Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Lectures by Chris C. Romero PowerPoint ® Lectures for Essential Biology, Third Edition – Neil Campbell, Jane Reece, and Eric Simon Essential Biology with Physiology, Second Edition – Neil Campbell, Jane Reece, and Eric Simon CHAPTER 13 How Populations Evolve

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings EVOLUTION - a change over time in the genetic composition of a population driven by natural selection. The basic idea of natural selection is that –Organisms can change over generations. –Individuals with certain favorable heritable traits leave more offspring than others.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Evolution trends 1.Convergent evolution – unrelated species evolve in similar ways. Same environmental pressure produces similar adaptation. Exp. Animals that fly. 2.Divergent evolution – population splits into a new species to better suit their environment. 1.Allopatric speciation 2.Sympatric speciation 3.Parallel evolution – species that separated for a very long time but still evolve independently maintaining similar traits 4.Co-evolution – close interactive species (birds & flowers) exert selective pressure so they evolve together

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Darwin made two main points in The Origin of Species: –Organisms today came from ancestral species and natural selection was the mechanism for descent with modification.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings A. Evidence 1.Fossils - remnants or impressions left by organisms that lived in the past. 2.The fossil record & sedimentary rock –The fossil record is the ordered sequence of fossils as they appear in rock layers in history.

Figure 13.7

Figure 13.8

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Evidence continues 3.Comparative anatomy – comparing body structure between different species. 4.Homology - similarity in structures due to common ancestry. a)Fore limbs of human, cats, whales, and baths b)Vestigial organs – structures that have no importance to a living organisms but did in the organisms’ ancestor. 5.Comparative embryology is the comparison of structures that appear during the development of different organisms.

Figure 13.11

Figure 13.12

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Evidence Continues 6.Molecular Biology – similarities when comparing DNA and proteins in different organisms.

Figure 13.13

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Three General Outcomes of Natural Selection 1.Directional selection – favor extreme phenotype. 2. Disruptive selection - Can lead to a balance between two or more contrasting morphs in a population. 3. Stabilizing selection - Maintains variation for a particular trait within a narrow range. 4. Sexual selection – pea cock: look good=good genes

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings B. Natural Selection in Action Examples of natural selection include –Pesticide resistance in insects. –The development of antibiotic-resistant bacteria. –Drug-resistant strains of HIV.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings C. Sources of Genetic Variation 1.Mutations - changes in the DNA of an organism. 2.Sexual recombination - Shuffles alleles during meiosis.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings D. Speciation 1.Species – a population of organisms that can interbreed (mate, reproduce) 2.Speciation – the creation of new species 1.Allopatric – new species created due to geographical isolation (mountain ranges, water, etc). 2.Sympatric – no geographic isolation but a new species is created due to random mating and changes in the chromosome set number. 1.2 sets of chromosomes to 3 sets. the 2 organisms can no longer interbreed. Most common in plants. Polyploidy.