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 material o 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 life o Framework for understanding differences and similarities o Helps integrate different areas of biology o Explains otherwise inexplicable aspects of biology Charles Darwin o Began work as a biologist in the 1830 s o There was a widespread belief in a young earth in the European culture o 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 fossils o Rivers carry sediment into aquatic habitats o Sedimentary rock layers strata eventually for mover time o Some strata contain fossils o 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 Wallace o Spent 14 years in the Amazon and South East Asia o Freelance biologist o Most of his collections from South America were lost in a ship fire o Expert on animal distributions o Had the same ideas as Darwin Henry Walter Bates o Spent over a decade in the Amazon o Freelance biologist Charles Lyell o 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 evolution o 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 example o 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 Theories o 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 things o 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 difference o 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 ancestors o Example is in some snakes with the vestiges of hip bones and legs from walking 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 function Lecture 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 data o 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 pattern o 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 development can be explained via common ancestors o Island species Similar to mainland but unique Endemic species found nowhere else in the world Inferred that individuals arrived on the islands followed by evolution of
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