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Organic Evolution &
Natural Selection
Evolution
► development
of complex life forms
 through mutation and selection
 natural selection - survival of the
►fittest
(for a niche)
►luckiest
►combination
Evolution
► species
 reproductively isolated group of living
organisms
► population
 group of organisms consisting of all the
members of a species living in an area
Evolutionary Trends
► speciation
& extinction
► divergence & convergence
► phyletic gradualism & punctuated
equilibrium
Organic evolution:
observations
► sedimentary
rocks
 deposited in layers
 oldest layers are on the bottom
 layers may be correlated with other sedimentary
layers
► fossil
record
 oldest rocks have only simple fossils
 younger rocks have more organisms similar to
those living today (at levels from species to
kingdom)
 fossils record includes appearances and
extinctions of many species
Organic evolution:
observations
► geographic
distribution of organisms
 many organisms are similar but unique
 they are confined to specific areas (islands,
continents, water bodies)
 includes modern and fossil organisms
 distribution has changed through time
Organic evolution:
observations
► anatomy
 cell structure is similar in all living
organisms
 embryology - embryos of mammals, birds,
and reptiles are very similar
 homologus organs - similar organs,
different functions
 vestigal organs - no purpose in one,
purpose in another
Organic evolution:
observations
► genetics
 structure of DNA and RNA is the same in
all living organisms
 similarity in genetic code varies between
organisms (some organisms are more
similar than others)
Organic evolution:
conclusions
► the
characteristics of populations of
living organisms have changed
through time
 life has become more complex
 life has become more diverse
 this is excepted as a factual observation
► all
life is related
Organic evolution: observations
► What
about “missing links”
 the “link” between two fossil species OR
between a fossil species and a living
species
 many found, yet none found
 each “gap” filled creates two new “gaps”
Natural selection:
observations
► populations
of organisms display a variety of
characteristics
 characteristics may be useful, not useful, or
detrimental
 the variety is reflected in an organisms genes
► new
genes
 provide variety
 produced by mutation, duplication, or exchange
of genes
 passed to offspring during reproduction
Natural selection:
observations
► artificial
selection
 domesticated plants and animals can be
bred to favor certain characteristics
 populations of wild and domestic plants
and animals develop characteristics that
favor their survival
Natural selection:
observations
► the
natural environment
 provides opportunities and stresses for
living organisms
 a new niche or stress on an existing niche
will enhance selection
Natural selection: observations
► populations
isolated
of a species may become
 by geography or behavior
 provides new opportunities and stresses
 isolates the population from the larger
gene pool
Natural selection: conclusion
►
►
►
the natural environment provides conditions
(opportunities and stresses) that result in evolution
through the process of natural selection
organisms with favorable characteristics for their
niche are more likely to thrive and reproduce while
organisms with unfavorable characteristics are less
likely to thrive and reproduce
over time, favorable characteristics can accumulate
in a population until the members of the population
can no longer reproduce with the population from
which they became isolated
Evolutionary trends
► speciation
& extinction
► divergent & convergent evolution
► phyletic gradualism & punctuated
equilibrium
Natural selection: speciation
►a
population has a gene pool
► members of the population interbreed
► the population may become isolated from
others of a species
 development of niches & resource partitioning
 migration
 development of physical barriers
► populations
may be selected
 by stress
 by opportunity
► isolation
may result in genetic divergence
Natural selection: extinction
► stress
on limiting factors reduce or
destroy a population
► evolution into subsequent species
(pseudo-extinction)
Phylogeny
► relationships
between organisms can
be determined using
 genetics
 anatomy & physiology
 Fossils
Phyletic Gradualism &
Punctuated Equilibrium
► gradualism
 slow, steady change
► equilibrium
& punctuation
 long periods with little change
 short bursts of rapid change
How did it start?
► Chemical
evolution?
► Where?




deep ocean vents?
tidal pools?
ice surface?
clay surface?
Randomness
► evolution
is not random
► natural selection is not random
► mutations are random
► favorable mutations survive through
reproduction
End point
► Evolution
has no end