Continued The presence of AZT selects the HIV strains within an individual that possess RT variants that can preferentially incorporate thymidine rather than AZT allowing for growth into a viral DNA strand Therefore the non AZT incorporating HIV strains come to pre dominate individuals that have long term AZT therapy and the effectiveness of continued AZT therapy declines This is a medically relevant example of adaptation by means of natural selection o Example Round Up resistant weeds pesticides and bugs etc IV A Classification of the Field of Evolutionary Biology 1 The history of evolution pattern of organismic relationships a What are the evolutionary relationships among all forms on Earth b What was the order of character traditions that occurred during the evolution of life i Example one digit mammals v human five digit hands ii This suggests an evolutionary transition that occurred in the past 1 digit 5 digit or 5 digit 1 digit iii Which transition actually took place Reference to an estimate of the evolutionary history phylogeny of Mammalia can provide an answer 2 The Causes processes of Evolution a Major Causes i Natural Selection ii Mutation iii Recombination iv Genetic Drift v Isolation vi Gene flow b When did this list originate evolution c Some notable names i Evolutionary Synthesis 1930 1950s a combining of Mendelian genetics and Darwinian natural selection interaction of the two yields adaptive i Geneticists Ronald A Fisher J B S Haldane Sewall Wright Theodosius Dobinsky ii Paleontologists George G Simpson iii Systematicists Ernst Mayr zoologist G Ledyard Stebbins botanist V Classification and Phylogeny Evolutionary Patterns Classification a process of establishing diagnosing and ranking taxa within a hierarchical series of groups Linnaeus 18th century is the originator of the classification system predominantly used today even though he did not accept the theory of evolution he gave us 1 Binomial nomenclature v polynomial 2 Hierarchical classifications groups nested with groups v non hierarchical classification Example Phylum Mollusca Class Bivalvia Order Unionda Superfamily Unionidea Family Uniondae Subfamily Lampsillinae Genus Lampsillis Species L Cardium Linnaeus also gave us characteristics 3 Taxa that were defined v diagnosed by the presence are particular important Example Class Bivalvia defined by the presence of two valves shells However the word defines implies a non evolutionary world Another example if a mollusk has two shells it is a bivalve but the same species within the Molluscan class Gastropoda snails one shell and slugs no shell have evolved two shells See PDF example Are these animals properly members of the Class Gastropoda or Class Bivalvia o Linnaeus would have said Bivalvia A modern evolutionary scientist would say it belongs to the Class Gastropoda o Why The evolutionary biologist realizes that organismal lineages are mutable can change over time o Because the two valved gastropods is more closely related to other gastropods than to bivalves based on an evolution of all characteristics rather than only the o Therefore we do not define species or higher taxa we diagnose them allows for o Species interpreted as historical entities each species had a unique origin and has o Particular organisms belong in a particular species because they are part of a genealogical nexus of ancestor descendent relationships not because they possess shell descent with modification a restricted distribution any essential of defining trait etc all are historical entities o The same idea applies to higher taxa such as taxonomic classes orders genera Example Phylum Mollusca a key characteristic is the presence of a radula file like rasping feeding organ The seven extant Mollusk Classes Bivalvia clams mussels Gastropoda snails slugs Cephalopoda squid octopus Polyplacophora chitons Monoplacophora single shell Scaphopoda tusk shells Problem bivalves have no radula Aplacophora no shell worm like shape solenogasters If Phylum Mollusca was defined by radula then bivalves by definition would not be mollusks however if we view the higher taxon Mollusca as a historical entity mutable held together by a genealogical nexus of ancestor dependent relationships then the lack of a radula does not exclude Bivalvia front he Phylum Mollusca Systematic evolutionary pattern analysis philosophies o Distinction between classification and phylogeny Phylogeny a hypothesis of the evolutionary relationships among a group of organisms represented by a branching diagram phylogenetic tree Artificial Classification a classification structured for convenience does not necessarily reflect phylogeny Natural Classification a hierarchical classification based on a hypothetical phylogenetic relationships such that members of each category in the classification share a single common ancestor Three Predominant Schools of Systematics 1 Evolutionary Systematics Ernst Mayr G G Simpson a Actually been in use for hundreds of years b Uses important traits to evaluate Evolutionary history arbitrary c No explicit algorithm for generating trees ca artsy technique passed on from d Believed that both cladogenesis and anagensis be incorporated into classification expert to student schemes Cladogenesis a branching type of Evo Process involving the splitting of lineages speciation Anagenesis descent with modification with a lineage