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Chapter 13: How Populations Evolve Evidence for Evolution I. Evolution & Darwin II. Artificial Selection III. Fossil Record IV. Comparative Anatomy V. Comparative embryology VI. Genetic Analysis VII. Biogeographical Evidence VIII. Conclusions I. Evolution & Darwin Evolution = descent with modification Æ Macroevolution = large changes Æ Microevolution = small changes Both rely on same mechanismsÆ Primarily natural selection Charles Darwin: On the Origin of Species (mid-1800’s) “Nothing in biology makes sense except in the light of evolution” --Theodosius Dobzhansky I. Evolution & Darwin I. Evolution & Darwin • Traveled extensively • Galapagos Islands—off the coast of Ecuador • One area of focus: finches North America Great Britain Europe • Finches of the Galapagos • 13 species • Difference between them: Asia – Beak shape ATLANTIC OCEAN PACIFIC OCEAN Africa PACIFIC OCEAN Equator The Galápagos Islands Pinta PACIFIC OCEAN South America Genovesa Fernandina 0 0 Isabela Santa Santa San Cruz Fe Cristobal 40 km Florenza Española 40 miles Seed crackers Cactus eaters “Tool users” Vampire Australia Andes Marchena Equator Santiago Daphne Pinzón Islands • • • • Cape of Good Hope Cape Horn Tasmania New Zealand Tierra del Fuego While on the voyage of the HMS Beagle in the 1830s Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands I. Evolution & Darwin Darwin proposed natural selection as the mechanism of evolution – Darwin observed that organisms z Produce more offspring than the environment can support z Vary in many characteristics that can be inherited – Darwin reasoned that natural selection z Results in favored traits being represented more and more and unfavored ones less and less in ensuing generations of organisms – Darwin found convincing evidence for his ideas in the results of artificial selection z The selective breeding of domesticated plants and animals • Darwin’s idea: – One original species has adapted to different food sources Charles Darwin, 1859: On the Origin of the Species Charles Darwin proposed Natural Selection as the mechanism of evolution 1 II. Artificial Selection II. Artificial Selection (cont.) CAN selection produce major evolutionary change? Æ Darwin found convincing evidence for his ideas in the results of artificial selection Artificial selection: • organisms may be modified by controlled breeding • and change drastically in short time periods! • 2 examples… A) Plants B) Mammals: Dogs Change can happened over a very short geological period if the selection pressure is strong! ÆBroccoli, brussel sprouts, kale, cabbage, & cauliflower Æ All artificially selected from Brassica oleracea III. The Fossil Record Fossils: Preserved remains of ancient organisms III. The Fossil Record III. The Fossil Record How to make a fossil: Æ Burial in sediment Æ Mineralization of organic material Æ Hardening of sediment Organization of fossils: a) Fossils are found in distinct layers Darwin and his contemporaries saw and knew of fossils: Æ Local fossils looked like local organisms Æ Progressive changes in layers • Fossil Record – Remains or evidence of past life – Dating fossils • Relative dating – old layers under new • Absolute dating – radioactive decay – Fossilization chancy • Right kind of organism, in right place • Gaps unavoidable – Many excellent series though • Horses, titanotheres, whales, humans 2 Organization of fossils: a) Fossils are found in distinct layers Fossil Record of Evolution: Whale Evolution b) Resemblance to modern forms of life gradually increases with younger fossils Modern toothed whales Ancient primitive organisms Æ Several intermediary stages Æ Modern forms Rodhocetus kasrani reduced hind limbs could not walk; swam with up-down motion like modern whales c) Many fossils are of species now extinct Ambulocetus natans walked on land …like sea lions Pakicetus attocki lived on land; skull had whale characteristics Conclusions: Æ Many different types of organisms in the past (some extinct) Æ Change in lineages over time swam by flexing & paddling … like otters Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Facts – Geology and Fossils • Fossils are found in sedimentary rocks • Many fossils represent extinct organisms • Oldest sedimentary rocks contain no fossils, or fossils of extremely simple organisms – Prokaryotes (stromatolites) • Fossil prokaryotes appear prior to fossil eukaryotes • Colonial eukaryotes appear prior to multicellular eukaryotes (invertebrates and plants) • Invertebrates appear prior to vertebrates III. The Fossil Record: Evidence for Mass Extinctions Diversity over the Last 600 Million Years Number of families III. The Fossil Record 800 600 400 200 0 600 500 Cambrian (545-490) 400 Silurian (438-408) Ordovician (490-438) 300 200 0 100 Carboniferous Triassic Cretaceous (360-280) (248-213) (144-65) Devonian (408-360) Permian Jurassic (280-248) (213-144) Tertiary (65-2) Millions of years ago –Fish, amphibians, reptiles, mammals, and birds appear in order • Seedless vascular plants, seeds, gymnosperms, and angiosperms appear in order IV. Comparative Anatomy Similar anatomy is found in organisms with greatly divergent functions Homologous structures Æ structures that may have different appearances and functions, yet all derived from a common ancestor Vestigial structures are Evolutionary relicts. They present a strong argument for common ancestry. Vestigial structures Æ No apparent purpose Æ Resemble similar functional structures in other, closely related species Æ also human appendix Evolution helps us understand patterns in the diversity of life 3 V. Comparative Embryology Embryological stages V. Embryology and Comparative Development pig cow rabbit human Æ all vertebrate embryos look similar early in their development Comparative Development Reveals Descent from a Common Ancestor Æ evidence of common ancestry Æ similar developmental “instructions” in DNA VI. Genetic Analysis Modern technology reveals relatedness among diverse organisms Molecular Record – Independent test Æ Distantly related organisms are expected to accumulate a greater number of evolutionary differences than closely related species. • Essentially all organisms have DNA as genetic material • With very few exceptions, all organisms use the same genetic code • Similarities in genes and proteins exist in predictable ways (based on morphological similarities) VII. Biogeographical Evidence VIII. Conclusions • Islands often have unique (endemic) species • Species on islands are most similar to those on nearest continent (or nearest island) Species of Gallotia lizards on the Canary Islands There are many documented cases of Evolution in Action • Darwin’s Finches – beak size – Grant and Grant – 1970s • Showed beak size heritable and responsive to environmental change • Pesticide and Antibiotic resistance 4 VIII. Conclusions: Evolution in Action Insects: Pesticide resistance (Florida) Agent of Natural Selection: Pesticide called "Combat®" End Evolution – Cockroaches who like bait: continuously killed – Those who didn’t like bait: survived • Had rare, glucose disliking mutation – Bait now is ineffective>> populations are resistant 5