Chapter 16 Evolution
Chapter 16 Evolution
ESSENTIAL QUESTIONS
Who was Charles Darwin and what is his
theory of Natural Selection
What is Evolution and how do mutations
allow it to happen?
Are humans still evolving?
Why or Why not?
Why is the concept of Evolution just a
theory and not considered a Scientific Law?
What is the difference between these two
types of Scientific Certainty?
Chapter 16 Evolution
•
Charles Darwin is the father of
evolutionary theory!
•
MUTATIONS are natural
changes in organisms,
occasionally(very rarely,)
they’re beneficial.
•
Humans are still evolvinghere’s a photo of me from high
school. Just
kidding…INDIVIDUALS
can’t evolve!
….but our species is.
•
Evolution is a theory but some
believe it may be the most
influential in modern scientific
thought because of its very
broad implications
Emergence of Evolutionary Thought
•Evolution is the process by which SPECIES change over time.
A Theory is a BROAD explanation that has been tested and supported.
•Like most theories, evolutionary theory keeps developing and expanding.
Most of Darwin’s ideas remain scientifically supported.
The Emergence of Evolutionary Thought
Early Explanations of life’s diversity
If species were individually and perfectly
created at one time and one place
Then….
Why were organisms different in different
regions of earth?
Why are current organisms different from
ancient organisms?
If each species is different, why are there the
same fundamental structures and body plans
to do different things in animals?
Charles Darwin 1809-1882
Charles Darwin was the NATURALIST
aboard the HMS Beagle. His job was to
collect animals and plants for
identification and potential commercial
value.
The Beagle’s mission was to map the
ports of South America. They left in 1831
and returned FIVE years later in 1836.
Young bull
Charles Darwin 1809-1882
Darwin witnessed a tremendous diversity of animal life both
living and FOSSILIZED
He traveled to the Galapagos Islands and collected a bunch
of different birds, but it turned out they were all FINCHES!
He became convinced that species change over time
Old bull
Darwin’s Influences
Darwin was influenced by a number of
Scientists and their thoughts including:
Jean Baptiste Lamarck
Thomas Malthus
Charles Lyell & James Hutton
Georges Cuvier
Darwin’s Influences: Jean Baptiste Lamarck
Lamarckian Inheritance
Lamarck noticed that each organism is usually
well ADAPTED to its environment.
He proposed that organisms change over time
as they adapt to changing environments.
Darwin once accepted this idea because it
proposed a role for inheritance in evolution.
Larmack thought early Giraffes stretched their
necks to feed and they’re newly acquired Long
neck was then passed off to
offspring…..WRONG!!!
Acquired traits are not hereditable
(or are they?)
Lamarckian Inheritance
Some of Lamacks ideas still have relevance today
though and he may be right in a way…check out
Epigenetics for an extra credit project!
Darwin’s Influences: Thomas
Malthus
Malthus:
“The tragedy of the
COMMONS”
Populations tend to grow
faster than the food supply
needed to feed it
Darwin’s Influences:
Charles Lyell & James Hutton
Lyell & Hutton- GRADUALISM
Changes occur over vast periods of time in
geology; land formations move and topography
changes
Darwin’s Influences:
Georges Cuvier
Cuvier - CATASTROPHISM
Geologic changes occur rapidly and have
catastrophic outcomes for living things,
…..like extinction
Darwin’s Theory: DESCENT with
Modification
Darwin’s Dangerous Idea:
He didn’t publish his findings until he was 50!
“On the Origin of Species” 1859
Evolutionary pathway resembled a branched tree
NOT a ladder from lower forms to higher forms
All CONTEMPORARY
species have
descended
from earlier species
Darwin’s Observations
Individuals in a population VARY, some of these variations are
inheritable
Populations produce more OFFSPRING than the environment’s
food, space, and other assets.
Therefore, species COMPETE for resources
EVOLUTION BY NATURAL SELECTION
Evolution is a change in the inherited characteristics
of a population from one generation to the next.
Darwin’s theory predicts that;
Over time, the number of individuals that carry
ADVANTAGEOUS traits will increase in a population.
Every living thing has the potential to produce many offspring, but
not all of those offspring are likely to SURVIVE and reproduce.
-Individuals that have traits that suit their environment are more
likely to survive.
-Individuals that have certain traits tend to produce more offspring
than others do.
-These differences are part of natural selection.
The Mechanism of Natural Selection
Selection and Adaptation
Darwin’s theory explains why
living things vary in form and
match their environment.
Each HABITAT presents
unique challenges and
opportunities to survive and
reproduce.
So, each species evolves
because of the “selection” of
those individuals that survive
the challenges or make best
use of the opportunities.
The Mechanism of Natural Selection
Put another way, each species becomes
adapted to its environment as a result of
living in it over time.
An ADAPTATION is an inherited trait that
is present in a population because the trait
helps individuals survive and reproduce in
a given environment.
Darwin’s theory explains evolution as a
gradual process of adaptation.
Note that Darwin’s theory refers to
populations and species—not individuals—
as the units that evolve.
–Also, keep in mind that a species is a
group of populations that can
INTERBREED.
DARWINS THEORY OF EVOLUTION BY
NATURAL SELECTION
4 Steps in Darwin’s Theory of Evolution by Natural Selection.
Step 1 Overproduction: Every population is capable of producing more
offspring than can possibly survive.
Step 2 Variation: Variation exists within every population. Much of this
variation is in the form of inherited traits.
Step 3 Selection: In a given environment, having a particular trait can
make individuals more or less likely to survive and have successful
offspring. So, some individuals leave more offspring than others do.
Step 4 Adaptation: Over time, those traits that improve survival and
reproduction will become more common.
The Mechanism of Natural Selection
VOCABULARY PART I
CHARLES DARWIN : The Father of Evolution through Natural Selection he observed change thorugh
DESCENT WITH MODIFICATION
SPECIES : Organisms so similar they can interbreed and produce VIABLE (fertile) offspring
NATURAL SELECTION: greater reproductive success displayed by individuals with ADAPTIVE traits
VARIATION: differences within a population
ADAPTATIONS: traits that are selected for because they help an organism survive and reproduce
EVOLUTION: Changes ins species over time- Occurs when genes in a population change- shift to enhance
survival and reproduction
JEAN BAPTISTE LAMARCK: Observed organisms change/evolve by passing down AQUIRED TRAITS
LYELL AND HUTTON: Geologists who proposed GRADUALISM as the source of change
CUVIER: Geologist who proposed CATASTROPHISM as the source of change
EVIDENCE FOR EVOLUTION: Comes from Fossils, Comparative Anatomy, Embryology, Biochemistry,
Biogeography, and others !
Evidence for Evolution
Evidence for Evolution comes from
each of the following disciplines
The Fossil Record
Biogeography
Development Biology or
Embryology
Comparative Anatomy
Biochemistry
Evidence for Evolution
A Fossil is a record of an animal
that is preserved in rock
Found in SEDIMENTARY Rock
Fossils show overall structural
scheme of how organism evolved
Including:
Body scheme
Feeding behavior
Mobility
Social Structure
New fossils in upper layers, older
fossils in lower layers
Evidence for Evolution
Evidence from the fossil
record allows us to piece
together an Evolutionary
SEQUENCE
The Evolutionary
Sequence of Modern
Cetacea (Whales)
Social Structure
New fossils in upper
layers, older fossils in
lower layers
Comparative
Anatomy
HOMOLOGOUS Structure:
Similar structures in related
organisms suggests organisms
share a common ancestor
Deer
vs
Kangaroo
Human Hand = Whale flipper
ANALOGOUS Structures
Similar structures in nonrelated
organisms show evolution recreates
similar solutions to different
environmental challenges
Vestigial Organs
CONTEMPORARY Organs with no apparent
use, but resemble functional structures in
ancestors
Tailbones
Wisdom Teeth
Appendix
Whale Pelvis
Comparative Embryology
Ontogeny Recapitulates Phylogeny- Organisms with common descent have similar organs
Embryos undergo many physical and genetic changes as they develop into mature forms.
Scientists compare the EMBRYONIC development of species to look for similar patterns and
structures. Such similarities most likely derive from an ancestor that the species have in common.
For example, at some time during development, all vertebrate embryos have a tail. Vertebrates
are animals that have backbones.
Vertebrates breathe though lungs but as embryos, all vertebrates have gills that becomes the
Eustachian tube in man
Biochemistry
To explain the patterns of change seen in
anatomy, scientists make testable predictions.
For example, if species have changed over time,
the GENES that determine their characteristics
should also have changed.
Genes can change by mutation and that such
change can make new varieties appear.
A comparison of DNA or amino-acid sequences
shows that some species are more genetically
similar than others. Chimps –Humans 99%
Homology
These comparisons, like those in anatomy, are
evidence of hereditary relationships among the
species.
Biogeography
Study of species distribution on
Galapagos Islands look similar to
South American species
Each island would have to had it own
special creation event for each
species.
Darwin contended one species
MIGRATED from South America
and underwent Adaptive Radiation
How Do Variations Arise?
•Natural selection IS NOT the cause of
variation
•Mutation - Random changes in DNA
sequences in the parents genome
•Gene Shuffling - mixing of parental
chromosomes can create new genetic
combinations
•Variation arises randomly. Variations are
then SELECTED on by nature.
•Variations which are selected for are called
ADAPTATIONS
Adaptations and Speciation
Types of Adaptations
STRUCTURAL Adaptations:
Involve structure or anatomy
Bird’s beak, Anteaters sticky tongue
PHYSIOLOGICAL Adaptations:
Functions in organisms
Poison Venom in a snake, ink of an octopus
BEHAVIORAL Adaptations:
Behavior aids in survival and reproduction
Wildebeasts/ Caribou/ Bird Migration
Wolves Hunt in Packs
Fish swim in schools
Species & Speciation
Species: A group of organisms that
are so similar they can interbreed
and produce FERTILE offspring
Some Organisms are similar enough
to form Hybrids-they can breed but
the offspring is infertile
Horses + Donkey = Mule
Lion + Tiger = Liger
…Not the same species but a
HYBRID
Human male + human female =
human baby…same species!
3 Types of Natural Selection
Directional Selection
Shifts a population toward one extreme
form of a trait
Stabilizing Selection:
Shifts a population toward intermediate
(medium) traits
Disruptive Selection:
Extreme phenotypes are more common
3 Types of Natural Selection
DIRECTIONAL
Selection
Shifts a population toward one
extreme form of a trait
4 million years ago; heavy cheetahs
Over time, light, fast animals
reproduced more successfully
Natural selection favored the genes
that pushed the cheetah’s weight in
one direction…lighter
Or the Human Brain…it has
continued to grow larger with more
convolutions (gyrii) over time
3 Types of Natural Selection
STABILIZING
Selection:
Shifts a population
toward intermediate
(medium) traits
Example: Most
human babies weight
~ 7pounds
3 Types of Natural Selection
DISRUPTIVE
Selection:
Extreme phenotypes are more
common
Example: African butterflies appear
as either bright orange or bright
blue
These colors mimic other
butterflies that are foul-tasting; less
likely to be eaten
Intermediate butterflies look like
neither, and are more likely to be
eaten
Patterns of Evolution
SPECIATIONOrganisms which are separated by distance + gene pool will no
longer interbreed. Each group becomes new species
Species become dissimilar or more alike over time
through gradual Change
5 Types of Evolution
Divergent Evolution:
Adaptive Radiation:
Convergent Evolution:
Coevolution
Extinction
Patterns of Evolution
Divergent Evolution:
Single population is split into 2 or more
populations.
Patterns of Evolution
Convergent Evolution:
2 dissimilar species evolve in
ways to make them LOOK
more similar
Sugar Gliders- winged
marsupials in Australia
Flying Squirrels - Winged
squirrels in Northern
Hemisphere
Flying Squirrel
Sugar Glider
Patterns of Evolution
COEVOLUTION
Organisms are part of one other’s
environment, so they can affect one
another’s evolution. Species that live in
close contact often have clear adaptations to
one another’s existence.
ADAPTIVE RADIATION
Over time, species may split into two or
more lines of descendants, or lineages. The
process tends to speed up when a new
species enters an environment that contains
few other species. (FINCHES)
EXTINCTION
If all members of a lineage die off or simply
fail to reproduce, the lineage is said to be
extinct. The fossil record shows 99% of all
species have become EXTINCT.
The Pace of Evolution and Earth History
Gradualism:
Over time, new species arise as
environment change
If true, we should see intermediate
species in fossil record…not always
true
Catastrophism:
Rapid catastrophic events shape
earth and living thing
THE CURRENT ACCEPTED THEORY
Punctuated Equilibrium:
Species exist for long periods of time without
changes, then large changes occur over short
periods of time
Populations & Evolution
Larger populations tend to have more
genetic variation
Smaller populations tend to have less
genetic variation
Genetic Drift/Founder Effect- Loss of
genetic variation due small population
sizes.
Extinction more likely
10,000 years ago, almost all cheetahs go
extinct due to climate changes. Resulting
cheetahs have little genetic diversity
Artificial Selection
The Mechanism of Natural Selection
VOCABULARY PART II
EVIDENCE FOR EVOLUTION
FOSSIL EVIDENCE: Records of past organisms show common ancestry
COMPARATIVE ANATOMY: the study of similarities in organisms of common ancestry
Vestigial Structures- appendix, whale pelvis
Analogous Structures – bee wing v. bird wing
Homologous structure - your hands-whale flipper
EMBRYOLOGY: The study of how embryos develop to show common ancestry- you had gills and a tail!
BIOCHEMISTRY: The similarity in gene sequence
BIOGEOGRAPHY: The study of how organisms are distibuted today and in the fossil record
3 TYPES OF ADAPTATIONS
STRUCTURAL ADAPTATIONS: Physical feature like a wing to fly or fins to swim
PHYSIOLOGICAL ADAPTATION: Body functions like the production of venom or the ability to tolerate heat
BEHAVIORAL ADAPTATION: When organisms work together like a wolf pack, or school of fish
3 TYPES OFNATURAL SELECTION
DIRECTIONAL SELECTION: When a direction in phenotypes is favored- bigger brains
STABILIZING SELECTION: When 1 average phenotype is selected for – 7 lb babys
DISRUPTIVE SELECTION: When 2 extreme phenotypes are selected for simultaneously- different colored butterflies
SPECIATION: The formation of new species through evolution
5 TYPES OF EVOLUTION
DIVERGENT: When new species are formed that have different features- Tiger & Lion
CONVERGENT: When species change to be similar to other species- Kangaroo & Deer
ADAPTIVE RADIATION: When species form to fill new or open ecological niches- Darwin’s Finches
COEVOLUTION: When species evolve together and rely on one another for survival- birds & flowers
EXTINCTION: When species evolutionary sequence ends-99% of all species over time have become extinct
Chapter 17 Population Genetics and
Speciation
KEY IDEAS
How is microevolution studied?
How is phenotypic variation measured?
How are genetic variation and change measured?
How does genetic variation originate?
POPULATION GENETICS
How is microevolution studied?
Microevolution can be studied by observing
changes in the numbers and types of alleles in
populations.
The study of microevolution in this sense is
POPULATION genetics.
GENETICS AND EVOLUTION
Charles Darwin knew that heredity influences
characteristics, but he did know about GENES.
We can now study and predict genetic variation
and change that underlie evolution.
MICROEVOLUTION
Microevolution or POPULATION GENETICS is
evolution at the level of genetic change in
populations.
The study of genetics and evolution are
advancing together.
The link from microevolution to
macroevolution—SPECIATION can be studied
in detail.
PHENOTYPIC VARIATION
How is phenotypic variation measured?
Biologists study polygenic phenotypes by measuring each
INDIVIDUALS in the population and then analyzing the distribution of
the measurements.
The variety of phenotypes that exists for a given characteristic depends
on how many genes affect it.
PHENOTYPIC VARIATION
Polygenic TRAITS or characters are influenced by several genes. Examples
include human eye color and height.
A distribution is an overview of the relative frequency and range of a set of
values.
Often, some values in a range are more common than others.
A normal distribution, or BELL curve, is one that tends to cluster around an
average value in the center of the range.
MEASURING VARIATION AND
CHANGE
How are genetic variation and change measured?
Genetic variation and change are measured in terms of the ALLELE
FREQUENCY in the GENE POOL of a population.
A frequency is the proportion or ratio of a group that is of one type. To
study genetic change, the frequency of each allele in a population can
be tracked over time.
The particular combination of alleles in a population at any one point in
time makes up a gene pool.
WHAT IS THE ALLELE FREQUENCY FOR THE b eye color gene in
your class??
SOURCES OF GENETIC
VARIATION
How does genetic variation originate?
The major source of new alleles in natural populations is
MUTATION in Gametes or “germ cells.”
Evolution cannot proceed if there is no variation.
Mutation generates new alleles at a slow rate.
Only mutations in germ cells (egg and sperm) are passed
on to offspring.
https://www.youtube.com/watch?v=L-cxg8mF_Lw
Section 2: Genetic Change
KEY IDEAS
What does the Hardy-Weinberg principle predict?
How does sexual reproduction influence evolution?
Why does population size matter?
What are the limits of the force of natural selection?
What patterns can result from natural selection?
EQUILIBRIUM AND CHANGE
What does the Hardy-Weinberg principle predict?
The Hardy-Weinberg principle predicts that the
frequencies of alleles and genotypes in a population
will NOT change unless at least one of five forces
acts upon the population.
The forces that can act against GENETIC
EQUILIBRIUM are gene flow, nonrandom mating,
genetic drift, mutation, and natural selection.
HARDY WEINBERG
EQUILIBRIUM
A population in which no genetic change occurred
would be in a state of genetic equilibrium.
Genetic change in a population can be measured as
a change in genotype frequency or ALLELE
FREQUENCY.
A change in one doesn’t necessarily mean a change
in the other.
THE FIVE CONDITIONS OF HARDY WEINBERG
EQUILIBRIUM
1. GENE FLOW
Gene flow occurs when genes are
added to or removed from a
population.
Gene flow can be caused by
MIGRATION, the movement of
individuals from one population to
another.
THE FIVE CONDITIONS OF HARDY WEINBERG
EQUILIBRIUM
2. NON RANDOM MATING
In sexually reproducing populations, any
limits or preferences of MATE choice will
cause nonrandom mating.
THE FIVE CONDITIONS OF HARDY
WEINBERG EQUILIBRIUM
3. GENETIC DRIFT
Chance events can cause RARE
alleles to be lost from one
generation to the next, especially
when populations are small.
Such random effects on allele
frequencies are called
GENETIC DRIFT
THE FIVE CONDITIONS OF HARDY WEINBERG
EQUILIBRIUM
4. MUTATION
Mutation can add a new ALLELE to a population.
5. NATURAL SELECTION
Natural selection acts to eliminate individuals with
certain traits from a population.
As individuals are eliminated, the alleles for those
traits may become less frequent in the population.
Thus, both allele and genotype frequencies may
change.
HOW LONG WOULD HE LAST ON THE
SAVANNAH??
SEXUAL REPRODUCTION AND
EVOLUTION
How does sexual reproduction influence evolution?
Sexual reproduction creates the possibility that mating patterns
or behaviors can influence the gene pool of a population.
For example, in animals, females sometimes select mates
based on the male’s size, color, ability to gather food, or other
characteristics.
This kind of behavior is called sexual selection and is an
example of nonrandom mating.
SEXUAL REPRODUCTION AND
EVOLUTION
Another example of nonrandom
mating is INBREEDING, in
which individuals either selffertilize or mate with others like
themselves.
Inbreeding is more likely to
occur if a population is small. In
a small population, all members
are likely to be closely related.
POPULATION SIZE AND
EVOLUTION
Why does population size matter?
Allele frequencies are more likely to remain stable in LARGE
populations than in small populations.
Population size strongly affects the probability of genetic change in a
population.
Genetic drift is a strong force in small populations and occurs
when a particular allele DISAPPEARS.
NATURAL SELECTION AND
EVOLUTION
What are the limits of the force of natural
selection?
Natural selection acts only to change the relative
frequency of alleles that exist in a population. It
acts on genotypes by removing
UNSUCCESSFUL phenotypes from a
population.
NATURAL SELECTION AND
EVOLUTION
Natural selection is a result of the following
facts:
–All populations have genetic variation.
–Individuals tend to produce more OFFSPRING
than the environment can support.
–Populations depend upon the reproduction of
individuals.
Genetic Results of Selection
The result of natural selection is that each allele’s
frequency may increase or decrease depending
on the allele’s effects on survival and
reproduction.
Although natural selection is not the only force
that can cause evolution, it is a powerful force.
Why Selection is Limited
The key lesson that scientists have learned about
evolution by natural selection is that the
ENVIRONMENT does the selecting.
Only characteristics that are expressed can be
targets of natural selection. If a mutation results in
rare recessive alleles, for example, selection cannot
operate against it.
For this reason, genetic disorders (such as cystic
fibrosis in humans) can persist in populations.
PATTERNS OF NATURAL
SELECTION
What patterns can result from
natural selection?
Three major patterns are possible
in the way that natural selection
affects the distribution of
polygenic characters over time.
These patterns are Directional
selection, Stabilizing selection,
and Disruptive selection
Directional Selection
In directional selection, the
“peak” of a normal
distribution moves in one
direction along its range.
In this case, selection acts to
eliminate on extreme from a
range of phenotypes, making
them less common.
Stabilizing Selection
In stabilizing selection, the bellcurve shape becomes
NARROWER.
In this case, selection eliminates
individuals that have alleles for
any extreme type.
Stabilizing selection is very
common in nature.
•Disruptive Selection
In disruptive selection, the bell
curve is “disrupted” and pushed
apart into TWO peaks.
In this case, selection acts to
eliminate individuals with average
phenotype values.
Section 3: Speciation
KEY IDEAS
How can species be defined?
How do we know when new species have
been formed?
Why is studying extinction important to
understanding evolution?
DEFINING SPECIES
A species is generally
defined as a POPULATION
that can interbreed and
usually produce fertile
offspring.
Other definitions for species
may be used for fossils or for
organisms that reproduce
asexually. Species may be
instead be defined based on
their physical features, their
ecological roles, and their
genetic relatedness.
FORMING NEW SPECIES
How do we know when new species
have been formed?
Speciation has occurred when the
net effects of evolutionary forces
result in a population that has
unique features and is
REPRODUCTIVELY isolated.
SPECIATION
Each population of a single species lives in a different place.
In each place, natural selection acts upon each population and tends to result in
offspring that are better adapted to each specific environment.
If the ENVIRONMENTS differ, the adaptations may differ. This is called divergence
and can lead to the formation of new species.
Speciation is the process of forming new species by evolution from preexisting species
Reproductive Isolation
Reproductive isolation is a state in which two populations can no longer
interbreed
From this point on, the groups may be subject to different forces, so they will
tend to diverge over time.
Through divergence over time, populations of the same species may differ
enough to be considered SUBSPECIES.
Subspecies are simply populations that have taken a step toward speciation
REPRODUCTIVE ISOLATION
Any of the following mechanisms may
contribute to the reproductive isolation of
populations:
Geography
Ecological Niche
Mating Behavior and Timing
Polyploidy
Hybridization
EXTINCTION: THE END OF
SPECIES
Why is studying extinction important to
understanding evolution?
The species that exist at any time are the net result
of both speciation and extinction.
Extinction occurs when a species fails to produce
any more descendants. Extinction, like speciation,
can only be detected after it is complete.
EXTINCTION THE END OF
SPECIES
More than 99% of all of the species that have
ever lived becoming extinct.
Many cases of extinction are the result of
ENVIRONMENTAL change.
If a species cannot adapt fast enough to changes,
the species may be driven to extinction.
CH17 VOCAB
BIO CH17 VOCAB
Chapter 17 Population Genetics and Speciation
• MICROEVOLUTION: the study of changes in allele frequency of a population
• POPULATION: A group of organism of the same species that are breeding
• PHENOTYPIC VARIATION: the allele frequencies within a population
• NORMAL DISTRIBUTION: the bell curve
• ALLELE FREQUENCY: the ratio of specific alleles in a population
• GENETIC VARIATION: the different forms of alleles and traits in a population
HARDY WEINBERG EQUILIBRIUM: an IDEAL condition in which no evolution or
allele frequency change occurs - when all of the following DO NOT HAPPEN
•
•
•
•
•
GENE FLOW: the gain or loss of new alleles through immigration or emmigration
MUTATION: change in DNA sequence
NONRANDOM MATING:reproductive selection, females choose mates selectively
GENETIC DRIFT: small populations can have major changes in allele frequency
NATURAL SELECTION: when the environment favors a particular allele over
another
CH17 VOCAB
BIO CH17 VOCAB Chapter 17 Population Genetics and Speciation
•FOUNDER EFFECT: the initial alleles/individuals in a population have great
effect on allele frequency
•POPULATION SIZE: the larger the population the smaller the impact of
individual changes in allele frequency
•SPECIATION: the development of new species through directional,
disruptive or stabilizing selection
•REPRODUCTIVE ISOLATION: a barrier to reproduction amoung
individuals that leads to new species
– Geography: physical barriers like rivers, canyons, oceans –squirrels in grand
canyon
– Ecological Niche: organisms are performing different roles in an ecosystem –
Darwin Finches
– Mating Behavior and Timing: migrations, mating dances in birds
– Polyploidy: changes in chromosome number
– Hybridization : pairings between similar species- liger