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Chapter 22 Descent with Modification: A Darwinian View of Life
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evolution** – processes that have transformed life on Earth from its earliest beginnings to its current diversity **greatest underlying principle in biology 1859 Darwin published On the Origin of Species by Means of Natural Selection arguing that species evolved from ancestral forms by natural selection -revolutionized scientific thought, but contrasted sharply with views of the time
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Figure 22.18 Charles Darwin in 1859, the year The Origin of Species was published
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Figure 22.0 Title page from The Origin of Species
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Figure 22.10 Camouflage as an example of evolutionary adaptation
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Linnaeus – (early 1800’s) “father of taxonomy” – branch of biology concerned with naming and classifying diverse forms of life -developed binomial nomenclature – 2 part naming system
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Cuvier – a paleontologist; proponent of catastrophism – Earth’s changes are due to catastrophic events; used fossils to back up his claim Hutton & Lyell – geologists; supported idea of catastrophic events, but changing of Earth gradually Lamarck – believed acquired characteristics could be passed onto organisms (ex: giraffe neck length)
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Darwin’s voyage – 1831 (HMS Beagle) -took him to Galapagos Islands where he developed the idea of adaptation to environment Wallace – 1858 – developed idea of natural selection independently from Darwin & published manuscript (before Darwin, but his was not as thorough)
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Figure 22.5 The Voyage of HMS Beagle
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Darwin’s ideas – descent with modification - unknown ancestral prototype (no idea of genetics) - variation of individuals made differential reproductive success - those best adapted (most fit) leave the most offspring (passing on their characteristics)
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Figure 22.9 A few of the color variations in a population of Asian lady beetles
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Malthus – many organisms reproduce, few offspring survive 1930’s – Population genetics – emphasizes extensive genetic variations within populations & recognizes importance of quantitative inheritance (reconciliation of Mendelism & Darwinism) 1940’s – neoDarwinism – (modern synthesis) – importance of populations, gradualism, & modern genetics
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Natural selection -the idea that organisms with favorable traits are more likely to survive and reproduce
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Evidence for evolution: 1)Biogeography – geographical distribution of a species ex: endemic island species (Australia, Galapagos, Madagascar) 2)Fossil record – supports common descent ex: Archeopteryx links birds, reptiles 3)Taxonomy – reflected branching genealogy
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Figure 22.4 Strata of sedimentary rock at the Grand Canyon
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4) Comparative anatomy – anatomical similarities ex: homologous structures, vestigial organs 5)Comparative embryology – helps identify anatomical homology less apparent in adults; reflects genetic similarity ex: comparing embryos of different vertebrates 6) Molecular biology – similarities in DNA sequences & protein sequences; supports common descent
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Figure 22.14 Homologous structures: anatomical signs of descent with modification
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Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates
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Chapter 23 The Evolution of Populations
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Population -a localized group of individuals belonging to the same species Species -a group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature
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Gene pool – the total aggregate of genes in a population at any one time Hardy-Weinberg theorem - frequencies of alleles and genotypes in a population remain constant over time
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Hardy-Weinberg theorem For a population to be in Hardy-Weinberg equilibrium, these 5 conditions must be met: 1) large population size 2) no migration or emigration 3) no net mutations 4) random mating 5) no natural selection
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Hardy-Weinberg equation p 2 + 2pq +q 2 = 1
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Example 500 plants 480 red (320 RR, 160 Rr) 20 white (rr) diploid = 1000 alleles R = 800 (320 x 2 = 640 RR, 160 x 1 = 160 Rr) = 800/1000 =.8 = 80% r =.2 = 20% R = p, r = q (.8) 2 + 2(.8)(.2) + (.2) 2 = 1.64 +.32 +.04 = 1
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Figure 23.4 Genetic drift
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Figure 23.3b The Hardy-Weinberg theorem
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Figure 23.3a The Hardy-Weinberg theorem
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Microevolution -relative frequencies of alleles in a population change over a succession of generations within a gene pool
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Causes of Microevolution 1)Genetic drift – changes due to chance usu. in small populations -conditions which may reduce population size: a) bottleneck effect – population drastically reduced by disaster, killing unselectively ex: cheetah population – reduced in the ice age, then trophy hunted to near extinction b) founder effect – genetic drift in a new colony for that species ex: colonizing isolated island, lake, etc.
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Figure 23.5 The bottleneck effect: an analogy
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Figure 23.5x Cheetahs, the bottleneck effect
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2)Gene flow – migration of fertile individuals between populations 3)Mutation – changes in DNA 4)Nonrandom mating - may include: selective breeding – choosing mates that are close by (may lead to inbreeding; extreme is self-fertilization) or assortative mating – individuals select partners like themselves in phenotype
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Figure 23.16x1 Sexual selection and the evolution of male appearance
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5)Natural selection – (variation is at the core) polymorphism – when 2 or more distinct forms are present in a population ex: M & F lions (sexual dimorphism); may be balanced (remains set in population)
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Figure 23.16x2 Male peacock
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Figure 23x2 Polymorphism
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geographical variation – genetic differences in population of a species varies regionally ex: cline – graded change along geographic axis recombination & mutation add variety
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Figure 23.8 Clinal variation in a plant
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Variation may be preserved through: diploidy – hides recessive alleles balanced polymorphism – heterozygote advantage ex: sickle cell anemia Aa – resistant to malaria AA – susceptible to malaria aa – sickle cell anemia
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Figure 23.14 Diversifying selection in a finch population
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Figure 23.12x Normal and sickled cells
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Figure 23.10 Mapping malaria and the sickle-cell allele
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Fitness – relative contribution an individual makes to the gene pool of the next generation Relative fitness – contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus
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Modes of Natural Selection 1)Stabilizing selection – favors the mean 2)Directional selection – favors one extreme phenotype over another 3)Diversifying selection – favors both ends of the spectrum, & not the mean **natural selection acts on individuals, but populations evolve
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Figure 23.12 Modes of selection
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