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Evolution by Means of NATURAL SELECTION Chapter 22 In the 1830’s, what was known about… • Geology? – The Earth is very old – Slow change can build and result in profound geologic changes over time – Darwin brought work by Lyell (1830) with him on his voyage In the 1830’s, what was known about… • Classification? – Carolus Linnaeus (1707-1778) – founder of taxonomy and binomial nomenclature – Clustered similar organisms into categories, he did not assume any evolutionary relationship based on this classification scheme In the 1830’s, what was known about… • Paleontology? – developed by Cuvier (1769-1832) – He noticed that species appear and disappear in the fossil record In the 1830’s, what was known about… • Heredity? – Mendel didn’t publish his work until 1865, and it wasn’t recognized until the early 1900’s In the 1830’s, what was known about… • Molecular genetics? – 100 years before Griffith’s pneumococcus transforming factor experiment Relating environmental change to biological evolution: • Theories of biological evolution begin in the late eighteenth century • Jean Baptiste Lamarck was the first to propose a mechanism that related environment to biological changes (1809) – Use and Disuse – Inheritance of Acquired Characteristics Darwin • Sails on Beagle at 22 • Noted that organisms of islands off of SA were more like continental species than those of other islands with similar climate and habitats • Contributions of Lyell and others along with his observations lead him to his mechanism for evolution LE 22-6 Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects. Evolution • What is evolution? • Change in the gene pool of a population over generations (often in response to environmental changes) • All of the accumulated changes that have occurred over time • Darwin’s definition: Descent with modification • Life’s history is a tree with different branches • Darwin used Linnaeus’ taxonomic classification scheme to connect diversity of life • Domain > Kingdom > phylum > class > order > family > genus > species Mechanism : Natural Selection • Fact 1: Over-reproduction occurs in nature • Fact 2: Populations do not increase exponentially • Fact 3: There are limited natural resources (food, shelter) • Inference 1: • struggle for survival ensues • Fact 4: Variation exists in populations • Fact 5: Much of the variation is heritable • Fact 4 was physically observed. Darwin’s weakness (at that time) was the 5th fact • Inference 2: • Organisms with the best variations survive the struggle for life • Inference 3: • Unequal survival of organisms with different variations leads to favorable variations accumulating over time Key Concepts • What is the raw material necessary for the mechanism of Natural Selection? • Heritable variations !!! • What is the smallest unit of evolution? • Populations !!! Examples of Natural Selection • Grants on the island of Daphne Major – observed shifts in the frequency of beak sizes over short periods of time • Antibiotic resistance in bacteria • Pesticide/herbicide resistance • How do genetic variations arise in nature? What is wrong with this idea? Evidence for Evolution • Artificial selection • Island biogeography: closely related species tend to be found in the same geographical region, species found at a distance tend to be less related even if they occupy similar niches • Fossil record • Comparative Anatomy • Vestigial Structures • Comparative Embryology/Evo Devo biology • Molecular Biology – all organisms have DNA, common genetic code, ATP, other enzymes LE 22-15 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo Eye sockets in blind salamanders LE 22-16 Species Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Human 100% Rhesus monkey 95% 87% Mouse 69% Chicken 54% Frog Lamprey 14% 200 160 120 80 40 185.6 161.5 67.5 76.1 Males Females Age of guppies at maturity (days) Mass of guppies at maturity (mg) LE 22-12b 100 80 60 40 20 85.792.3 58.2 48.5 Males Females Control population: Guppies from pools with pike-cichlids as predators Experimental population: Guppies transplanted to pools with killifish as predators LE 22-17 NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel •Forks of the tree represent common ancestors •Most closely related organisms share common paths on the branching tree