Transcript Charles Darwin Notes

Charles Darwin
and the
Theory of Evolution
Charles Darwin’s Voyage of the
Beagle
Galapagos Islands
Even though
these islands
are close
together they
varied greatly in
their climates
Amount of rainfall,
vegetation
differences,
different species!
Darwin’s Observations
• The plants and animals were wellsuited to their environment
Example: A Cactus is adapted to live in dry areas
• Species vary in traits and some
traits are better suited for different
areas
Darwin’s Finches
• The beaks were
•
different from island
to island
Beaks were better
suited for feeding
depending upon
location (islands)
Darwin’s Tortoises
• Due to differences
in plant life;
Darwin noticed
that tortoises had
differences in
SHELL shape and
NECK lengths
15-2
Jean-Baptiste Lamarck
• One of the first scientists to
•
•
•
notice living things have
changed over time
Proposed that by selective use
or disuse of organs, organisms
acquired or lost certain traits
during their lifetimes
These traits could then be
passed on to their offspring
Do you agree with this theory?
Darwin Presents His Case-1859
In this book, Darwin
proposed the concept of
EVOLUTION by the method
of NATURAL SELECTION.
Evolution is?
Natural Selection is?
Speciation is?
Explain how these relate?
Evolution by Natural Selection
• Struggle for Existence
Each species will compete for food, space, basic
needs
• Survival of the Fittest/Natural Selection
Fitness=able to survive and reproduce!
• Descent with Modification
The “fittest” reproduce thus passing on their
GREAT traits!
Adaptations
A inherited characteristic that increases an
organisms chance of survival.
Examples:
1.Anatomical/stuctural- porcupines sharp quills,
camouflage, mimicry
2.Behavioral- mating rituals
3.Physiological-plant performing photosynthesis
Evolution occurs in Populations
*not individuals*
But what is a population?
*A group of inter-breeding
species
Evolution of Populations
• Genetic variation is studied in populations
(group of same species that interbreed)
• Gene pool – all genes that are present in a
population
• Relative frequency – number of times an
allele occurs in a gene pool, compared with the
number of times other alleles for the same gene
occur
How do we know when
Evolution has occurred?
A change in the relative frequency of alleles
in a population
48%
heterozygous
black
36%
homozygous
brown
allele for
brown fur
allele for
black fur
16%
homozygous
black
60% or 30/50=brown allele
Genetic Variation in Populations
• Two main sources of genetic variation
– Mutations
• Change in a sequence of DNA
– Gene shuffling
• Independent movement of chromosomes during
meiosis and Crossing-Over
3 Causes of Evolution
1. Genetic Drift: change in the gene pool due
to chance (small populations will be greatly
affected)
A. Bottleneck Effect- over hunting,
earthquake, fire etc…
*this can lead to endangered species!
B. Founder Effect- small group leaves
the source population to establish their own
Example:Polydactyly in Amish that came
to the United States (they carried the allele)
3 Causes of Evolution
con’t
2. Gene Flow:
Fertile immigrants or emigrants bringing or
taking alleles from the population
Example: If your 2nd period class has all blue
eyed people (bb) and someone comes in that has
brown eyes (BB)
3 Causes of Evolution
con’t
• Natural Selection:
Well suited organisms increase their chance
of surviving thus reproducing to pass on
their genes (alleles) to the next generation
Example: Peppered
Moth example
Single-Gene and Polygenic
Traits
• The number of phenotypes produced for a trait
depends on how many genes control the trait
– Single-gene trait
• Single gene with
two alleles
• Fewer phenotypes
than polygenic
traits
• Ex: widow’s peak
– Polygenic trait
• Controlled by two or
more genes (each
with more than 2
alleles)
• Many different
genotypes and
phenotypes
• Ex: height
Natural Selection acts on
Polygenic Traits 3 ways
Directional Selection
Disruptive Selection
Stabilizing Selection
Genetic Equilibrium
• If a population was to not evolve, or
change, the population would reach
equilibrium – when allele frequencies stay
the same
• Conditions required to reach equilibrium:
– Random mating
– Large population
– No movement in or out of population
– No mutations
– No natural selection
Speciation
• Isolation prevents interbreeding between
populations
– Behavioral isolation
• Different courtship rituals or reproductive
strategies
– Geographic isolation
• Two populations are separated by geographic
barriers (rivers, mountains, oceans, etc..)
– Temporal isolation
• Species reproduce at different times (winter –vsspring)