Download Evolution

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Evolution.
Beginnings: The Big Bang
Earth formed more than 4 billion years ago
Conditions on Early Earth
Organic compounds spontaneously
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self-assemble under conditions possible on early Earth
Alternatively, compounds might have formed
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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
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Form proto-cells
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when certain conditions are met
Clay-template hypothesis
Hydrothermal vent hypothesis
Origins of Self-Replicating
Hypothesis: RNA world
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RNA stores genetic information, but breaks apart easily and mutates often
Ribozymes: Catalytic RNAs
Switch from RNA to DNA
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Makes the genome more stable Early Life
The First Cells
3.8 billion years ago
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oxygen levels in atmosphere and seas were low
early prokaryotic cells probably were anaerobic
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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
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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
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advances in geology, biogeography, and comparative morphology
awareness of change in lines of descent of species
Development of new theories
Evolution
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Change that occurs
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line of descent
19th-century naturalists
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tried to reconcile traditional beliefs with evidence of evolution
Lamarck’s theory of inheritance of acquired characteristics
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Giraffe’s long neck
Voyage of the Beagle
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Charles Darwin’s observations on a voyage around world led to new ideas about
species
Descent with Modification
Darwin compared
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modern armadillo with the extinct glyptodont
Variations in Traits
Darwin observed
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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
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Individuals of the same species in the same area
same number and kinds of genes same traits
Populations evolve
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Traits that help characterize a population (and a species) can change over
generations
Gene pool
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All the genes of a population
Evolution
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Change which occurs in a line of descent
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What is natural selection?
Natural selection
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Differential survival and reproduction among individuals that vary in one or
more heritable traits
Theory of Natural Selection
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In natural populations
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differential in survival and reproduction among individuals of a population
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Exhaust resources of its environment
lead to increased fitness
individual’s adaptation
Individuals must compete for resources
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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
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bearers more likely to survive and reproduce
over generations, adaptive forms of traits tend to become more common in a
population
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less adaptive forms of same traits become less common or are lost
Fossil evidence
Fossils
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Physical evidence of life in distant past
Found in stacked layers of sedimentary rock
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Younger fossils in more recently deposited layers
Older fossils underneath, in older layers
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Geologic time scale
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Comparative morphology
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 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
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similar body parts that became modified differently in different lineages
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Evidence of descent from a common ancestor
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Morphological Convergence
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Homologous structures:
Analogous structures: body parts in different lineages
look alike, but evolved separately after
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lineages diverged
did not evolve in a common ancestor
What is mutation ?
Life’s diversity arises from mutations
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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
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Polymorphism: Several alleles in a population
Mutations are the original source of new alleles
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Lethal mutations result in death
Neutral mutations neither help nor hurt
When is A population not evolving? Genetic equilibrium
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A state in which a population is not evolving
Never occurs in nature