Common Descent with Modification Evolution and Its Core Principles. Common Descent with Modification. Natural Selection

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1 16.1 Evolution and Its Core Principles Common Descent with Modification Descent with modification A key theory of evolution Describes the process by which species of living things can undergo modification over time, with such change sometimes resulting in the formation of new, separate species Geologic time Life known to have existed for at least 3.8 billion years» stromatolites Therefore Common Descent with Modification All species on Earth have descended from other species, and a single, common ancestor lies at the base of the evolutionary tree Natural Selection Natural selection A second key principle in the theory of evolution differential adaptation of individual organisms to their environment Individuals better adapted to their CURRENT environment are more likely to survive Therefore, more likely to produce offspring and possibly pass those favorable traits on to those offspring 1

2 Importance of Evolution as a Concept The theory of evolution has an importance beyond the domain of biology. Through it, human beings have become aware that: 1. They are descended from other varieties of living things. 2. The organisms that populate the living world are not fixed entities, but instead are constantly undergoing modification Charles Darwin and the Theory of Evolution Darwin and the Theory of Evolution Darwin and the Theory of Evolution Charles Darwin deserves primary credit for the theory of evolution. Alfred Russel Wallace came up with it too Developed existing ideas about descent with modification while providing a large body of evidence in support of them. First to perceive natural selection as the primary process that drives evolution. Figure

3 Darwin and the Theory of Evolution Darwin and the Theory of Evolution 1831 voyage on the HMS Beagle insights were inspired by the research he carried out during a five-year voyage he took around the world North America Sept Galapagos Islands July 1834 South America Dec Oct Europe Africa Asia equator April 1832 Australia Jan Falkland Islands March 1833 March 1834 Figure Evolutionary Thinking before Darwin Evolutionary Thinking Before Darwin Charles Lyell Noted the dynamic geological nature of the Earth First to propose platetectonics Influenced some of Darwin s ideas Darwin noted marine snails in the Andes Mts. 3

4 Evolutionary Thinking Before Darwin Also important were Jean-Baptiste de Lamarck and Georges Cuvier. Lamarck noted the possibility of descent with modification But thought ACQUIRED traits are passed on Cuvier noted the extinction of some species on Earth and the appearance of others within different time-frames Less complex organisms replaced by more complex organisms Evolutionary Thinking Before Darwin Figure 16.5 Darwin s Insights 16.4 Darwin s Insights Following the Beagle s Voyage Darwin understood descent with modification for several years before he realized that natural selection was the most important process driving it Thomas Malthus Writings on limits to population growth sparked Darwins realization about natural selection Competition for resources Coined the phrase survival of the fittest 4

5 Alfred Russel Wallace 16.5 Alfred Russel Wallace English naturalist co-discoverer of natural selection as the principal process underlying evolution Had this idea while sick with Malaria in Indonesia in 1858 Collaborated with Darwin 16.6 Descent with Modification Is Accepted Descent with Modification is Accepted On the Origin of Species by Means of Natural Selection Published in 1859 Descent with modification was accepted by most scientists not long after Scientists accepted it because it explained so many facets of the living world 5

6 Descent with Modification is Accepted Descent with Modification is Accepted Pharyngeal slits exist in these five vertebrate animals... pharyngeal slits sea lamprey pond turtle chicken domestic cat human being... evidence that all five evolved from a common ancestor Figure 16.7 Figure 16.9 Controversy over Natural Selection 16.7 Darwin Doubted: The Controversy over Natural Selection natural selection as the most important process underlying evolution not generally accepted (by non-scientists) until the middle of the twentieth century 6

7 Controversy over Natural Selection Widespread acceptance of natural selection hinged on a modern synthesis in the theory of evolution that brought together lines of evidence from genetics, the fossil record, and the distribution of organisms throughout the world 16.8 Opposition to the Theory of Evolution Opposition to the Theory of Evolution Even today, the theory of evolution is regularly challenged as being unproven or simply wrong. Opposition to the Theory of Evolution One factor leading to the appearance of a scientific debate over evolution is confusion about the meaning of the word theory. Though the average person may equate theory with speculation, in science a theory is a general set of principles supported by a lot of evidence that explains some aspect of the natural world. 7

8 The Evidence for Evolution 16.9 The Evidence for Evolution Six lines of evidence are consistent with the theory of evolution. 1. Radiometric Dating 2. Fossils First Radiometric (carbon) dating has confirmed the immense age of the Earth (4.6 billion) an age that is consistent with the long periods of time scientists believe it has taken species to evolve Second around the globe, fossils from the same evolutionary periods are consistently found together in geologic strata 8

9 2. Fossils Excellent agreement between the relative ages assigned to fossils by evolutionary theory and the absolute ages assigned to them by radiometric dating 3. Comparative Morphology and Embryology Third the theory of evolution explains the common occurrence of homologous physical structures in different organisms 3. Comparative Morphology and Embryology 4. Evidence from Biogeography Fourth island biogeography the geographic distribution of species on Earth s islands is explained by the theory of evolution As noted by Darwin in the Galapagos islands Bats only native mammals on isolated islands whale cat bat gorilla Figure

10 4. Evidence from Biogeography Fifth 5. Evidence from Gene Modification variations found in the DNA sequences of various organisms are consistent with evolutionary theory Organisms considered less closely related possess genomes more divergent or different from one another Figure Large number of base differences between humans and yeast Small number of base differences between humans and pigs 5. Evidence from Gene Modification Number of DNA nucleotide base differences in the cytochrome c oxidase gene human pig duck snake tuna moth yeast Sixth 6. Experimental Evidence experimental demonstrations of evolution have been carried out in the laboratory and in nature Guppies Bacterial drug resistance Figure