Beginnings: The Big Bang Earth formed more than 4 billion years ago Nanobes Life in Thermal Pools.
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Transcript of Beginnings: The Big Bang Earth formed more than 4 billion years ago Nanobes Life in Thermal Pools.
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Beginnings: The Big Bang
Earth formed more than 4 billion years ago
Nanobes
Life in Thermal Pools
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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
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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
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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
Early Life
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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
Stromatolites
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Where did organelles come from?
Eukaryotic internal membranes may have evolved through infoldings of cell membrane
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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
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Early Discoveries 19th century
• advances in geology, biogeography, and comparative morphology
• awareness of change in lines of descent of species
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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
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Voyage of the Beagle Charles Darwin’s observations on a
voyage around world led to new ideas about species
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Descent with Modification
Darwin compared •modern armadillo with the extinct
glyptodont
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Variations in Traits Darwin observed •variations in traits influence an
individual’s ability to secure resources – to survive and reproduce
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Darwin, Wallace, and Natural Selection
In 1858, Charles Darwin and Alfred Wallace independently proposed a new theory, that natural selection can bring about evolution
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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
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What is natural selection?
Natural selection• In natural populations• Differential survival and reproduction among
individuals that vary in one or more heritable traits
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Theory of Natural Selection•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
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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
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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
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Geologic time scale major intervals
determined fossil record
Correlated with macroevolutionary
events Major patterns,
trends, rates of change
among lineages Includes dates obtained radiometric dating
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Comparative morphology Comparisons body form
and structure of major groups of organisms
Reveals evolutionary connections
Homologous structures: • similar body parts
that became modified differently in different lineages
Evidence of descent from a common ancestor
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Morphological Convergence
Analogous structures: body parts in different lineages
look alike, but evolved separately after • lineages
diverged did not evolve in a
common ancestor
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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
Super rats
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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
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When is A population not evolving?
Genetic equilibrium•A state in which a population is not
evolving•Never occurs in nature