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Basic Evolutionary Concepts Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Clown, Fool, or Simply Well Adapted? • All organisms have evolutionary adaptations – Inherited characteristics that enhance their ability to survive and reproduce • The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment – Large, webbed feet help propel the bird through water at high speeds Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – A streamlined shape, large tail, and nostrils that close are useful for diving – Specialized salt-secreting glands manage salt intake while at sea Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings EVIDENCE OF EVOLUTION 13.1 A sea voyage helped Darwin frame his theory of evolution • Aristotle and the Judeo-Christian culture believed that species are fixed • Fossils suggested that life forms change – This idea was embraced by Lamarck in the early 1800s Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed – similarities between living and fossil organisms – the diversity of life on the Galápagos Islands, such as blue-footed boobies and giant tortoises Figure 13.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The voyage of the Beagle Great Britain Europe North America Pacific Ocean Atlantic Ocean Africa Galápagos Islands Equator South America Australia Cape of Good Hope Tasmania Cape Horn Tierra del Fuego New Zealand Figure 13.1B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin became convinced that the Earth was old and continually changing – He concluded that living things also change, or evolve over generations – He also stated that living species descended from earlier life-forms: descent with modification Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.2 The study of fossils provides strong evidence for evolution • Fossils and the fossil record strongly support the theory of evolution. Incomplete but valuable, preserves only hard tissues – Hominid skull – Petrified trees Figure 13.2A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Ammonite casts – Fossilized organic matter in a leaf Figure 13.2C, D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Scorpion in amber – “Ice Man” Figure 13.2E, F Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The fossil record shows that organisms have appeared in a historical sequence • Many fossils link early extinct species with species living today – These fossilized hind leg bones link living whales with their land-dwelling ancestors Figure 13.2G, H Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.3 A mass of evidence validates the evolutionary view of life • Other evidence for evolution comes from – Biogeography: impact of geographic barriers and continental drift – Comparative anatomy and embryology – analogous and vestigal structures Human Cat Whale Bat Figure 13.3A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Molecular biology: examines similarities between molecules, estimates divergence Human Rhesus monkey Last common ancestor lived 26 million years ago (MYA), based on fossil evidence Mouse Chicken Frog Lamprey 80 MYA 275 MYA 330 MYA 450 MYA Figure 13.3B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DARWIN’S THEORY AND THE MODERN SYNTHESIS 13.4 Darwin proposed natural selection as the mechanism of evolution through differential reproduction • Darwin observed that – Reproduction: organisms produce more offspring than the environment can support – Variation: organisms vary in many characteristics – Inheritance: these variations can be inherited Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted • Darwin saw natural selection as the basic mechanism of evolution – As a result, the proportion of individuals with favorable characteristics increases – Populations gradually change in response to the environment Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment – This is called artificial selection – Example of artificial selection in plants: five vegetables derived from one species: wild mustard Figure 13.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Example of artificial selection in animals: dog breeding German shepherd Yorkshire terrier English springer spaniel Mini-dachshund Golden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 13.4B • These five canine species evolved from a common ancestor through natural selection African wild dog Coyote Fox Wolf Jackal Thousands to millions of years of natural selection Ancestral canine Figure 13.4C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.5 Connection: Scientists can observe natural selection in action • Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms – Example: camouflage adaptations of mantids that live in different environments Figure 13.5A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The evolution of insecticide resistance is an example of natural selection in action Insecticide application Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Figure 13.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.7 Microevolution is change in a population’s gene pool over time • A gene pool is the total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.11 There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance – Genetic drift can result in the bottleneck effect Original population Bottlenecking event Surviving population Figure 13.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – or the founder effect Figure 13.11B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Gene flow can change a gene pool due to the movement of genes into or out of a population • Mutation changes alleles • Natural selection leads to differential reproductive success Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.12 Adaptive change results when natural selection upsets genetic equilibrium • Natural selection results in the accumulation of traits that adapt a population to its environment – If the environment should change, natural selection would favor traits adapted to the new conditions Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.16 Not all genetic variation may be subject to natural selection • Some variations may be neutral, providing no apparent advantage or disadvantage – Example: human fingerprints Figure 13.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.17 Connection: Endangered species often have reduced variation • Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment – Studies have shown that cheetah populations exhibit extreme genetic uniformity – Thus they may have a reduced capacity to adapt to environmental challenges Figure 13.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.18 The perpetuation of genes defines evolutionary fitness • An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals • Production of fertile offspring is the only score that counts in natural selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.20 Sexual selection may produce sexual dimorphism • Sexual selection leads to the evolution of secondary sexual characteristics – These may give individuals an advantage in mating Figure 13.20A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.22 Connection: The evolution of antibiotic resistance in bacteria is a serious public M health concern • The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria – Example: Mycobacterium tuberculosis Figure 13.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • One example of rapid evolution occurred among mosquitoes who migrated into the London underground • In less than 150 years, Culex pipiens evolved into a new mosquito species, Culex molestus • The origin of new species is called speciation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The isolated mosquitoes adapted to their new underground environment – They altered their prey, mating habits, and breeding patterns • Environmental barriers that isolate populations are just one of many mechanisms in the evolution of species Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings MECHANISMS OF SPECIATION 14.3 Geographic isolation can lead to speciation • When a population is cut off from its parent stock, species evolution may occur – An isolated population may become genetically unique as its gene pool is changed by natural selection, genetic drift, or mutation – This is called allopatric speciation Figure 14.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 14.4 Islands are living laboratories of speciation • On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.4A 14.5 New species can also arise within the same geographic area as the parent species • In sympatric speciation, a new species may arise without geographic isolation – A failure in meiosis can produce diploid gametes – Self-fertilization can then produce a tetraploid zygote Parent species Zygote Meiotic error Selffertilization 2n = 6 Diploid Offspring may be viable and self-fertile 4n = 12 Tetraploid Unreduced diploid gametes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.5A 14.6 Connection: Polyploid plants clothe and feed us • Many plants are polyploid – They are the products of hybridization – The modern bread wheat is an example Figure 14.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary Tree Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Historical Time Line Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings One Possible Human Genealogy Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ancestors • Australopithecus afarensis: upright primate, vegetarian, sexual dimorphism, 4-5 million years ago • Homo habilis: first tool maker, enlarged brain, omnivore, decline in sexual dimorphism, 2.6 million years ago • Homo erectus: more brain enlargement, longer infancy, continued decline in sexual dimorphism, continued tool development, continued social development, spread out of Africa to Europe and Asia, 2 million years ago • Homo neanderthalensis: may be an extinct branch • Homo sapien: only surviving Homo species, 100,000 to 140,000 years ago Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Racial Differences • Racial differences are slight differences in phenotypes between subgroups of a common species • Advantages – Dark skin: protection from ultraviolet (UV) damage in intensive sunlight – Light skin: allows adequate UV radiation for Vitamin D production in less intense sunlight Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings