Transcript Evolution - GEOCITIES.ws

Charles Darwin
• Born 1809 in England
• Naturalist of the
H.M.S. Beagle
• Through his travels
he made numerous
observations that led
him to propose a
theory of how life
changes over time.
Darwin’s Voyage
Darwin’s Observations & Influences
• Patterns of Diversity
seemed to rely on the
environment.
• Darwin collected
numerous fossils,
some of which were
of species no longer
seen.
• Geologist James
Hutton: geological
changes of Earth
• Charles Lyell:
Geology suggests the
earth is extremely old.
• Jean Lamarck:
selective use of
organs led to certain
traits and these traits
were passed on to
offspring.
Darwin’s Finches
Artificial Selection
• Humans select the genetic variations that
are desired and breed organisms with that
trait in order to produce offspring with the
desired trait.
• Examples: Horse breeding for speed
Agricultural scientists using plants to develop
new vegetables
Meat producers breeding for lean meat
Evolution by Natural Selection
• Darwin was convinced that artificial
selection works in nature.
– Competition for resources
– Predators that are faster or better equipped
will win in competition.
– Survival of the Fittest: Those best adapted to
their environment will survive, reproduce and
pass on their traits to their offspring.
– Over time, natural selection will result in a
population of organisms that have traits that
make them better suited for survival.
Natural Selection
• Cannot be seen in one individual.
• Can only be observed as changes
in a population over many
generations.
Evidence of Evolution
(Change over Time)
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The Fossil Record
Homologous body structures
Similarities in Embryology
DNA analysis
Fossils
• Remains of ancient life,
formed at different times
during Earth’s history.
• Fossils document that life
on Earth has changed
over time.
• 99 % of all species that
have ever lived on Earth
have become extinct
(they no longer exist).
• Imprints of dead
organisms in rock.
How are Fossil dated?
• Relative dating – the
age of the fossil is
determined by
comparing its
placement with the
placement of fossils in
other layers of rock.
The lower layers are
older than the upper
layers.
• All living things are mostly made of carbon.
• A small portion of this carbon is in the form of Carbon14, an unstable radioactive isotope.
• Once an organism dies, the C-14 in the organism
begins to disintegrate. Because it disintegrates at a
steady, known rate, scientists can measure the
amount of C-14 remaining and use a scientific formula
to determine the age of the sample.
• Half-life: the length of time for half of the radioactive
atoms in a sample to decay. C-14 has a high life of
5730 years. For rocks older than 60,000 years,
potassium-40 is used. It has a half life of 1.26 billion
years.
Homologous structures
Structures that are constructed from the same bones, yet have different functions.
Homologous vs. Analagous
Structures
Embryonic Development
Comparisons
The same groups of embryonic cells
develop in the same order and in similar patterns
to produce homologous structures.
Vestigial Organs
• Organs with little
or no function.
• May have been
organs used in
ancestors, but no
longer needed to
survive or
reproduce.
• Examples:
Human appendix,
legs on skinks,
hip bone in
whales
Founders effect
• Founder effect – change in the allele
frequencies as a result of the migration of
a small subgroup of a population
• Speciation in the Galapagos finches
occurred by founding of a new population,
geographic isolation, changes in the new
population’s gene pool, reproductive
isolation and ecological competition.
• Members of a
sexually-reproducing
species are able to
interbreed, produce
fertile offspring, and
have a shared gene
pool
• Gene pool refers to
the collective group of
alleles of all the
individuals in a
population
• Different species do
not exchange genes
with each other by
interbreeding
Speciation
• Speciation - Formation of a new species.
• Speciation is the final result of changes in gene
pool allelic and genotypic frequencies
• Isolation
– Behavioral isolation (can mate, but do not due to
behavior)
– Geographic isolation (separated by barriers)
– Temporal isolation (reproduce at different times)
• Natural selection on single-gene traits lead to
changes in allele frequencies and therefore
evolution.
Variation and Gene Pools
• Gene Pool - All genes that are present in
a population.
• Evolution is any change in the relative
frequency of alleles in a population.
• Variation is the raw material for
evolutionary change
• Features that make an organism suited for
its environment so it can survive,
reproduce, & pass its alleles onto its
offspring are called adaptations
Genetic Drift
Genetic drift refers to changes in allele frequencies of a
gene pool due to chance (random) events
Sources of
Genetic Variation
–Mutations
–Gene shuffling (crossing over
during meiosis)
–Polygenic traits
Macroevolution
Large scale patterns of change over
long periods of time.
• Extinction – disappearance of a species
• Adaptive Radiation – a single species evolved
into several different species
• Convergent evolution – unrelated organisms
evolve similarities when adapting to similar
environments
• Coevolution – two species evolve in response
to one another
• Punctuated equilibrium – long stable periods
are interrupted by brief periods of rapid change
Cladogram – diagram that shows
evolutionary relationships among a
group of organisms