BOOK NOTES TEST 1 BIOL1108 Mechanisms of Evolutionary Change pp 501 513 24 4 Speciation can occur rapidly or slowly and can result from changes in few or many genes Speciation is the evolutionary process by which new biological species arise The Time Course of Speciation Punctuated equilibria describes the periods of non change punctuated by sudden change Punctuated patterns indicate that speciation occurred relatively rapidly However a change over a time period such as 50 000 years short in geologic terms in a species that lived 5 million years cannot be seen in the fossil record Other species change gradually over time We still can not see the species change because reproductive isolation can not be Speciation Rates fossilized The punctuated pattern suggests that once speciation begins it can be completed fairly fast New species can arise rapidly once divergence begins Millions of years may pass before a newly formed species will itself give rise to another new species Speciation begins only after gene ow is interrupted by environmental conditions or unpredictable events Studying the Genetics of Speciation In a few cases A change in a single gene causes the evolution of reproductive isolation ex monkey owers g 24 20 pg 504 9th In other organisms the speciation process is in uenced by larger numbers of genes Studies suggest that few or many genes in uence the evolution of reproductive isolation and ex fruit y pg 504 hence the emergence of new species From Speciation to Macroevolution Speciation begins with small changes that eventually lead to much different groups than their When one group grows larger another group could become smaller due to predators Cumulative effects of speciation help to shape macroevolution that are evident in the fossil ancestors records Chapter 22 Descent with Modi cation Mechanisms of Evolutionary Change Galapagos Islands Geographical Separation of Species Darwin s Focus on Adaption environments Galapagos Finches characteristics of organisms that enhance their survival and reproduction in speci c Cactus eater insect eater seed eater all had beak variations or adaptations over time Natural Selection a process in which individuals with certain inherited traits leave more offspring than individuals with other traits BOOK NOTES TEST 1 BIOL1108 The Origin of Species Darwin Darwin developed two main ideas that descent with modi cation explain s life s unity and diversity and that natural selection brings about the match between organisms and their environment Descent with Modi cation all organisms descended from an ancestor that lived in the remote past As the ancestral organism lived in various habitats over the years it changed and adapted to meet its speci c needs Evolutionary Trees where each fork represents a common ancestor Arti cial Selection Natural Selection and Adaptation Darwin proposed Natural Selection to explain the observable patterns of evolution Arti cial Selection humans have modi ed other species over many generations in order to produce desired traits by selecting and breeding certain individuals e g crops livestock etc Darwin s Observations Inferences from Nature Observation 1 Members of a population often vary in their traits Observation 2 Traits are inherited from parents to offspring Observation 3 All species are capable of producing more offspring than their environment can support Observation 4 Owing to lack of food or other resources many of those offspring do Inference 1 Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than not survive other individuals Inference 2 This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations BOOK NOTES TEST 1 BIOL1108 Natural Selection A Summary Natural selection is a process in which individuals that have certain heritable characteristics survive and reproduce at a higher rate than other individuals Over time natural selection can increase the match between organisms and their environment In an environment changes or if individuals move to a new environment natural selection may result in adaptation to these new conditions sometimes giving rise to new species in the process Individuals DO NOT evolve but populations over time Natural Selection only in uences HERITABLE genes Environmental factors vary from place to place and over time 22 3 Direct Observations of Evolutionary Change 1 A Change in the food source of a population BOOK NOTES TEST 1 BIOL1108 2 A Spread of Drug Resistant Bacteria mRSA Methicillin resistant S aureus BOOK NOTES TEST 1 BIOL1108 Bacteria contained enzyme penicillinase that destroyed penicillin so scientists developed methicillin which bacteria also eventually developed resistance to Methicillin works by deactivating a protein that bacteria use to synthesize their cell wall Resistant peoples used other protein to synthesize bacterial cell wall that was not affected by methicillin antibiotic These multiple strains of the bacteria are able to transfer genetic information over the years allowing for multi antibiotic resistant forms of the bacteria to exist These two examples highlight two important points about Natural Selection Does not create individuals but selects them randomly depending on time and place 3 Fossil Record Record shows us many organisms have become extinct Also shows evolutionary changes that have occurred over time in groups of organisms Ex Fig 22 16 The transition to life in the sea fossil record shows origin of a major new group of mammals cetaceans and how they transitioned from land to sea 4 Homology analyzing similarities between different animals Characteristics that were in an ancestral organism were modi ed to t their environment over time Homologous Structures represent variations on a structural theme that was present in their common ancestor elements e g mammalian forelimbs even though they have become adapted for different functions the forelimbs of all mammals are constructed from the same basic skeletal Vestigial Structures remnants of features or leftover structures that served important functions in the organisms ancestors BOOK NOTES TEST 1 BIOL1108 ancestors organisms forms a nested pattern ex skeletons of some snakes retain vestiges of the pelvis and leg bones of walking Evolutionary Tree a diagram that re ects evolutionary relationships among groups of