Chapter 13: How Populations Evolve Evidence for Evolution II. Artificial Selection III. Fossil Record IV. Comparative Anatomy V. Comparative embryology VI. Genetic Analysis VII. Biogeographical Evidence VIII. Conclusions Evolution = descent with modification Macroevolution = large changes Microevolution = small changes Both rely on same mechanisms Primarily natural selection Charles Darwin: On the Origin of Species (mid-18 s) Nothing in biology makes sense except in the light of evolution --Theodosius Dobzhansky Traveled extensively Galapagos Islands off the coast of Ecuador One area of focus: finches The Galápagos Islands Pinta Genovesa Marchena Equator Santiago Daphne Pinzón Islands Fernandina Isabela Santa Cruz Santa San Fe Cristobal 4 km Florenza Española 4 miles North America ATLANTIC South America Andes Tierra del Fuego Great Britain Cape Horn Cape of Good Hope Europe Africa Asia Equator Australia Tasmania New Zealand While on the voyage of the HMS Beagle in the 183s Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands Finches of the Galapagos 13 species Difference between them: Beak shape Seed crackers Cactus eaters Tool users Vampire Darwin s idea: One original species has adapted to different food sources Darwin proposed natural selection as the mechanism of evolution Darwin observed that organisms Produce more offspring than the environment can support Vary in many characteristics that can be inherited Darwin reasoned that natural selection 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 The selective breeding of domesticated plants and animals Charles Darwin, 1859: On the Origin of the Species Charles Darwin proposed Natural Selection as the mechanism of evolution 1
II. Artificial Selection CAN selection produce major evolutionary change? 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 Broccoli, brussel sprouts, kale, cabbage, & cauliflower II. Artificial Selection (cont.) B) Mammals: Dogs Change can happened over a very short geological period if the selection pressure is strong! All artificially selected from Brassica oleracea Fossils: Preserved remains of ancient organisms How to make a fossil: Burial in sediment Mineralization of organic material Hardening of sediment Darwin and his contemporaries saw and knew of fossils: Local fossils looked like local organisms Progressive changes in layers Organization of fossils: a) Fossils are found in distinct 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 b) Resemblance to modern forms of life gradually increases with younger fossils Ancient primitive organisms Several intermediary stages Modern forms c) Many fossils are of species now extinct Conclusions: Many different types of organisms in the past (some extinct) Change in lineages over time Fossil Record of Evolution: Whale Evolution Rodhocetus kasrani reduced hind limbs could not walk; swam with up-down motion like modern whales Pakicetus attocki lived on land; skull had whale characteristics Modern toothed whales Ambulocetus natans walked on land like sea lions swam by flexing & paddling like otters Copyright 25 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 Fish, amphibians, reptiles, mammals, and birds appear in order Seedless vascular plants, seeds, gymnosperms, and angiosperms appear in order : Evidence for Mass Extinctions Number of families Diversity over the Last 6 Million Years 8 6 4 2 6 5 4 3 2 1 Cambrian Silurian Carboniferous Triassic Cretaceous (545-49) (438-48) (36-28) (248-213) (144-65) Ordovician (49-438) Devonian (48-36) Permian (28-248) Millions of years ago Jurassic (213-144) Tertiary (65-2) IV. Comparative Anatomy Similar anatomy is found in organisms with greatly divergent functions Homologous structures 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 No apparent purpose Resemble similar functional structures in other, closely related species also human appendix Evolution helps us understand patterns in the diversity of life 3
V. Comparative Embryology Embryological stages all vertebrate embryos look similar early in their development evidence of common ancestry similar developmental instructions in DNA V. Embryology and Comparative Development pig cow rabbit human Comparative Development Reveals Descent from a Common Ancestor VI. Genetic Analysis Modern technology reveals relatedness among diverse organisms 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) Molecular Record Independent test Distantly related organisms are expected to accumulate a greater number of evolutionary differences than closely related species. VII. Biogeographical Evidence 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 VIII. Conclusions There are many documented cases of Evolution in Action Darwin s Finches beak size Grant and Grant 197s 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 " 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 End Evolution 5