Transcript Evolution

Beginnings: The Big Bang
 Earth formed more than 4 billion years ago
Life in Thermal Pools
Nanobes
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
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
Stromatolites
• 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
• In natural populations
• Differential survival and reproduction among individuals that
vary in one or more heritable traits
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
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
 major intervals determined
 fossil record
 Correlated with
 macroevolutionary events
 Major patterns, trends,
 rates of change among
lineages
 Includes dates obtained
 radiometric dating
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
Morphological Convergence
 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
Super rats
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