Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oldest multicellular fossil Oldest fossil prokaryotic cell Evolution – genetic change over time

LE 13-1b North America Great Britain ATLANTIC OCEAN PACIFIC OCEAN South America Andes Cape of Good Hope Cape Horn Tierra del Fuego Africa Europe Asia Equator PACIFIC OCEAN Australia Tasmania New Zealand The Galápagos Islands Pinta Fernandina Isabela Santiago Marchena Genovesa Daphne Islands Pinzón Santa Cruz Santa Fe San Cristobal Florenza Española Equator miles 40 km PACIFIC OCEAN

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural Selection Darwin proposed natural selection as the mechanism of evolution Organisms vary in many characteristics that can be inherited Excessive numbers of organisms lead to a struggle for survival Organisms produce more offspring than the environment can support What is a Species?

LE 13-2c African wild dogCoyoteWolfFoxJackal Thousands to millions of years of natural selection Ancestral canine Natural selection is supported by evidence from artificial selection

LE 13-4a HumanCatWhaleBat – Common embryonic structures in all vertebrates are evidence for common descent

LE 13-4b Chick embryo Pharyngeal pouches Post-anal tail Human embryo

LE 13-5b Chromosome with gene conferring resistance to pesticide Pesticide application Survivor Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Examples of evolutionary adaptation reveal three key points about natural selection – Natural selection is more of an editing process than a creative mechanism – Natural selection is contingent on time and place – Significant evolutionary change can occur in a short time

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Studying evolution at the population level – Evolution: change in the prevalence of certain heritable characteristics in a population over a span of generations – Gene pool: the total collection of genes in a population at any one time – Microevolution: a change in the relative frequencies of alleles in a gene pool – Species: a group of populations capable of interbreeding and producing fertile offspring

LE 13-9a Original population Bottlenecking event Surviving population In addition to natural selection, other events can contribute to evolution

LE 13-12a Parents Meiosis Gametes A1A1 A1A1 A2A2 A3A3  A3A3 A2A2 A1A1

LE 13-12b Fertilization Offspring, with new combinations of alleles and A1A1 A2A2 A1A1 A3A3 A3A3 A2A2 A1A1 Gametes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION The evolution of antibiotic resistance in bacteria is a serious public health concern Natural selection has led to the evolution of antibiotic-resistant bacteria Overuse and misuse of antibiotics has contributed to the proliferation of antibiotic-resistant strains – Example: tuberculosis

Neutral traits

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The perpetuation of genes defines evolutionary fitness Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation Survival of genes depends on production of fertile offspring Selection indirectly adapts a population to its environment by acting on phenotype

LE Original population Evolved population Stabilizing selection Phenotypes (fur color) Original population Frequency of individuals Directional selection Disruptive selection Natural selection can alter variation in a population

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection cannot fashion perfect organisms There are at least four reasons why natural selection cannot produce perfection – Organisms are limited by historical constraints – Adaptations are often compromises – Chance and natural selection interact – Selection can only edit existing variations

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings