Transcript Charles Darwin and Natural Selection

Charles Darwin
and
Natural Selection
Evolution Primer #2 –
Who was Charles Darwin?
Theory of Acquired Characteristics

Gain or lose
features based on
overuse or non-use
of them. Would
pass this trait onto
offspring.
Lamarck
Example



Giraffes have long
necks because they
stretched them to
reach food in high
places.
Characteristic then
passed onto
offspring.
Other Examples?
Theory Discarded
 Lamarck’s
illogical…
 Car
theory proved to be
Accident/Amputation Example
Charles Darwin



HMS Beagle
Galapagos Islands
Suspected that small
gradual changes might
lead to new species
over time.
Natural Selection

Individuals in a population show
differences, or variation.

Variations can be inherited.


Some competition would lead to the death
of some individuals while others will
survive.
Individuals that have advantageous
variations will be more likely to survive
and reproduce.
1. Individuals in a population show
differences, or variation.
2. Variations can be inherited.
3. Some competition would lead to
the death of some individuals while
others will survive.

REVIEW ALERT!
– What are some factors that organisms
compete for?
4. Individuals that have
advantageous variations will be
more likely to survive and
reproduce.
Interactive Activities:
Natural Selection
 Visualizing
 Basic
Natural Selection
Principles of Natural Selection
 Virtual
Peppered Moth Simulation
 Natural
Selection video clip
Darwin’s Galapagos Island
Observations
 Species
on the Galapagos Island
closely resembled species found on
mainland South America even
though the environments were not
very similar.
 Why
is this the case?
Darwin’s Finches

Observation:
– Finches of
Galapagos Islands
looked very similar
except for shape of
their beak.
Darwin’s observations

Organisms were
originally from
South America
 Organisms
began
to change after
leaving South
America and
arriving at the
Galapagos.
Darwin’s Finches

Conclusion:
– Finches came from
common ancestor.
– EXPLANATION:
Different shape of
beak was
adaptation for
eating a particular
food source.
Adaptations and Evolutionary
Strategies


A trait shaped by natural selection that
increases an organism’s reproductive
success.
Fitness: measure of the relative
contribution an individual trait makes to
the next generation.
– How many viable offspring does an organism
provide to the next generation?
Types of Adaptation
Camouflage
Mimicry
Compare Mimicry and Camouflage.
 Antimicrobial
Resistance
– For almost every antibiotic, at least one
species of resistant bacteria exists.
Cannibalism
Feathers
http://notesfromatransitionalfossil.blogspot.com/2008/10/itsall-over-but-crying-and-burial.html
http://www.mvsd21.org/~abrown/
Mechanisms of Evolution
 EVOLUTION
OCCURS AT THE
POPULATION LEVEL, WITH GENES
AS THE RAW MATERIAL.
Hardy-Weinberg Principle


If allele frequencies do not change, the
population will not evolve.
In order for this to happen, 5 conditions
need to be met.
1. No Genetic Drift!

Genetic Drift – change in allelic
frequencies in a population that is
due to chance.
– Founder Effect
– Bottleneck
2. No Gene Flow!
 No
new genes can enter the
population and no genes can leave
the population.
 Migration
increases genetic variation
within a population and reduces
differences between populations.
3. Mating must be random
 This
rarely ever happens…. Why?
4. No mutations
 Mutation
material.
– random change in genetic
 Mutations
can change the alleles in a
population (sometimes even for the
better).
5. No natural selection.
 HW
requires that all individuals in
population be equally adapted to
their environment and thus
contribute equally to the next
generation.
 Does
this happen!?!?
Types of Natural Selection
 Stabilizing
Selection
 Directional
Selection
 Disruptive
Selection
Stablilizing Selection
 Eliminates
extreme
expressions of a
trait when the
average
expression leads
to higher fitness.
 Example:
weight
baby
Directional Selection
 An
extreme
version of a trait
makes an
organism more
fit.
 Example:
Peppered moth
Example
Disruptive Selection
 Splits
population
into two groups:
 Removes
individuals with
average traits,
but retain
individuals
expressing
extreme traits.
Example
Speciation

A population diverges and then is
reproductively isolated.
– can no longer interbreed or produce
fertile offspring with one another
 Different
 TWO
“species” result
MAIN TYPES
– Allopatric Speciation
– Sympatric Speciation
Allopatric Speciation
A
physical barrier divides one
population into two or more
populations.
 Examples:
mountain ranges,
channels, wide rivers, lava flows
 Grand
Canyon Speciation? – Kaibab
and Albert Squirrels
Sympatric Speciation
A
species evolves into a new species
without a physical barrier. They live
side by side.
 Examples:
apple maggot flies
diverging based on fruit they eat
Patterns of Evolution
– Two or more related
species become more
and more DIFFERENT
as a result of new
habitat or
opportunity.
Red Fox
Divergent Evolution
Kit Fox

Patterns of Evolution

Convergent
Evolution
– Unrelated species
become more and
more alike in
appearance as they
adapt to the same
kind of environment
Co-evolution


The relationship
between two species
is so close that the
evolution of one
species affects the
evolution of the
other.
Ex: Moth’s foot long
tongue
Rate of Speciation
 Traits
may change rapidly or slowly.
 Rates
of Speciation:
– Gradual Equilibrium
– Punctuated Equilibrium
Rates of Speciation
Gradual Equilibrium
 Evolution
steps.
proceeds in small, gradual
 Supported
evidence.
by a great deal of
 HOWEVER,
fossil record contains
instances of abrupt transitions.
Example: snail shells
Punctuated Equilibrium
 Rapid
spurts of genetic change cause
species to diverge quickly; these
periods punctuate much longer
periods when species show little
change.
 Accounts
record.
for abrupt changes in fossil