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Transcript
Evolution and Biodiversity Apes Chapter 5 Darwin’s Ideas – An “evolution”, not a “revolution” Pre-darwininan ideas Species are fixed, permanent, no change Earth young – less than 10,000 years old New ideas Georges Buffon – earth much older – fossils Lamark Species changed, process of adaptation Inheritance of acquired characteristics Voyage of the Beagle 1831 Charles Darwin – 22-year old college student The Galapagos Islands – Why Important? Lyell and geology – Earth’s geological features changing over very long periods of time – Earth is OLD Results in a changing environments – living things faced with constant change Darwin Analyzes Data – And Formulates his Theory Thomas Malthus – Populations can grow much faster than food supplies, other resources – exponential growth Darwin’s interpretation – Struggle for Survival Published The Origin of Species - 1859 Darwin’s Main Points What were Darwin’s two main points? Descent with Modification Natural Selection Why is this type of rock important? Dating Fossils Sedimentary rock – relative ages Radiometric dating Half-life of radioactive elements U-238 –4.5 billion C-14 – 5600 years How does carbon get into living organisms? Accurate to 50,000 years Homologous Structures What are some similarities? How is the use of these structures different? Do you think homologous are evidence of common ancestors? Explain. Evidence - vestigial structures Evidence Similarities in embryological development Evidence in molecules of life Proteins such as hemoglobin (page 304) DNA analysis - humans and chimps - 2% difference in species Microevolution (14.4) What is a gene pool ? What is “stored” in a population’s gene pool? Microevolution – genetic changes in an organisms gene pool. Evolution acts on populations – not on individuals Changes in Gene Pools Microevolution: the frequency of alleles in a gene pool changes; evolution on the smallest scale “Ingredients” for microevolution (101) Variation within population Trait must be inherited (genetic basis) Trait must lead to differential reproduction Why Variation? Mutation – most often random Can chances be increased May not offer any advantage or disadvantage Especially important in changing gene pool in asexual, rapidly reproducing individuals Examples?? In Sexually reproducing organisms – variation also caused by: “shuffling” of different chromosomes – independent assortment Crossing over during meiosis Natural Selection Variation is always present in a population due to genetic variation (variation in gene pool of the population) What decides what individuals survive and reproduce? If organisms reproduce, genetic makeup is passed to their young! Thus, organisms that are better adapted have better chance of survival to reproductive age – and pass on genetic traits Natural Selection – Not by Chance Think of peppered moth, pesticide resistance, AIDS This selection leads to adaptations Is a favorable adaptation always remain a favorable adaptation? EXPLAIN Snail coloration best adapted to conditions Average Natural selection Number of individuals Number of individuals Directional Natural Selection New average Coloration of snails Average shifts Coloration of snails Proportion of light-colored snails in population increases Figure 5-6 (1) Page 102 Previous average Intermediate-colored snails are selected against Light coloration is favored Dark coloration is favored Natural selection Number of individuals Number of individuals Diversifying Natural Selection Coloration of snails Coloration of snails Number of individuals with light and dark coloration increases, and the number with intermediate coloration decreases Figure 5-6 (3) Page 102 Snails with light and dark colors dominate Peppered Moth – directional microevolution Evolution of antibiotic resistance Drug kills most bacteria Survivors reproduce quickly – develop resistant population What Else can cause changes in Gene Pool? Chance changes in allele frequency - no selection for advantageous traits Genetic Drift 1. Bottleneck Effect 2. Founder Effect Gene Flow Mutation Founder Effect Small population migrates to a location Limited gene pool Population may differ from original population Gene Flow Migration of organisms from “outside” populations Artificial Selection Humans act as environment - choose those genetic traits that will survive What are some factors that “replace” humans in natural selection? Coevolution Interaction between species results in microevolution in both species populations Predator-prey Symbiosis – may be much more important than proposed by Darwin Convergent evolution Are similar structures always evidence of evolutionary relationships? •NO!! Consider - animals that eat insects Called analogous structures Examples Convergent Evolution (from PBS website) Convergent Evolution Are these homologous structures? Why or why not? Ecological Niches and Adaptation (103) Niche – species “way of life” or functional role in ecosystem Range of tolerance for physical/chemical conditions Resources it uses Interactions Role in food webs/energy cycling Habitat Functional niche vs realized niche Number of individuals Generalist vs. Specialist Niche separation Generalist species with a narrow niche Niche breadth Generalist species with a broad niche Region of niche overlap Resource use Figure 5-7 Page 104 What are examples of generalist vs. specialist species? Why not a superorganism? Traits must be already present “somewhere” in population for organism to adapt to changing environmental conditions Limited by reproductive potential Only so much DNA Macroevolution Changes that move beyond changes in allele frequency Including origin of new species - speciation, Explains development of new genera and beyond Explains major new features of living organisms Progressive and incremental – example – complex eyes In many cases links between simple and complex are “missing” Are these different species? How about these animals? Defining a Species Population of organisms that can and do: Interbreed Produce fertile offspring Origin of Species The Ultimate of Divergent Evolution Animation Disruptive selection animation. Northern population Arctic Fox Early fox population Spreads northward and southward and separates Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Different environmental conditions lead to different selective pressures and evolution into two different species. Southern population Gray Fox Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat. Reproductive Isolation – Why can’t different species interbreed? Timing - skunks frogs in same pond Behavior birds - songs courtship rituals Other reproductive barriers zygote does not develop - chromosomal differences Live in different geographical areas or in different habitats What comes first?? Geographical isolation always precedes reproductive isolation What is geographical isolation? How can this lead, usually over long time periods, to reproductive isolation? Continual microevolution causes populations to become so different, no longer interbreed Natural selection (in the different environments) Genetic drift and random mutations Tempo of Speciation Darwin’s theory – relatively slow progression to new species as result of geographical isolation Punctuated equilibrium– Long periods, little change, THEN.. rapid changes to new species May be caused by rapid changes in environment Most species last 5 million years before extinction Plate Tectonics Why matching Mesozoic fossils in West Africa and Brazil How does crust movements affect life’s evolution? Pangea – When began to split? LAURASIA 120° 80° 40° 80° 120° 120° 80° 80° 120° GONDWANALAND 135 million years ago 225 million years ago NORTH AMERICA EURASIA AFRICA 120° 80° SOUTH AMERICA INDIA MADAGASCAR 120° 120° 0° AUSTRALIA ANTARCTICA 65 million years ago Figure 5-9 Page 106 Present 40° 120° Mass Extinctions End of Cretaceous – What changes in life forms? What was the cause? What organisms underwent widespread adaptive radiation? End of Permian – 90% of life went extinct Rate of Extinction Biodiversity = speciation minus extinction Background vs mass extinctions As species become extinct, genes “remain” from ancestral species Estimate – human caused extinction increase of 100X to 1000X background READ: The Future of Evolution – answer #1, then #2 (assume you agree) What could be the effect on humans of a mass extinction?
