Download Evolution NOTES

Evolution
Part 1
Unit 10
Miss Wheeler
Evolution
›  Evolution-
The process by which
organisms have changed (and
will continue changing) over
time
›  Charles
Darwin- “Father of
Evolution”
›  Traveled for 5 years on the H.M.S
Beagle mapping the coast of
South America, during which he
collected specimens and made
observations.
Darwin’s Inspirations
›  Jean-Baptiste
Lamarck- Organisms could change
over time by selectively using body parts.
Organisms can pass these new traits on.
(INCORRECT)
›  Charles Lyell- Earth is very old and changes over
time
›  Thomas Malthus- If human population continued to
increase, there won’t be enough space/food.
Population will be forced down by war, disease,
and famine.
**So why do only some individuals survive and/or
reproduce?**
Darwin’s Observations
›  Species
vary globally
›  Different,
but similar, animal species lived in separate, but
similar, habitats around the world.
›  Species
vary locally
›  Different,
but related, animal species often lived in different
habitats within a local area.
›  Species
vary over time
›  Some
fossils of extinct animals
were similar to living species.
Darwin’s Conclusions
›  Common
Descent- Species weren’t created in
their present form, but rather they evolved
from ancestral species.
›  Natural
Selection- process by which organisms
with variations most suited to their environment
survive and leave more offspring; explanation
for evolution (change over time)
Theory of Natural Selection
1. 
2. 
3. 
Struggle of Existence- more individuals are born
than can survive; competition for food, space,
etc.
Variation & Adaptation- populations continue to
change as they become better suited for
surviving and reproducing, or as their
environment changes.
Survival of the Fittest- well-adapted individuals
survive and reproduce, passing on their
adaptations.
Natural Selection
Grasshoppers can lay more than 200 eggs at a
time, but only a small fraction of these offspring
survive to reproduce.
Natural Selection
In this population of grasshoppers, heritable variation
includes yellow and green body color. Green color is an
adaptation: The green grasshoppers blend into their
environment and so are less visible to predators.
Natural Selection
Because their color serves as a camouflage adaptation,
green grasshoppers have higher fitness and so survive
and reproduce more often than yellow grasshoppers do.
Natural Selection
Green grasshoppers become more common than yellow
grasshoppers in this population over time because more
grasshoppers are born than can survive, individuals vary in
color and color is a heritable trait, and green grasshoppers
have higher fitness in this particular environment
Common Descent
›  Over
many generations, adaptation could cause
successful species to evolve into new species.
›  All species are descended from common
ancestors but have modified/changes over time.
›  “Descent
with modification”
Evidence of Evolution-Fossils
›  Earth
is about 4.5 billion years old.
›  Fossils- traces of organisms that have been long
deceased; can be traced to modern species
Evidence of Evolution-Fossils
Recently, more than 20 related fossils have been
found that document the evolution of modern whales
from ancestors that walked on land.
Evidence of Evolution-Embryology
›  Early
developmental stages of many vertebrates
look very similar.
›  This similarity suggests that all vertebrates share a
common ancestor.
Evidence of EvolutionHomologous Structures
›  Parts
of different organisms with similar structures
that have adapted for different functions
›  Suggest common ancestry
Evidence of EvolutionAnalogous Structures
›  Parts
of different organisms with similar functions,
but different structures.
Evidence of EvolutionVestigial Organs
›  Parts
that are inherited from ancestors but have
now become unnecessary and non-functional
Evidence of EvolutionGenetic Code
›  All
living cells use info coded in DNA and RNA to
carry info from one generation to the next.
›  Genetic code is nearly identical is almost all
organisms à suggests common ancestors
Evidence of EvolutionHomologous Molecules
›  Similar
proteins between organisms
›  Similar genes- Example: Hox genes
Evolution of Populations
›  Population-
group of individuals of the same
species that live in the same area.
›  Species- a group of populations that can breed
and produce fertile offspring
›  Microevolution- small scale changes within a
population.
›  Macroevolution- changes in groups larger than
a single species over a long period of time.
Evolution of PopulationsMicroevolution
›  Gene
Pool- total collection of genes in a
population at any one time.
›  Within a gene pool, every allele has a relative
frequency (# of occurrences in that population)
›  Evolution is any change in the relative frequency
of alleles in the gene pool of a population over
time.
›  Natural selection operates on individuals, but
resulting changes in allele frequencies show up in
populations. Populations, rather than individuals,
evolve.
Evolution of PopulationsMicroevolution
For example, this diagram shows the gene pool for
fur color in a population of mice.
Mechanisms of Microevolution
Mutation
2.  Migration
3.  Non-Random Mating
4.  Genetic Drift
5.  Natural Selection
1. 
1. Mutation
› Mutations
that produce changes in
phenotype may or may not affect
fitness/survival.
› Mutations introduce new alleles into a
gene pool and change allele
frequencies.
› Mutations only matter in evolution if they
can be passed down.
2. Migration
› Gain/loss
of alleles from a population
due to the movement of individuals or
gametes.
› Individuals who immigrate into a
population may introduce new alleles
into the gene pool.
› Individuals who emigrate out of a
population may remove alleles.
3. Non-Random Mating
› Individuals
may select mates based on
heritable traits (size, color). Therefore,
some genes will be favored over others.
› Artificial Selection- selective breeding of
organisms by humans for desirable traits
(ex. Crops, dogs)
4. Genetic Drift
› Changes
in the gene pool of a small
population due to chance.
› Bottleneck effect- resulting from a
disaster that reduces population size
(volcano).
› Founder effect- resulting from
colonization of new location by small
number of individuals.
5. Natural Selection
› If
different genes have different fitness,
the pressures of natural selection will
affect the distribution of phenotypes in
population.
›  Directional
Selection
›  Stabilizing Selection
›  Disruptive Selection
5. Natural Selection
›  Directional
Selection- individuals at one end of a
distribution curve have higher fitness than others.
The range of phenotypes shift because those
individuals are more successful at surviving and
reproducing.
For example, if only
large seeds were
available, birds with
larger beaks would
have an easier time
feeding and would be
more successful in
surviving and passing on
genes.
5. Natural Selection
›  Stabilizing
Selection- individuals near the center of
the distribution curve have higher fitness than
others. This situation keeps the center of the curve
at its current position, but narrows the graph.
For example, very small
and very large babies
are less likely to survive
than average-sized
individuals. The fitness of
these smaller or larger
babies is therefore lower
than that of more
average-sized
individuals. 5. Natural Selection
›  Disruptive
Selection- individuals either end of the
distribution curve have higher fitness those in the
middle. This situation acts against those with an
intermediate type and can create two distinct
phenotypes.
For example, in an area
where medium-sized seeds
are less common, birds
with unusually small or
large beaks would have
higher fitness. Therefore,
the population might split
into two groups—one with
smaller beaks and one
with larger beaks. Speciation
›  Factors
such as natural selection and genetic
drift can change the relative frequencies of
alleles in a population, but this alone does not
lead to development of a new species. How
does speciation happen?
›  Speciation- Formation of a new species from an
old species.
›  Mechanisms:
›  Reproductive
Isolation
›  Behavioral Isolation
›  Geographic Isolation
›  Temporal Isolation
Reproductive Isolation
Speciation starts with reproductive isolation, when a
population splits into two groups and the two populations no
longer interbreed. They may evolve into 2 separate species.
This can be caused by behavioral, geographic, or temporal
isolation.
Behavioral Isolation
When two populations that are capable of interbreeding
develop differences in courtship rituals or other behaviors.
For example, eastern and western meadowlarks are similar
birds whose habitats overlap. But they won’t mate with each
other, partly because they use different mating songs.
Geographic Isolation
When two populations are physically separated by
geographic barriers such as rivers or mountains.
For example, the Kaibab squirrel is a subspecies of the Abert’s
squirrel that formed when a small population became isolated
on the north rim of the Grand Canyon. Separate gene pools
formed, and genetic changes in one group were not passed
on to the other.
Temporal Isolation
When breeding occurs at different times for different species.
For example, 3 species of orchid live in the same rain forest.
Each species has flowers that last only one day and must be
pollinated on that day to produce seeds. Because the species
bloom on different days, they cannot pollinate each other.