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Transcript
Evolution. Beginnings: The Big Bang Earth formed more than 4 billion years ago Conditions on Early Earth Organic compounds spontaneously • self-assemble under conditions possible on early Earth Alternatively, compounds might have formed • in deep space and reached earth in meteorites Stanley Miller & Urey experiment How Did Cells Emerge? Self-replicating genetic systems require proteins (including enzymes) and nucleic acids Proteins and nucleic acids may self-assemble • • • Form proto-cells • when certain conditions are met Clay-template hypothesis Hydrothermal vent hypothesis Origins of Self-Replicating Hypothesis: RNA world • • RNA stores genetic information, but breaks apart easily and mutates often Ribozymes: Catalytic RNAs Switch from RNA to DNA • Makes the genome more stable Early Life The First Cells 3.8 billion years ago • • oxygen levels in atmosphere and seas were low early prokaryotic cells probably were anaerobic Divergence • separated bacteria from ancestors of • archaeans and eukaryotes Cyanobacteria evolved • oxygen-releasing, noncyclic pathway Increased oxygen favored aerobic respiration • ATP-forming metabolic pathway • Key innovation in evolution of eukaryotic cells Where did organelles come from? Eukaryotic internal membranes may have evolved through infoldings of cell membrane Endosymbiosis One cell enters and survives inside another Host and guest cells come to depend upon one another for essential metabolic processes Mitochondria and chloroplasts may have evolved by endosymbiosis Early Discoveries 19th century • • advances in geology, biogeography, and comparative morphology awareness of change in lines of descent of species Development of new theories Evolution • Change that occurs • line of descent 19th-century naturalists • • tried to reconcile traditional beliefs with evidence of evolution Lamarck’s theory of inheritance of acquired characteristics • Giraffe’s long neck Voyage of the Beagle Charles Darwin’s observations on a voyage around world led to new ideas about species Descent with Modification Darwin compared • modern armadillo with the extinct glyptodont Variations in Traits Darwin observed • • variations in traits influence an individual’s ability to secure resources – to survive and reproduce Darwin, Wallace, and Natural Selection In 1858, Charles Darwin and Alfred Wallace independently proposed a new theory, that natural selection can bring about evolution What is evolution? Population • • Individuals of the same species in the same area same number and kinds of genes same traits Populations evolve • • Traits that help characterize a population (and a species) can change over generations Gene pool • All the genes of a population Evolution • Change which occurs in a line of descent What is natural selection? Natural selection • • • Differential survival and reproduction among individuals that vary in one or more heritable traits Theory of Natural Selection • • In natural populations • • differential in survival and reproduction among individuals of a population • • • Exhaust resources of its environment lead to increased fitness individual’s adaptation Individuals must compete for resources • food and shelter from predators more competitive tend to produce more offspring natural selection Variation in heritable traits some trait forms are more adaptive than others • bearers more likely to survive and reproduce over generations, adaptive forms of traits tend to become more common in a population • less adaptive forms of same traits become less common or are lost Fossil evidence Fossils • Physical evidence of life in distant past Found in stacked layers of sedimentary rock • • Younger fossils in more recently deposited layers Older fossils underneath, in older layers Geologic time scale Comparative morphology major intervals determined fossil record Correlated with macroevolutionary events Major patterns, trends, rates of change among lineages Includes dates obtained radiometric dating Comparisons body form and structure of major groups of organisms Reveals evolutionary connections • similar body parts that became modified differently in different lineages Evidence of descent from a common ancestor Morphological Convergence Homologous structures: Analogous structures: body parts in different lineages look alike, but evolved separately after • lineages diverged did not evolve in a common ancestor What is mutation ? Life’s diversity arises from mutations • Changes in molecules of DNA which offspring inherit from their parents In natural populations, mutations introduce variation in heritable traits among individuals Variation? Individuals who inherit different combinations of alleles vary in details of one or more traits • Polymorphism: Several alleles in a population Mutations are the original source of new alleles • • Lethal mutations result in death Neutral mutations neither help nor hurt When is A population not evolving? Genetic equilibrium • • A state in which a population is not evolving Never occurs in nature