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Evolutionary view of life 陳嘉祥, MD, Ph.D. 林口長庚醫院精神科 長庚大學生物醫學系 Evolution accounts for the unity and diversity of life “Nothing in biology makes sense except in the light of evolution” -Theodosius Dobzhansky 1900-1975 Traditional view • The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae • The Old Testament holds that species were individually designed by God and therefore perfect • Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose Figure 22.2 1809 Lamarck publishes his hypothesis of evolution. 1798 Malthus publishes “Essay on the Principle of Population.” 1812 1858 Cuvier publishes his extensive studies of vertebrate fossils. 1795 Hutton proposes his principle of gradualism. 1830 Lyell publishes Principles of Geology. While studying species in the Malay Archipelago, Wallace sends Darwin his hypothesis of natural selection. 1790 1809 183136 Charles Darwin is born. Darwin travels around the world on HMS Beagle. 1870 1859 On the Origin of Species is published. 1844 Darwin writes his essay on descent with modification. The Galápagos Islands Figure 22.3 Sedimentary rock layers (strata) Younger stratum with more recent fossils Older stratum with older fossils The Fossil Record • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time © 2011 Pearson Education, Inc. Video: Grand Canyon © 2011 Pearson Education, Inc. Ideas About Change over Time • The study of fossils helped to lay the groundwork for Darwin’s ideas • Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata • Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier • Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe © 2011 Pearson Education, Inc. Lamarck’s Hypothesis of Evolution • Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics © 2011 Pearson Education, Inc. Figure 22.5 Darwin in 1840, after his return from the voyage HMS Beagle in port Great Britain EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA PACIFIC OCEAN Pinta Genovesa Santiago Fernandina Isabela 0 20 40 Kilometers Daphne Islands Pinzó n Santa Santa Cruz Fe Florenza Equator SOUTH AMERICA Equator Chile PACIFIC OCEAN San Cristobal Españ ola Andes Mtns. Marchena Brazil Malay Archipelago PACIFIC OCEAN AUSTRALIA Cape of Argentina Good Hope Cape Horn Tasmania New Zealand The Voyage of the Beagle • During his travels on the Beagle, Darwin collected specimens of South American plants and animals • He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions • He experienced an earthquake in Chile and observed the uplift of rocks © 2011 Pearson Education, Inc. Figure 22.5c The Galápagos Islands PACIFIC OCEAN Pinta Genovesa Marchena Santiago Fernandina Isabela 0 20 40 Kilometers Equator Daphne Islands Pinzó n Santa Santa Cruz Fe Florenza San Cristobal Españ ola Video: Galápagos Islands Overview © 2011 Pearson Education, Inc. Video: Blue-footed Boobies Courtship Ritual © 2011 Pearson Education, Inc. Video: Albatross Courtship Ritual © 2011 Pearson Education, Inc. Video: Galápagos Sea Lion © 2011 Pearson Education, Inc. Video: Soaring Hawk © 2011 Pearson Education, Inc. Video: Galápagos Tortoises © 2011 Pearson Education, Inc. Video: Galápagos Marine Iguana © 2011 Pearson Education, Inc. Darwin’s Focus on Adaptation • In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes • In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification, but did not introduce his theory publicly • Natural selection is a process in which individuals with favorable inherited traits are more likely to survive and reproduce The origin of Species • In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s • Darwin quickly finished The Origin of Species and published it the next year Alfred Russel Wallace • • • • • 1823-1913 Co-discovery of natural selection Pioneering work on biogeography Wallace Line Wallace effect Biogeography Frontispiece to Alfred Russel Wallace's book The Geographical Distribution of Animals Wallace line Wallace effect • Natural selection can contribute to the reproductive isolation of incipient species by evolving barriers against hybridization. • When two varieties of a species had diverged beyond a certain point, each adapted to different conditions, hybrid offspring would be less well adapted than either parent form. At that point natural selection will tend to eliminate the hybrids. The Origin of Species • Darwin explained three broad observations: – The unity of life – The diversity of life – The match between organisms and their environment © 2011 Pearson Education, Inc. • Observation #1: Members of a population often vary in their inherited traits © 2011 Pearson Education, Inc. Figure 22.10 Figure 22.6 (b) Insect-eater (a) Cactus-eater (c) Seed-eater Figure 22.5c The Galápagos Islands PACIFIC OCEAN Pinta Genovesa Marchena Santiago Fernandina Isabela 0 20 40 Kilometers Equator Daphne Islands Pinzó n Santa Santa Cruz Fe Florenza San Cristobal Españ ola The Beak of the Finch: A Story of Evolution in Our Time • Johnathan Weiner, Pulitzer Prize for General Non-Fiction in 1995 • Peter and Rosemary Grant • 1973- 2005 Balzan Prize for Population Biology • "Peter and Rosemary Grant are distinguished for their remarkable long-term studies demonstrating evolution in action in Galápagos finches. They have demonstrated how very rapid changes in body and beak size in response to changes in the food supply are driven by natural selection. They have also elucidated the mechanisms by which new species arise and how genetic diversity is maintained in natural populations. The work of the Grants has had a seminal influence in the fields of population biology, evolution and ecology." Descent with Modification • Darwin never used the word evolution in the first edition of The Origin of Species • The phrase descent with modification summarized Darwin’s perception of the unity of life • The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past © 2011 Pearson Education, Inc. Herbert Spencer • 1820-1903, Philosopher, biologist, anthropologist, sociologist, classical liberal political theorist, polymath • Evolution • Survival of the fittest • (Striving for the best) • Social Darwinism • Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals © 2011 Pearson Education, Inc. • Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce © 2011 Pearson Education, Inc. Figure 22.11 Spore cloud • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations © 2011 Pearson Education, Inc. Thomas Robert Malthus An Essay on the Principle of Population 1766-1834 1. That the increase of population is necessarily limited by the means of subsistence, 2. That population does invariably increase when the means of subsistence increase, and, 3. That the superior power of population is repressed, and the actual population kept equal to the means of subsistence, by misery and vice. • Darwin was influenced by Thomas Malthus, who noted the potential for human population to increase faster than food supplies and other resources • If some heritable traits are advantageous, these will accumulate in a population over time, and this will increase the frequency of individuals with these traits • This process explains the match between organisms and their environment © 2011 Pearson Education, Inc. Evolution by natural selection • It is a process inferred from three facts about populations – more offspring are produced than can possibly survive – traits vary among individuals, leading to different rates of survival and reproduction – trait differences are heritable • This process creates and preserves traits that are seemingly fitted for the functional roles they perform Fitness • A potential for an individual to survive and reproduce (a function of its reproductive success or the number of the reproducing offspring it produces) under certain selection conditions. Natural Selection: A Summary • Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals • Natural selection increases the adaptation of organisms to their environment over time • If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species © 2011 Pearson Education, Inc. Inheritance and variation Gregor Mendel 1822-1884 August Weismann Hugo de Vries 1834-1914 1848-1935 Germ cell Mutation Debate of two schools (1900-1915) • Saltationism (large mutations or jumps), favored by early Mendelians who viewed hard inheritance as incompatible with natural selection. • Biometric school: led by Karl Pearson and Walter Weldon, argued vigorously against it, saying that empirical evidence indicated that variation was continuous in most organisms, not discrete as Mendelism predicted. Modern evolutionary synthesis • is a 20th-century union of ideas from several biological specialties which provides a widely accepted account of evolution • produced between 1936 and 1947, reflects the consensus about how evolution proceeds • The previous development of population genetics, between 1918 and 1932, was a stimulus. • The synthesis is still, to a large extent, the current paradigm in evolutionary biology Population genetics-1 • R.A. Fisher: – the continuous variation measured by the biometricians could be the result of the action of many discrete genetic loci – how Mendelian genetics was, contrary to the thinking of many early geneticists, completely consistent with the idea of evolution driven by natural selection Population genetics-2 • J.B.S. Haldane, – applied mathematical analysis to real world examples of natural selection such as the evolution of industrial melanism in peppered moths – established that natural selection could work in the real world at a faster rate than even Fisher had assumed Population genetics-3 • Sewall Wright, – introduced the concept of an adaptive landscape in which phenomena such as cross breeding and genetic drift in small populations could push them away from adaptive peaks, which would in turn allow natural selection to push them towards new adaptive peaks Summary of modern evolutionary synthesis-1 • All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists. • Evolution is gradual: small genetic changes regulated by natural selection accumulate over long periods. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction. Summary of modern evolutionary synthesis-2 • Natural selection is by far the main mechanism of change. The object of selection is the phenotype in its surrounding environment. • Thinking in terms of populations, rather than individuals, is primary: the genetic diversity existing in natural populations is a key factor in evolution. Summary of modern evolutionary synthesis-3 • In palaeontology, the ability to explain historical observations by extrapolation from microevolution to macroevolution is proposed. Historical contingency means explanations at different levels may exist. Gradualism does not mean constant rate of change. Refinement of modern evolutionary synthesis • The synthesis as it exists now has extended the scope of the Darwinian idea of natural selection to include subsequent scientific discoveries and concepts unknown to Darwin, such as DNA and genetics. Gene-centered view of evolution • The Selfish Gene: Richard Dawkins • Since heritable information is passed from generation to generation by genetic material, natural selection and evolution are best considered from the perspective of genes. • Genes whose phenotypic effects successfully promote their own propagation will be favorably selected in detriment to their competitors. 基因與個体間的関係 DNA 在生殖的過程中 完成複製. Organism 身體是DNA的載具,它 所有的作為都是在保 存並散播DNA。 Punctuated equilibrium • 1972: Stephen Jay Gould and Niles Eldredge • selective pressures were heightened, punctuating long periods of morphological stability, as welladapted organisms coped successfully in their respective environments. Punctuated equilibrium Stasis vs Cladogenesis Evolution by artificial selection Cabbage Selection for apical (tip) bud Brussels sprouts Selection for axillary (side) buds Broccoli Selection for flowers and stems Selection for stems Selection for leaves Kale Wild mustard Kohlrabi 競爭:生命中無可逃避的宿命! 食物 交配 陽光和水 生物為什會有利他的行為? 合作的好處:互利互惠! Wolves hunt in packs and then share their prey. 無私的個人與自私的基因 Parent birds feed their chick 無私的行為源自於自私的基因! Altruistic donor individual Selfish “helping” gene W.D. Hamilton (1936-2000) Kin selection Hamilton’s Rule (1964) Relatedness to partner r.B > C Benefit to partner Personal cost This rule predicts when a gene for altruism should be selected. Prediction: cooperation at high relatedness, conflict at low relatedness. The peacock’s tail Extravagant male ornaments The peacock’s tail greatly impairs his mobility…how could such a trait evolve? Why a theory of sexual selection? Darwin needed a theory to explain the many extravagant traits that seem to reduce survival e.g. the peacock’s tail Theory of Sexual Selection Darwin (1871, p256): “We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.” Intersexual Selection Fisher’s runaway model Survival Selection Sexual Selection Total male fitness (survival + mating) Fitness Female choice adaptive for survival Fitness due to survival Tail length