Biology · The Origin of Species By Means of Natural Selection • The Origin of Species focused biologists’ attention on the great diversity of organisms, whereby Darwin noted

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology

Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

BIG IDEA I The process of evolution drives

the diversity and unity of life. Enduring Understanding 1.A

Change in the genetic makeup of a population over time is evolution.

Essential Knowledge 1.A.1

Natural selection is a major mechanism of evolution.


Essential Knowledge 1.A.1: Natural selection is a major mechanism of evolution.

• Learning Objectives:

– (1.1) The student is able to convert a data set from a

table of numbers that reflect a change in the genetic

makeup of a population over time and to apply

mathematical methods and conceptual understandings

to investigate the cause(s) and effect(s) of this change.

– (1.2) The student is able to evaluate evidence provided

by data to qualitatively and quantitatively investigate

the role of natural selection in evolution.

– (1.3) The student is able to apply mathematical

methods to data from real or simulated populations to

predict what will happen to the population in the future.


Overview: Endless Forms Most Beautiful

• A new era of biology began in 1859 when Charles Darwin published On The Origin of Species By Means of Natural Selection

• The Origin of Species focused biologists’ attention on the great diversity of organisms, whereby Darwin noted that current species are descendants of ancestral species

• Evolution can be defined by Darwin’s phrase descent with modification, and can be viewed as both a pattern and a process



Darwin’s Two Major Points from Origin of Species

1. The manuscript presented evidence that many species of organisms presently inhabiting the Earth are descendants of ancestral species (common descent)

2. The manuscript proposed a mechanism for the evolutionary process (natural selection)

a population’s allele frequency can change over generations if individuals that possess certain heritable traits leave more offspring than others

results in evolutionary adaptation – accumulation of inherited characteristics that enhance organisms’ ability to survive and reproduce in specific environments

evolution – change over time in genetic composition of a population and could eventually lead to new species



According to Darwin’s theory of natural selection, competition for limited resources results in differential survival.

• Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations.



Fig. 22-UN1

Observations

Over time, favorable traits accumulate in the population.

Inferences

and

Individuals in a population vary in their heritable

characteristics.

Organisms produce more offspring than the

environment can support.

Individuals that are well suited to their environment tend to leave

more offspring than other individuals


Evolutionary fitness is measured by reproductive success.


FITNESS is measured as

REPRODUCTIVE success.

Natural selection is differential

success in reproduction - it

results from the interaction

between individuals that vary in

heritable traits and their

environment.


Genetic variation and mutation play roles in natural selection.

• A diverse gene pool is important for the survival of a species in a changing environment.

• Two processes, mutation and sexual reproduction,

produce the variation in gene pools that contributes to

differences among individuals:

– Variation in individual genotype leads to variation in

individual phenotype.

– Not all phenotypic variation is heritable.

– Natural selection can only act on variation with a

genetic component.


Fig. 23-2

(a) (b)


Mutation

• Mutations are changes in the nucleotide sequence of DNA

• Mutations cause new genes and alleles to arise

• Only mutations in cells that produce gametes can be

passed to offspring

A A A

A A

A A A

A A A

a a

A a A A a

T = 0 T = 1


Point Mutations

• A point mutation is a change in one base in a gene

• The effects of point mutations can vary:

– Mutations in noncoding regions of DNA are often

harmless

– Mutations in a gene might not affect protein production

because of redundancy in the genetic code

– Mutations that result in a change in protein production

are often harmful

– Mutations that result in a change in protein production

can sometimes increase the fit between an organism

and the environment


Types of Point Mutations


Mutations That Alter Gene Number or Sequence

• Chromosomal mutations that delete, disrupt, or

rearrange many loci are typically harmful:

– Duplication of large chromosome segments

is usually harmful.

– Duplication of small pieces of DNA is

sometimes less harmful and increases the

genome size.

– Duplicated genes can take on new

functions by further mutation.


Types of Chromosomal Mutations


Sexual Reproduction http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

• Sexual reproduction can shuffle existing alleles into new combinations.

• In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible.

• Three mechanisms contribute to the shuffling of alleles during sexual reproduction:

– Crossing over

– Independent assortment of alleles

– Fertilization

http://www.sumanasinc.com/webcontent/animations/content/meiosis.html


Environments can be more or less stable, and this affects evolutionary rate and direction.

• Different genetic variations can be selected in

each generation.


An adaptation is a genetic variation that is favored by natural selection.

• It is manifested as a trait that provides an advantage

to an organism in a particular environment.


Natural Selection: A Summary

1. Overpopulation - more organisms are born than can survive

2. Variation within a population - there will be many variation

for different traits among individuals

3. Competition within the population - individuals will compete

for survival: food, mates, shelter, etc.

4. Survival of the Fittest - those with traits best suited to the

environment will be more likely to survive

5. Reproduction - individuals that survive will pass their traits

on to the next generation

6. Adaptive Evolution – over time, specialized traits that

enhance survival and reproduction accumulate in a

population. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations.

• Natural selection is NOT the only mechanism

responsible for evolution.

• Although natural selection is usually the major

mechanism for evolution, genetic variation in

populations can occur through other processes:

– Mutation, genetic drift, sexual selection and artificial

selection can all contribute to the evolution of a

population.

– Inbreeding, small population size, nonrandom

mating, the absence of migration, and a net lack of

mutations can lead to loss of genetic diversity.


Genetic Drift http://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation45.html

• The smaller a sample, the greater the chance of deviation from a predicted result.

• Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next.

• Genetic drift tends to reduce genetic variation through losses of alleles.

• REAL WORLD EXAMPLES OF GENETIC DRIFT:

1. The Bottleneck Effect

2. The Founder Effect

http://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation45.html




Fig. 23-8-3

Generation 1

CW CW

CR CR

CR CW

CR CR

CR CR

CR CR

CR CR

CR CW

CR CW

CR CW

p (frequency of CR) = 0.7

q (frequency of CW ) = 0.3

Generation 2

CR CW CR CW

CR CW

CR CW

CW CW

CW CW

CW CW

CR CR

CR CR

CR CR

p = 0.5

q = 0.5

Generation 3

p = 1.0

q = 0.0

CR CR

CR CR

CR CR

CR CR

CR CR

CR CR CR CR

CR CR

CR CR CR CR


The Hardy-Weinberg equation can be used to test whether a population is evolving.

• Mathematical approaches are used by scientists to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.

– A population is a localized group of individuals capable of interbreeding and producing fertile offspring.

– A gene pool consists of all the alleles for all loci in a population.

– A locus is fixed if all individuals in a population are homozygous for the same allele.


Genetic Equilibrium and Hardy-Weinberg

• Hardy-Weinberg Principle – states that allele frequencies tend to remain constant in populations unless something happens OTHER THAN Mendelian segregation and sexual recombination.

– This situation in which allele frequencies remain constant is called genetic equilibrium.

– If allele frequencies do not change, the population will not evolve!

• Hardy-Weinberg is a mathematical model that describes the changes in allele frequencies in a population:

– Allows us to predict allele and genotype frequencies in subsequent generations (testable).

– Allows us to determine whether or not a population is evolving (mathematically supported evidence of evolution).


• By convention, if there are 2 alleles at a locus,

p and q are used to represent their frequencies

– p = frequency of dominant allele in

population

– q = frequency of recessive allele in

population

• The frequency of all alleles in a population will

add up to 1

– For example, p + q = 1

Calculating Allele Frequencies


Model Assumptions and the Hardy-Weinberg Principle

• Model Assumptions: conditions required to

maintain genetic equilibrium (no evolution)

from generation to generation:

1. Randomly Mating Population

2. Large Population Size (n>100)/No Genetic Drift

3. No Immigration or Emigration/Restrict Gene Flow

4. No Mutations

5. No Natural Selection


Variables of the Hardy-Weinberg Equation

• Let p= frequency of the dominant allele

• Let q= frequency of the recessive allele

• Let p2= frequency of the homozygous dominant genotype

• Let 2pq= frequency of the heterozygous genotype

• Let q2= frequency of homozygous recessive genotype

• Law says, given assumptions, that within 1 generation of random mating, the genotype frequencies are found to be in the binomial distribution p2+2pq+q2=1 (genotype frequencies) and p+q=1 (allele frequencies)


Application of the Hardy-Weinberg Equilibrium Equation

• The allele for the ability to roll one’s tongue is

dominant (R) over the allele for the lack of this

ability (r).

• In a population of 500 individuals, 25% show the

recessive phenotype. How many individuals

would you expect to be homozygous dominant

and heterozygous?

– The equation: p2 + 2pq + q2 = 1

– Therefore, p + q = 1


Graphical Analysis of Allele Frequencies in a Population



Biology

Eighth Edition







Natural selection acts on phenotypic variations in populations.


Essential Knowledge 1.A.2: Natural selection acts on phenotypic variations in populations.


– (1.4) The student is able to evaluate data-based

evidence that describes evolutionary changes in the

genetic makeup of a population over time.

– (1.5) The student is able to connect evolutionary

changes in a population over time to a change in the

environment.


Environments change and act as selective mechanisms on populations.

• The environment is always changing, there is no

“perfect” genome, and therefore a diverse gene pool is

necessary for the long-term survival of species.

– Genetic variations within a population contribute to the

diversity of the gene pool.

– Changes in genetic information may be silent, or result in

a new phenotype (positive, negative or neutral).

– The interaction of the environment and the phenotype

determines the fitness of the phenotype.

– Thus, the environment does NOT direct changes in

DNA, but acts upon existing that occur through random

changes in DNA.


• Natural selection does not create new traits,

but edits or selects for traits already present in

the population.

• The local environment determines which traits

will be selected for or selected against in any

specific population.

• Because environments change, they act as

selective mechanisms on populations.

– Illustrative Example: peppered moth


Phenotypic variations ARE NOT directed by the environment but occur through RANDOM changes in the DNA and through new gene combinations.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Illustrative Example: The Peppered Moth


Some phenotypic variations significantly increase or decrease fitness of the organism and the population.

• Illustrative Examples:

– Peppered Moth

– DDT Resistance in Insects

– Sickle Cell Anemia


Evolution of Insecticide Resistance


1. By spraying crops with poisons to

kill insects, humans have

unwittingly favored the reproductive

success of insects with inherent

resistance to poisons.

2. Resistant individuals survive and

reproduce, passing the gene for

resistance to offspring.

3. Additional applications of the same

insecticide will be less effective,

and the frequency of resistant

insects in the population will grow.

READ ARTICLE: The Exterminator-

Pesticides & Resistance

Red blood cells are able to transport oxygen because

they are filled with a protein called hemoglobin, which

picks up oxygen in the lungs and drops it off where it

is needed in tissues and organs.

A mutated version in one of the hemoglobin genes

leads to Sickle Cell Anemia by changing the

hemoglobin protein in such a way that it tends to

clump up into long chains inside red blood cells.

Instead of maintaining the usual flexible disc-like

shape that enables them to squeeze through even the

tiniest blood vessels, the red blood cells of people

with the disease twist into stiff crescents that are not

efficient at transporting oxygen.

"Sickled" red blood cells can clog small blood vessels,

preventing oxygen from making it to certain parts of

the body. The condition is life-threatening.

READ ARTICLE: Heterozygous Advantage & Sickle Cell

Anemia

Evolution of Sickle Cell Anemia


Molecular Basis of Sickle Cell Disease

In the DNA, the mutant

template strand (top) has

an A where the wild type

template has a T.

The mutant mRNA has a

U instead of an A in one

codon.

The mutant (sickle cell)

hemoglobin has a valine

(Val) instead of a glutamic

acid (Glu).

This mutation causes the

hemoglobin protein to be

inproperly shaped.


Heterozygous Advantage & Sickle Cell Anemia

• In the United States, one in every 500 African-American births and one

out of every 1,000 to 1,400 Hispanic births is affected by Sickle Cell

Anemia. Another two million Americans carry the sickle cell trait.

• As devastating as the disease can be, it turns out there is a reason

Sickle Cell Anemia is so common and has NOT been “weeded out” of

the human population.

• Usually a DNA change that causes a serious disease quickly gets

pushed out of a population's gene pool. But researchers have found

that the version of the gene that causes Sickle Cell Anemia has been

around for thousands of years.

• That observation, and the fact that this version is mainly found in

people with ancestors who lived relatively recently in Africa, the

Mediterranean, India, or the Middle East, led scientists to wonder if the

Sickle Cell Anemia-causing version of the gene offers some kind of

benefit to people living in those regions.

Sickle Cell and Resistance to Malaria

• That benefit turned out to be

resistance to malaria. Malaria is

caused by parasites that multiply

inside of human red blood cells.

Because the disease can only be

transferred from person to person by

mosquitoes, it is confined to areas of

the world where the insects thrive.

• Every year malaria infects more than

300 million people and kills more than

a million, particularly young children.

• Carriers of the sickle cell trait are to a

large extent resistant to malaria.

Compared to non-carriers, they have

approximately 1/10 the risk of dying

from infection by the most deadly

species of malaria parasite.

• Nevertheless, carriers are not

completely protected from the disease

and experts recommend that they still

take precautions against malaria.


Heterozygous Advantage & Sickle Cell Anemia

• Over the years, carriers living in malaria-ridden locales

would have had a survival benefit compared to non-

carriers, allowing them to live longer and have more

children.

• This benefit is what evolutionary biologists call

"heterozygote advantage," and it explains why the sickle

cell trait has persisted in areas where malaria is common.

• The price for the carriers' advantage, though, is that some

of their children are born with Sickle Cell Anemia.

Fig. 23-17

0–2.5%

Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote)

Frequencies of the sickle-cell allele

2.5–5.0%

7.5–10.0%

5.0–7.5%

>12.5%

10.0–12.5%

Mapping Malaria

&

Sickle Cell Disease


Humans impact variation in other species.

• Illustrative Examples:

– Artificial Selection

– Overuse of Antibiotics

Fig. 22-9

Kale

Kohlrabi

Brussels sprouts

Leaves

Stem

Wild mustard

Flowers

and stems

Broccoli

Cauliflower

Flower

clusters

Cabbage

Terminal

bud Lateral

buds


Human Impact on Genetic Variation

Fig. 22-UN2

INQUIRY CHALLENGE

Mosquitoes resistant to the pesticide DDT first appeared in India in 1959, but

now are found throughout the world.

a. Graph the data in the table above.

b. Examine the graph and hypothesize why the percentage of mosquitoes resistant

to DDT rose rapidly.

c. Suggest an explanation for the global spread of DDT resistance.

Fig. 22-UN3



Biology

Eighth Edition







Evolutionary change is also driven by random processes.


Essential Knowledge 1.A.3: Evolutionary change is also driven by random processes.


– (1.6) The student is able to use data from

mathematical models based on the Hardy-Weinberg

equilibrium to analyze genetic drift and effects of

selection in the evolution of specific populations.

– (1.7) The student is able to justify data from

mathematical models based on the Hardy-Weinberg

equilibrium to analyze genetic drift and the effects of

selection in the evolution of specific populations.

– (1.8) The student is able to make predictions about the

effects of genetic drift, migration and artificial selection

on the genetic makeup of a population.


Remember: The process of evolution drives the diversity and unity of life.

• Evolution is a change in the genetic makeup

of a population over time with natural

selection its major driving mechanism.

– Darwin’s theory, supported by evidence from many

disciplines, states that inheritable variations occur in

individuals in a population.

– Due to competition for limited resources, individuals

with more favorable variations are more likely to

survive and produce more offspring, thus passing

traits to future generations.

– Individuals do not evolve, but rather populations evolve.


Remember: Natural selection is not the only mechanism responsible for evolution.

• Although natural selection is usually the

major mechanism for evolution, genetic

variation in populations can occur through

other processes:

– Mutation, genetic drift, sexual selection and

artificial selection can all contribute to the

evolution of a population.

– Inbreeding, small population size, nonrandom

mating, the absence of migration, and a net lack of

mutations can lead to loss of genetic diversity.


Overview: The Smallest Unit of Evolution

• Focusing on evolutionary change in

populations, we can define evolution on its

smallest scale, called microevolution.

– Microevolution involves evolutionary changes below

the species level; changes in allele frequencies in a

population over generations.

– Our focus in this section will be to understand that

natural selection is not the only cause of

microevolution.

– The other two mechanisms include genetic drift and

gene flow.


Genetic drift is a nonselective process occurring in small populations.

• The smaller a sample, the greater the chance of deviation from a predicted result.

• Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next.

• Genetic drift tends to reduce genetic variation through losses of alleles.


Sample of

Original Population

Founding Population A

Founding Population B

Descendants

The Founder Effect http://bcs.whfreeman.com/thelifewire/content/chp24/2402002.html

http://bcs.whfreeman.com/thelifewire/content/chp24/2402002.html


The Bottleneck Effect

Fig. 23-10

Number of alleles per locus

Range of greater prairie chicken

Pre-bottleneck (Illinois, 1820)

Post-bottleneck (Illinois, 1993)

Minnesota, 1998 (no bottleneck)

Nebraska, 1998 (no bottleneck)

Kansas, 1998 (no bottleneck)

Illinois

1930–1960s

1993

Location Population size

Percentage of eggs hatched

1,000–25,000

<50

750,000

75,000– 200,000

4,000

5.2

3.7

93

<50

5.8

5.8

5.3 85

96

99

(a)

(b)


Reduction of the genetic variation within a given population can increase the differences between populations of the same species.

• Upon arrival to Galapagos, organisms were identical to their ancestors

on the mainland of S. America.

• Random loss of genetic variation over time increased the differences

between the island dwellers and their ancestors.


Effects of Genetic Drift: A Summary

1. Genetic drift is significant in small populations

2. Genetic drift causes allele frequencies to

change at random

3. Genetic drift can lead to a loss of genetic

variation within populations

4. Genetic drift can cause harmful alleles to

become fixed

5. Genetic drift can facilitate inbreeding – which

leads to further reduction in variation


• Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions.

• Only natural selection consistently results in adaptive evolution!

• Natural selection brings about adaptive evolution by acting on an organism’s phenotype, NOT genotype.

• The phrases “struggle for existence” and “survival of the fittest” are misleading as they imply direct competition among individuals, BUT reproductive success is generally more subtle and depends on many factors.

• Natural selection occurs in three ways: stabilizing selection, directional selection, and disruptive selection.

Natural selection is the only mechanism that consistently causes adaptive evolution.


Directional, Disruptive, and Stabilizing Selection http://bcs.whfreeman.com/thelifewire/content/chp23/2302001.html

• Three modes of selection:

– Directional selection favors individuals at one

end of the phenotypic range

– Disruptive selection favors individuals at both

extremes of the phenotypic range

– Stabilizing selection favors intermediate

variants and acts against extreme phenotypes

http://bcs.whfreeman.com/thelifewire/content/chp23/2302001.html

Fig. 23-13a

Original population

(a) Directional selection

Phenotypes (fur color)

Original population

Evolved population

Fig. 23-13b

Original population

(b) Disruptive selection


Evolved population

Fig. 23-13c

Original population

(c) Stabilizing selection


Evolved population


The Key Role of Natural Selection in Adaptive Evolution

• Natural selection increases the frequencies of alleles that enhance survival and reproduction.

• Adaptive evolution occurs as the match between an organism and its environment increases.

• Because the environment can change, adaptive evolution is a continuous process.

• Genetic drift does not consistently lead to adaptive evolution as they can increase or decrease the match between an organism and its environment.



Biology

Eighth Edition







Biological evolution is supported by scientific evidence

from many disciplines, including mathematics.


Essential Knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics.


– (1.9) The student is able to evaluate evidence provided by data

from many scientific disciplines that support biological evolution.

– (1.10) The student is able to refine evidence based on data from

many scientific disciplines that support biological evolution.

– (1.11) The student is able to design a plan to answer scientific

questions regarding how organisms have changed over time

using information from morphology, biochemistry and geology.

– (1.12) The student is able to connect scientific evidence from

many disciplines to support the modern concept of evolution.

– (1.13) The student is able to construct and/or justify mathematical

models, diagrams or simulations that represent processes of

biological evolution.


Direct Evidence for Evolution

• Evolution is supported by an overwhelming amount

of scientific evidence from geographical, geological,

physical, chemical and mathematical applications.

• New discoveries continue to fill the gaps identified by

Darwin in The Origin of Species.

• Two examples provide direct evidence for natural

selection:

1. the effect of differential predation on guppy

populations;

2. and the evolution of drug-resistant HIV


Fig. 22-13

Predator: Killifish; preys

mainly on juvenile

guppies (which do not

express the color genes)

Guppies: Adult males have

brighter colors than those

in “pike-cichlid pools”

Experimental transplant of guppies

Pools with

killifish,

but no

guppies prior

to transplant

Predator: Pike-cichlid; preys mainly on adult guppies

Guppies: Adult males are more drab in color

than those in “killifish pools”

Source

population Transplanted

population

Source

population

Transplanted

population

Nu

mb

er

of

co

lore

d s

po

ts

12 12

10 10

8 8

6 6

4 4

2 2

0 0

RESULTS

EXPERIMENT


The Evolution of Drug-Resistant HIV

• The use of drugs to combat HIV selects for

viruses resistant to these drugs

• HIV uses the enzyme reverse transcriptase to

make a DNA version of its own RNA genome

• The drug 3TC is designed to interfere and

cause errors in the manufacture of DNA from

the virus


Fig. 22-14

Weeks

Patient No. 3

Patient No. 2

Patient

No. 1

0 0

25

50

75

100

2 4 6 8 10 12


Evidence for Evolution

• Evidence that the diversity of life is a product of evolution pervades every research field of biology. Molecular, morphological and genetic information of existing and extinct organisms add to our understanding of evolution:

– Fossil Record Evidence

– Succession of Fossil Forms

– Comparative Anatomy

– Anatomical Homologies

– Embryological Homologies

– Molecular Homologies

– Biogeography

– Geographic Distribution of Species

– Continental Drift



Evidence for Evolution



How Rocks and Fossils Are Dated

• Sedimentary strata reveal the relative ages of

fossils:

– In relative dating, the order of rock strata is used to determine

the relative age of fossils. Older specimens are found in deeper

layers of strata.

• The absolute ages of fossils can be determined by

radiometric dating

– Radiometric dating uses the decay of radioactive isotopes to

determine the age of the rocks or fossils.

– It is based on the rate of decay, or half-life of the isotope (the

time required for half the parent isotope to decay).


Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human Whale Cat Bat

Morphological Homologies

Homologous structures are those found in different species that are

similar and result from common ancestry.


Fig. 22-18

Human embryo Chick embryo (LM)

Pharyngeal pouches

Post-anal tail

Comparative Embryology


The skeletons of

some snakes retain

vestiges of the

pelvis and leg bones

of walking

ancestors.

We would not

expect to see these

structures if snakes

had an origin

separate from other

vertebrate animals.

Vestigial Structures


Molecular Homologies



Convergent Evolution

• Although organisms that are closely related

share characteristics because of common

descent, distantly related organisms can

resemble one another for a different reason:

– Convergent evolution is the evolution of similar, or

analogous, features in distantly related groups.

– Analogous traits arise when groups independently

adapt to similar environments in similar ways.

– Convergent evolution does not provide information

about ancestry!



Homologous v. Analogous Structures

• Homologous structures are similar structures occurring in different species that are believed to be derived from a common ancestor.

• Analogous structures are similar structures occurring in different species that are believed to be the result of convergent evolution (similar environmental pressures).


Fig. 22-20

Sugar glider

Flying squirrel

AUSTRALIA

NORTH AMERICA


Biogeography: The Geographic Distribution of Species


Documents

Biology · The Origin of Species By Means of Natural Selection • The Origin of Species focused biologists’ attention on the great diversity of organisms, whereby Darwin noted