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Evolution Chapter 15 Outline An Introduction to Evolution A Brief Overview of the Early Development of Evolutionary Concepts Charles Darwin Evidence for Evolution Microevolution – Evolution within Species Rates of Evolution Macroevolution – How Species Evolve The Role of Hybridization in Evolution An Introduction to Evolution Natural selection - tendency of organisms with favorable adaptations to their environment to survive and produce new generations • Theory proposed by Charles Darwin, 1859, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Organic evolution - accumulation of genetic changes in populations of living organisms through many changes An Introduction to Evolution The Study of Evolutionary Biology Subdisciplines of evolutionary biology: • Behavioral evolution - study of development of behavioral traits − Mating, food gathering, social interactions, predatory-prey relationships • Evolutionary developmental biology - study of effect of genetic variation on traits that effect survival and reproduction • Evolutionary ecology - study of how ecological features (i.e., life histories and reproductive strategies) effect evolution of species and ecosystems An Introduction to Evolution The Study of Evolutionary Biology Subdisciplines of evolutionary biology cont’d.: • Evolutionary genetics - use of molecular and transmission genetics to understand origins of genetic variability • Evolutionary paleontology - use of fossil record to examine large-scale evolutionary change, including origins of lineages and changes in anatomy over time • Evolutionary physiology and morphology - study of adaptation through biochemical, physiological, and anatomical changes An Introduction to Evolution The Study of Evolutionary Biology Subdisciplines of evolutionary biology cont’d.: • Human evolution - use of all disciplines of evolution to study genetic variation in both modern and historical human populations • Molecular evolution - study of evolutionary changes in DNA in relation to gene structure, organization, and control of expression • Systematics - naming of species and determination of their evolutionary relationships An Introduction to Evolution Evolution in Agriculture Humans use artificial selection, or breeding, to change agricultural and domestic plants and animals • Evolution directed by humans Agricultural systems agents of change by influencing evolution of native species • Example: insect populations evolving resistance to insecticides An Introduction to Evolution Evolutionary Medicine Evolutionary medicine applies evolutionary principles to way in which we treat illness • Example: evolution of bacteria, obtaining genetic ability to overcome antibiotics Also applies application of evolutionary research involving discovery of natural compounds that may be useful in medicine • Can predict where to look for new products in relatives of useful plants • Can look for plants that might have undergone selection pressure for those adaptations An Introduction to Evolution Species Extinctions and Invasions Loss of species undermines health of entire ecosystems Conservation biology uses evolutionary principles to understand species expansion or contraction in response to changing environments Kudzu, and invasive plant from Japan Evolutionary biologists study species invasions • Natural selection in introduced plants, where there are no natural pests or herbivores, favors reproduction – Outcompete native vegetation An Introduction to Evolution Biotechnology and Evolution Evolutionary biologists determine fate of transgenes after genetically engineered crop plants planted in fields • Transgenes - foreign genes introduced into plants through genetic engineering • Gene exchange between crop plants and their wild relatives? − Herbicide resistant weeds A Brief Overview of the Early Development of Evolutionary Concepts Aristotle (384-322 BC) - arranged organisms from simplest to most complex = scale of nature • Implied organisms static and do not evolve Leonardo da Vinci (1452-1519) - observed fossils part of previously existing organisms now extinct Count de Buffon (1707-1788) - described all known plants and animals • Presented evidence that organisms change across generations A Brief Overview of the Early Development of Evolutionary Concepts End of 18th century many prominent biologists believed hereditary changes in populations over long periods of time occurred as result of inheritance of acquired characteristics • Jean Baptiste Lamarck (1744–1829) - characters acquired during life passed on and became cumulative Major revolutions in evolutionary thought occurred in last 150 years A Brief Overview of the Early Development of Evolutionary Concepts First revolution - Charles Darwin, Origin of Species, 1859 • Evolution by natural selection Second revolution - 1930’s • Theories of Darwinian natural selection, Mendelian genetics and population genetics intersected providing better understanding of mechanisms of evolution Third revolution - Now • Evolution of development = “Evo-devo” − Homeobox genes - regulatory genes that act as developmental switches Charles Darwin (1809–1882) Assistant naturalist on HMS Beagle to voyage around world and chart coastlines, 1831–1836 • Read Charles Lyell’s geology book, theorized earth much older than previously believed • Collected plants and animals in South America, Galapagos Islands, Australia and New Zealand Guided by ideas of Malthus, 1798 • Populations grow geometrically until food supplies and other factors limit growth Presented joint paper on natural selection with Alfred Wallace year prior to publication of Origin of Species Evidence for Evolution Homology - characteristic shared by different organisms with common ancestry • Convergent evolution similarities not due to common ancestry − Plants of different ancestry adapted in similar ways to common environmental conditions in different parts of world Cactus and Euphorbia Evidence for Evolution Structure and relationships of proteins, DNA, and other molecules; and common use of ATP • Ex.: cytochrome c oxidase - universal in all living organisms − Suggests early, single origin Fossil Record Geographical distribution of organisms Fossil fern Microevolution – Evolution Within Species Natural Selection Darwin observed: • Artificial selection - changes in populations of domestic animals by retaining animals with desirable traits • Limited supply of food and other resources prevents some individuals from reproducing • Competitive abilities of individuals vary within populations • Comparative anatomy and embryology Reasoned individuals best adapted to utilize available resources would increase in # in succeeding generations Natural selection - descent with modification Microevolution – Evolution Within Species Natural Selection Darwin based natural selection on: – Overproduction of offspring – Struggle for existence - competition for resources – Inheritance and accumulation of favorable variations – Survival and reproduction of fittest (differential survival and reproduction) Criticism of natural selection in Darwin’s time: natural selection did not explain origin of hereditary variation Microevolution – Evolution Within Species Mutation - change in gene or chromosome • Deletion - part of chromosome breaks off • Translocation - piece of chromosome becomes attached to another • Inversion - part of chromosome breaks off and reattaches in inverted position • One or more nucleotide pairs changes • Most mutations harmful; some silent or some produce characteristic that helps organism survive change A. Deletion B. Translocation C. Inversion Microevolution – Evolution Within Species Migration - gene flow between populations when individuals or gametes migrate from one population to another • Depends on size of population and extent of isolation Genetic drift - changes in genetic make-up of population due to random events Rates of Evolution Darwin believed evolution by natural selection slow and gradual Contemporary biologists believe theory of punctuated equilibrium • Major changes occurred in spurts (ca. 100,000 years) followed by millions of years with minor change • Hypothesis based on fossils - reveal large gaps in fossil record Macroevolution – How Species Evolve Geographic isolation • Isolation of two populations prevents gene flow • Random mutations spread only throughout population in which they arise • Genetic changes become so great gene flow between populations no longer occur Ecological isolation • Ecological factors such as climate or soils play role in isolation, as do time and mechanical isolating factors • Results in sympatric species that occupy overlapping ranges of territories, and do not exchange genes Macroevolution – How Species Evolve Mechanical isolation • Ex.: pollinia of orchids Other isolating mechanisms: • Sperm chemically or mechanically prevented from reaching egg • Postzygotic isolating mechanisms: − Failure of embryos to develop − Failure of hybrids to survive or breed Chromosomes may not pair normally at meiosis, resulting in sterile hybrids The Role of Hybridization in Evolution Hybrids - offspring produced by parents differing in one or more characteristics • May have gene combinations better suited to new environments • Two related species may hybridize −Introgression - intercrossing between hybrids and parents The Role of Hybridization in Evolution Polyploidy - occurrence of double normal chromosome # • Result of failure of meiosis to halve chromosome # in gametes • Polyploids produced when these gametes participate in fertilization Hybrids often sterile because chromosomes do not pair properly at meiosis • If polyploid formed in hybrid, then chromosomes can pair and overcome sterility • >50% of flowering plant species originated this way The Role of Hybridization in Evolution Sterile hybrids may reproduce asexually Apomixis - production of seeds without fertilization • Combination of apomixis and sexual reproduction may be highly successful − Dandelions Dandelion Review An Introduction to Evolution A Brief Overview of the Early Development of Evolutionary Concepts Charles Darwin Evidence for Evolution Microevolution – Evolution within Species Rates of Evolution Macroevolution – How Species Evolve The Role of Hybridization in Evolution