Historical Context Organisms are unchanging Aristotle & Old Testament Georges Cuvier (1812) extinctions happen. The older the life form, the more different to current version. Hutton and Lyell: geological features are produced gradually over vast time scales Lamark proposes organisms change through use and disuse and inheretance of acquired characteristics Wallace proposes a “natural selection” mechanism © 2014 Pearson Education, Inc. Figure 22.2 1809 Lamarck publishes his hypothesis of evolution. 1798 Malthus publishes “Essay on the Principle of Population.” 1795 Hutton proposes his principle of gradualism. Sketch of a flying frog by Wallace 1812 Cuvier publishes his extensive studies of vertebrate fossils. 1830 Lyell publishes Principles of Geology. 1858 While studying species in the Malay Archipelago, Wallace (shown above in 1848) sends Darwin his hypothesis of natural selection. 1790 1870 1809 Charles Darwin is born. 1831–1836 Darwin travels around the world on HMS Beagle. Marine iguana in the Galápagos Islands © 2014 Pearson Education, Inc. 1859 On the Origin of Species is published. 1844 Darwin writes his essay on descent with modification. Artificial Selection, Natural Selection, and Adaptation Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection Darwin drew two inferences from two observations © 2014 Pearson Education, Inc. Figure 22.UN03 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals. Selection & differential reproduction and Over time, favorable traits accumulate in the population. © 2014 Pearson Education, Inc. Adaptive evolution Evolution explains: The unity of life Why there is so much underlying similarities in apparently different organisms The diversity of life Why there are so many different types of living thing The match between organisms and their environment (adaptations) © 2014 Pearson Education, Inc. Figure 22.13 Results 10 Number of individuals Field Study Soapberry bug with beak inserted in balloon vine fruit © 2014 Pearson Education, Inc. 8 6 4 On native species, balloon vine (southern Florida) Beak 2 0 Average for museum specimens 10 On introduced species, goldenrain tree (central Florida) 8 6 4 2 0 6 7 8 9 Beak length (mm) 10 11 Figure 22.10 © 2014 Pearson Education, Inc. Natural selection does not create new traits, but edits or selects for traits already present in the population The current, local environment determines which traits will be selected for or selected against in any specific population © 2014 Pearson Education, Inc. Modern Synthesis aka neo-darwinism Modern Synthesis = darwin’s natural selection + modern genetics © 2014 Pearson Education, Inc. Microevolution is a change in allele frequencies in a population over generations Three mechanisms cause allele frequency change • Natural selection (including sexual selection) • Produces consistent adaptive evolution • Genetic drift • Gene flow • Artificial selection © 2014 Pearson Education, Inc. Definitions A population is a localized group of individuals capable of interbreeding and producing fertile offspring A gene pool consists of all the alleles for all loci in a population Gene a segment of DNA coding for an RNA/protein Allele different versions of a gene © 2014 Pearson Education, Inc. Effects of Genetic Drift: A Summary 1. 2. 3. 4. Genetic drift is significant in small populations Genetic drift can cause allele frequencies to change at random Genetic drift can lead to a loss of genetic variation within populations Genetic drift can cause harmful alleles to become fixed © 2014 Pearson Education, Inc. Gene Flow Gene flow consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) Gene flow tends to reduce variation among populations over time can be adaptive or not © 2014 Pearson Education, Inc. Figure 23.12 Central population NORTH SEA N Eastern population Vlieland, the Netherlands Parus major Population in which the surviving females eventually bred 40 Central Eastern 30 Survival rate (%) 50 20 10 0 © 2014 Pearson Education, Inc. Females born in Females born in central population eastern population 2 km Frequency of individuals Figure 23.13 Original population Original Evolved population population Phenotypes (fur color) (a) Directional selection (b) Disruptive selection © 2014 Pearson Education, Inc. (c) Stabilizing selection Sexual Selection Sexual selection is natural selection for mating success It can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics © 2014 Pearson Education, Inc. Why Natural Selection Cannot Fashion Perfect Organisms 1. 2. 3. 4. Selection can act only on existing variations Evolution is limited by historical constraints Adaptations are often compromises Chance, natural selection, and the environment interact © 2014 Pearson Education, Inc.