alternate alleles cause a reduction in gene flow between populations4 And is the adaptation always required for speciation The two major concepts over what a species isThe taxonomic concept which is often called the morphological species concept because its based on morphological species between conceptsBut the problem is that its somewhat arbitrary The question becomes how big has that gap got to be between populations to become distinct species For example human races So genetics came in to give a more objective definition which can also have problems The other concept is the biological concept However when you cant crossbreed individuals to test this concept for example with asexual or hardtoreach organisms like deepsea organisms this is not a great concept However we will be using this one Ernst Mayr Harvard defined the biological species concepta group of interbreeding natural populations that are reproductively isolated from other such groupsMayr 1942Dobzhansky first suggested the idea but Mayr first formally defined BSC On page 178 in Coyne Why Evolution is True it explains the theory of geographic speciationIts necessary geographic isolation is necessary for speciation to occur because the opportunity to crossbreed would be too great and heterozygosity would more likely occur than speciation well the last half
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