Lecture 19• At the Galapagos island is where Darwin realized that the mocking birds, although similar, seemed to be different species o Some were unique to the individual island o Others lived in two or more adjacent islands o Most Galapagos species resembled those on South American mainland but were not known from anywhere else in the world Hypothesis: Galapagos had been colonized by organisms that strayed from South America and then diversified giving rise to new species on various islands • Adaptations: inherited characteristics of organisms that enhance their survival and reproduction in specific environments • Natural al selection: individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits o Underlying mechanism for decent with modification• Darwin attributed the unity of life to an ancestor of the remote past • Artificial selection: modifying species based on desired traits • Individuals do not evolve, it is the population that evolves over time • Mrcaru lizards have different habitats and diet o Eat much more plant materialo Have larger heads with more powerful jaws o Modified digestive system with cecal valve • Evolution changes the genetic nature of populations o Can lead to the formation of new species Lecture 20• Why is evolution important?o Explanation for the diversity of lifeo Framework for understanding differences and similarities o Helps integrate different areas of biology o Explains otherwise inexplicable aspects of biology • Charles Darwino Began work as a biologist in the 1830’s o There was a widespread belief in a young earth in the European cultureo Evidence from geologists however did not support these ideas o Most compelling evidence Sedimentary geology (where many fossils are formed)• Formation of sedimentary strata with fossilso Rivers carry sediment into aquatic habitats o Sedimentary rock layers (strata) eventually for mover time o Some strata contain fossilso Water levels change and the strata with their fossils get exposed o Darwin engaged on a five year voyage around the world on the Beagle Crucial stop was at the Galapagos Island where Darwin made his ideas about the formation of new species o Evolution: descent with modification – an idea that the earth’s many species are descendants of ancestral species that were different from the present day species • Alfred Russell Wallaceo Spent 14 years in the Amazon and South East Asia o Freelance biologisto Most of his collections from South America were lost in a ship fireo Expert on animal distributionso Had the same ideas as Darwin• Henry Walter Bateso Spent over a decade in the Amazono Freelance biologist• Charles Lyello Leading geologist of Darwin’s time o Uniformitarianism: mechanisms of change are constant over time, the same geological processes are operating today as in the past at the same rate o This idea encouraged Darwin to think that the earth must be much older than everyone thought • Lamarck’s hypothesis of evolutiono Use and disuse: the idea that parts of the body that are used extensively become larger and stronger while those that are not used deteriorate Giraffe stretching his neck for leaves was a cited exampleo Inheritance of acquired characteristics An organism could pass these modifications to its offspring • The long muscular neck of giraffes had evolved over time as giraffes stretched their necks even higher • Darwin’s Five Theorieso Evolution has happened o All life has a common ancestor o The diversity of life is a result of the series of splits in the lineage (family tree) of living thingso Natural selection is the primary mechanism that drives evolutionary change o Evolution occurs gradually over time • Darwin writes “The Origin of Species”• For natural selection to occur in evolution a genetic difference must underlie the phenotypic differenceo Examples is that beetles must pass their color on to their offspring: predator eats the more easily seen beetles that lack the brown gene, thus there is an increase in brown gene frequency • Homology: similarities resulting from common ancestry o Homologous structures: variations on a structural theme that was present in their common ancestor • Vestigial structures: remnants of features that served a function in the organisms ancestors o Example is in some snakes with the vestiges of hip bones and legs from walking ancestors • Evolutionary tree: diagram of evolutionary relationships • Convergent evolution: the independent evolution of similar features in different lineages o Example is the ability to glide through the air of the North American flying squirrel and the Australian Sugar Glider o Features are said to be analogous not homologous Features share similar function but not common ancestry Homologous share common ancestry but not necessarily similar functionLecture 21• Fossils: remains or traces of organisms from the past o Georges Cuvier noticed that the older the stratum the more dissimilar its fossils were to current life form o From one layer to the next, new species appeared while others disappeared o Therefore extinctions must have been a common occurrence • Darwin’s 5 theories o Evolution has happened Not new to Darwin in any way o All life has a common ancestor Darwin had little evidence of this strongly supported by molecular and cellular datao The diversity of life is a result of the series of splits in the family tree of living things Generally true although other patterns occur o Natural selection is the primary mechanism driving evolutionary change Multiple evolutionary forces o Evolution occurs gradually over time Disputed among biologists but evolution can happen rapidly as it did with the lizards• Darwin’s evidence o Fossil record Nonrandom change in form over time Not just different in the past but different in a consistent patterno Homology (comparative morphology) Different species have the same structure modified in different ways Homology: similarity resulting from a common ancestor Example: the similarity of the structure in the forelimbs of humans, cats, whales and bats • Similar structure but with different functions (lifting, walking, swimming and flying)• Homologous structures: represent variations on a structural theme that was present in a common ancestor Similarity during
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