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Biogeography • Size of the known world expanded enormously in 15th century • Accepted beliefs did not explain discovery of new organisms in previously unknown places Biogeography Comparative Morphology • Study of similarities and differences in body plans of major groups • Puzzling patterns: – Animals as different as whales and bats have similar bones in forelimbs – Some parts seem to have no function Comparative Morphology coccyx fossilized ankle bone ankle bone Geological Discoveries • Similar rock layers throughout world • Certain layers contain fossils • Deeper layers contain simpler fossils than shallow layers • Some fossils resemble known species 19th Century: New Theories • Scientists attempt to reconcile evidence of change with traditional belief in a single-creation event • Two examples – Georges Cuvier: multiple catastrophes – Jean Lamarck: inheritance of acquired characteristics The Theory of Uniformity • Lyell’s Principles of Geology • Earth shaped by subtle, repetitive processes of change • Challenged the view that Earth was only 6,000 years old Darwin’s Voyage • At age 22, Charles Darwin began a fiveyear, round-the-world voyage aboard the HMS Beagle • As ship’s naturalist, he collected and examined species that inhabited regions the ship visited Darwin’s Voyage Fossil Evidence • Darwin found fossil Glyptodont • Proposed descent with modification Voyage of the Beagle EQUATOR Galapagos Islands Galapagos Islands Darwin Wolf • Volcanic islands far off coast of Ecuador Pinta Genovesa Marchena • All inhabitants are descended from species that arrived on islands from elsewhere Santiago Bartolomé Fernandia Seymour Baltra Rabida Pinzon Santa Cruz Santa Fe Tortuga San Cristobal Isabela Española Floreana Malthus: Struggle to Survive • Thomas Malthus, a clergyman and economist, wrote essay that Darwin read on his return to England • Argued that as population size increases, resources dwindle, the struggle to live intensifies, and conflict increases Galapagos Finches • Darwin observed finches with a variety of lifestyles and body forms • On his return, he learned that there were 13 species • He attempted to correlate variations in their traits with environmental challenges Galapagos Finches Reproductive Capacity and Competition • All populations have the capacity to increase in numbers • No population can increase indefinitely • Eventually, individuals of a population end up competing for resources Variation in Populations • All individuals have the same genes that specify the same assortment of traits • Most genes occur in different forms (alleles), which produce different phenotypes • Some phenotypes compete better than others (fitness) Change over Time • Over time, alleles that produce the most successful phenotypes will increase in the population • Less successful alleles will become less common • Change leads to increased fitness – Increased adaptation to environment Natural Selection • Natural selection for various traits among individuals of a population affects which individuals survive and reproduce in each generation • Process results in adaptation to the environment (increases fitness) Alfred Wallace • Naturalist who arrived at the same conclusions Darwin did • Wrote to Darwin describing his views • Prompted Darwin to finally present his ideas in a formal paper Adaptation • Some heritable aspect of form, function, or behavior that improves the odds for surviving and reproducing • Environment specific • Outcome of natural selection Adaptation to What? • Llamas live at high altitude and have hemoglobin with a high oxygen affinity • Is this an adaptation to altitude? Probably not • Llamas are related to camels, which live at low altitudes • Camels also have hemoglobin with high oxygen-binding capacity Common Ancestors • Llama and camel Populations Evolve • Biological evolution changes populations, not individuals • Traits in a population vary among individuals • Evolution: change in the frequency of traits The Gene Pool • All the genes in a population • Genetic resource that is shared (in theory) by all members of population Variation in Phenotype • Each gene in gene pool may have two or more alleles • Individuals inherit different allele combinations – leading to variation in phenotype • Offspring inherit genes, not phenotypes What Determines Alleles in a New Individual? • Mutation • Crossing over at meiosis I • Independent assortment • Fertilization • Change in chromosome number or structure Reproductive Isolation • Cornerstone of the biological species concept • Speciation is the attainment of reproductive isolation • Reproductive isolation arises as a by-product of genetic change Biological Species Concept • “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.”