Transcript Evolution
Evolution Change over time; the process by which modern organisms have descended from ancient organisms Evolutionary history • • • • • Linnaeus: taxonomy Hutton: gradualism Lamarck: evolution Malthus: populations Cuvier: paleontology • • • • Lyell: uniformitarianism Darwin: evolution Mendel: inheritance Wallace: evolution Darwin’s Voyage Charles Darwin – “The Father of the Theory of Evolution” 1809-1882 Evolution • Evolution: the change over time of the genetic composition of populations • Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) • Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction November 24, 1859 H.M.S. Beagle • Sailed around the world in 1831 • Darwin began to make observations about the species in the world Darwin’s Observations • An enormous number of species inhabit the earth • Organisms are well suited to their environment • Organisms have many ways to survive and produce offspring Where Organisms Live • Certain organisms live in some areas but not others – Rabbits and Kangaroos live in the same type of environment – Australia has Naturally Kangaroos but not Rabbits – England has Rabbits but not Kangaroos Fossils • Some fossils look like organisms that are alive today • Other fossils look unlike any creature Darwin had ever seen • Why do species disappear? • How are organisms in fossils related to living species? Galapagos Island • Islands are close together with very different climates • Darwin saw finches with different shaped beaks on different islands • Could similar organisms on different islands once have been members of the same species? Seeds Cactus Fruit Insects Darwin’s finches • Darwin’s conclusions – small populations of original South American finches landed on islands • variation in beaks enabled individuals to gather food successfully in the different environments – over many generations, the populations of finches changed anatomically & behaviorally • accumulation of advantageous traits in population • emergence of different species Essence of Darwin’s ideas • Natural selection – variation exists in populations – over-production of offspring • more offspring than the environment can support – competition • for food, mates, nesting sites, escape predators – differential survival • successful traits = adaptations – differential reproduction • adaptations become more common in population Evolution is: Descent with Modification • Each living species has descended, with changes, from other species over time • Populations evolve over many generations Types of Evolution • Convergent evolution-two different lineages evolve similar traits – Dolphins & fishes – Wings of bees & bats • Divergent evolution-a lineage splits to have organisms with different traits – Darwin’s finches – Adaptive radiation CONVERGENT EVOLUTION Parallel Evolution • Convergent evolution in common niches – filling similar ecological roles in similar environments, so similar adaptations were selected – but are not closely related marsupial mammals placental mammals How fast does evolution occur? • Gradualism – Species change slowly over time • Punctuated Equilibrium – Species can make rapid “leaps” in evolution • Modern Synthesis – Parts of both are correct Evolution evidence: Biogeography • Geographical distribution of species • Examples: Islands vs. Mainland Australia vs. Continents Fossils • Scientists have used the fossil record to construct a history of life on Earth. – Earth’s life forms appeared 3.5 billion years ago – Fossil indicate that life forms have change over time Evolutionary change in horses 550 500 Body size (kg) 450 Equus 400 350 300 250 Merychippus 200 150 Mesohippus Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 0 Millions of years ago Evolution of birds • Archaeopteryx – lived about 150 mya – links reptiles & birds Smithsonian Museum, Washington, DC 2006 Fossil Discovery of Early Tetrapod • Tiktaalik – “missing link” from sea to land animals Anatomy – Homologous Structures - different organisms sharing similar structures from the same evolutionary origin Anatomy – Analogous Structures – different organisms sharing the same structure to perform similar functions from different evolutionary origins (evolved twice) Anatomy • Vestigial Structures – structures that have lost their function through evolution • They once had a purpose Embryology • Embryos of many organisms are alike in early stages of development. • These similarities suggest that we are all related, but have developed differences DNA AND MOLECULAR BIOLOGY • Organisms that are closely related should have similar DNA • Similar DNA indicates sharing a common ancestor at one time. Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Molecular Biology DNA & proteins are a molecular record of evolutionary relationships Comparative hemoglobin structure Human Macaque 8 Dog Bird Frog Lamprey 32 45 67 125 0 10 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans