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Evolutionary Theory Theory = set of well-supported, interrelated hypotheses, explaining a number of related natural phenomena e.g. – Gravitational theory – Cell theory – Evolutionary theory Evolution not a new idea in Darwin’s age • Related indigenous concepts: – transformation: animal human – close kinship between animals, plants and humans – awareness of different “ages” or “worlds” and “progression” throughout time in various cultures • Anaximander ~ 550 B.C. (Greek philosopher): “humans descend from fishes” • Erasmus Darwin, J-B Lamarck a.o. 18th century (British naturalists): “life evolves as environments change” 1 • Charles Darwin 1859: On the Origin of Species by Means of Natural Selection (also: Alfred Wallace) – Descend with modification (=evolution) – New: Natural selection (=mechanism for evolution) • C. Darwin’s ideas influenced by his experience and observations… England EUROPE NORTH AMERICA ATLANTIC OCEAN PACIFIC OCEAN Galápagos Islands HMS Beagle in port SOUTH AMERICA AUSTRALIA Andes Darwin in 1840, after his return AFRICA Cape of Good Hope Tasmania Cape Horn New Zealand Tierra del Fuego 2 …as well as by ideas of other scientists Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Mendel (inheritance) American Revolution French Revolution Wallace (evolution, natural selection) U.S. Civil War 1800 1750 1795 1850 Hutton proposes his theory of gradualism. 1900 1798 Malthus publishes “Essay on the Principle of Population.” 1809 S&T Lamarck publishes his theory of evolution. Lyell publishes Principles of Geology. 1830 Darwin travels around the world on HMS Beagle. 1831–1836 1837 Darwin begins his notebooks on the origin of species. 1844 Darwin writes his essay on the origin of species. 1858 Wallace sends his theory to Darwin. The Origin of Species is published. 1859 1865 Mendel publishes inheritance papers. The historical context of Darwin’s life and ideas Logic of Evolutionary Theory: • • • • Observation 1: individual variation (heritable) Observation 2: over-reproduction & competition Inference 1: unequal reproductive success Inference 2: favored traits increase in population 3 (a) Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. (c) Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. (b) Insect eater. The green warbler finch (Certhidea olivacea) uses its narrow, pointed beak to grasp insects. Beak variation in Galápagos finches (a) A flower mantid in Malaysia (b) A stick mantid in Africa Camouflage as an example of evolutionary adaptation 4 Evidence of Evolution 1. Natural Selection “in action” 2. Homologies: structures of common origin (anatomical & molecular) indicative of divergent evolution 3. Biogeography: geographic distribution of species 4. Fossil Record 1. Natural Selection “in action” a. Differential predation on guppy populations: EXPERIMENT John Endler transplanted guppies from pools with pike-cichlids (active guppy predators) to pools with killifish (less active predators), and measured number and area of brightcolored spots on male guppies over 15 generations (22 months). Pools with killifish, but not guppies prior to transplant Experimental transplant of guppies Predator: Killifish; preys mainly on small, juvenile guppies which do not express color gene Guppies: Adult males have brighter colors Predator: Pike-cichlid; preys mainly on larger, adult guppies Guppies: Adult males are more drab in color 5 b. Evolution of drug-resistant microbes: e.g. HIV Patient No. 1 Patient No. 2 Patient No. 3 Weeks 6 e.g. Staphylococcus aureus c. “Artificial” Selection (breeding) Terminal bud Cabbage Lateral buds Brussels sprouts Flower cluster Leaves Cauliflower Kale Stem Flower and stems Broccoli Wild mustard Kohlrabi 7 Humans select desirable traits in crops, farm animals, pets (e.g. dogs)… resulting in very different new forms over time, e.g. Hopi people breeding different strains of corn adapted to different environments d. Response to change in food source 8 2. Homologies • Anatomical Homologies: a. Adult homologous structures, e.g. fore limbs Human Cat Whale Bat b. Vestigial structures = remnants of structures that served important functions in the organism’s ancestors e.g. vestiges of pelvis & leg bones in some snakes and whales 9 c. Embryonic homologous structures Pharyngeal pouches Post-anal tail Chick embryo Human embryo Figure 22.15 Anatomical similarities in vertebrate embryos • Molecular Homologies: d. DNA & universal genetic code Second mRNA base C UUU UUC U UUA First mRNA base (5′ end) UUG C Phe Leu UCC UCA UAC Ser CCU CAU CAC AUC Leu CCA Pro CAA CCG lle CAG ACU AAU ACC AAC AUA ACA AUGMet or start ACG Thr AAA AAG GUU GCU GAU GUC GCC GAC GUA GUG Val GCA GCG Tyr UGC U Cys C S&T UAG Stop UGG Trp G UCG CCC CUA G UGU UAA Stop UGA Stop A CUU AUU G UAU CUC CUG A A UCU Ala GAA GAG His Gln Asn Lys U CGU CGC CGA Arg Glu A CGG G AGU U Ser C AGC A AGG Arg G AGA U GGU Asp C GGC GGA GGG Gly Third mRNA base (3′ end) U Figure 17.5 The dictionary of the genetic code C A G 10 e. Gene products (proteins), e.g. hemoglobin Species Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide 100% Human Rhesus monkey 95% Mouse 8 7% Chicken 69% Frog Lamprey 54% 14% Figure 22.16 Comparison of a protein found in diverse vertebrates 3. Biogeography • Closely related species found in same geographic region • Islands have many endemic species • Analagous structures may evolve in different geographic areas - indicative of convergent evolution 11 NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel 4. Fossil Record • (Incomplete) Succession of life forms from oldest (in deeper strata) to youngest (in shallower strata) 12 Some fossils represent evolutionary “dead-ends” while others represent ancestral forms = transitional species • Cetaceans evolved from terrestrial mammals 13