Chapter 13 1 2 SPECIES How Populations Evolve …profwelday.weebly.com/uploads/2/3/0/0/23005790/lec_ch13.pdf · 1 CHARLES DARWIN AND THE ORIGIN OF SPECIES • Biology came of age

© 2013 Pearson Education, Inc.Lectures by Edward J. Zalisko

PowerPoint® Lectures forCampbell Essential Biology, Fifth Edition, andCampbell Essential Biology with Physiology,

Fourth Edition– Eric J. Simon, Jean L. Dickey, and Jane B. Reece

Chapter 13Chapter 13How Populations Evolve

1 CHARLES DARWIN AND THE ORIGIN OF SPECIES

• Biology came of age on November 24, 1859.

Charles Darwin published On the Origin of Species

by Means of Natural Selection, an assemblage of

facts about the natural world.

© 2013 Pearson Education, Inc.

2

• Darwin made three observations from these facts.

1. Life shows rich diversity.

2. There are similarities in life that allow the classification of organisms into groups nested within broader groups.

3. Organisms display many striking ways in which they are suited for their environments.

CHARLES DARWIN AND THE ORIGIN OF SPECIES


3 Figure 13.1

(a) The diversity of life

(b) Patterns of similarities

(c) An insect suited toits environment

4

Figure 13.1c

(c) An insect suited toits environment

5

• In The Origin of Species, Darwin

– proposed a hypothesis, a scientific explanation for his observations,

– used hundreds of pages in his book to describe the evidence supporting his hypothesis,

– made testable predictions, and

– reported the results of numerous experiments he had performed.



6

• Darwin hypothesized that

– present-day species are the descendents of ancient ancestors that they still resemble in some ways and

– change occurs as a result of “descent with modification,” with natural selection as the mechanism.



7 Figure 13.2 8

• Natural selection is a process in which organisms

with certain inherited characteristics are more likely

to survive and reproduce than are individuals with

other characteristics.

• As a result of natural selection, a population, a

group of individuals of the same species living in

the same place at the same time, changes over

generations.



9

• Natural selection leads to evolutionary adaptation,

a population’s increase in the frequency of traits

suited to the environment.

• Natural selection thus leads to evolution, seen

either as

– a change in the genetic composition of a population over time or

– on a grander scale, the entire biological history, from the earliest microbes to the enormous diversity of organisms that live on Earth today.



10

• Natural selection leads to

– a population (a group of individuals of the same species living in the same place at the same time) changing over generations and

– evolutionary adaptation.

• In one modern definition of evolution, the genetic

composition of a population changes over time.



11 Darwin’s Cultural and Scientific Context

• The Origin of Species was fundamentally different

from the prevailing scientific and cultural views of

Darwin’s time.

• Let’s place Darwin’s ideas in their historical

context.


12

The Idea of Fixed Species

• The Greek philosopher Aristotle held the belief that species are fixed and do not evolve.

• The Judeo-Christian culture fortified this idea with

– a literal interpretation of the biblical book of Genesis and

– the suggestion that Earth may only be 6,000 years old.

• Naturalists were grappling with the interpretation of fossils, imprints or remains of organisms that lived in the past.


13 Figure 13.3

(a) “Snakestone” (b) Ichthyosaur skull and paddle-like forelimb

14

Lamarck and Evolutionary Adaptations

• Naturalists compared fossil forms with living

species and noted patterns of similarities and

differences.

• In the early 1800s, French naturalist Jean Baptiste

Lamarck suggested that life evolves, and explained

this evolution as the refinement of traits that equip

organisms to perform successfully in their

environment.


15

• Lamarck suggested a mechanism that we now

know is wrong.

• Lamarck proposed that by using or not using its

body parts, an individual may develop certain traits

that it passes on to its offspring, thus, acquired

traits are inherited.

• Lamarck helped set the stage for Darwin by

proposing that species evolve as a result of

interactions between organisms and their

environment.

Lamarck and Evolutionary Adaptations


16

The Voyage of the Beagle

• Darwin was born on February 12, 1809, the same

day that Abraham Lincoln was born.

• In December 1831, Darwin left Great Britain on the

HMS Beagle on a five-year voyage around the

world.


17 Figure 13.4

Darwin in 1840

NorthAmerica

Great Britain Europe Asia

Africa

SouthAmerica

Cape of Good Hope

Cape Horn

Tierra del Fuego

Australia

Tasmania

New Zealand

HMS Beagle

ATLANTICOCEAN

PACIFICOCEAN

EquatorEquator

PACIFICOCEAN

Fernandina

Isabela

Pinta

Marchena

Santiago

PinzónDaphne Islands

Genovesa

FlorenzaEspañola

SantaCruz

SantaFe San

Cristobal

40 km

40 miles

0

0

GalápagosIslands

18

• On his journey on the Beagle, Darwin

– collected thousands of specimens and

– observed various adaptations in organisms.



19

• Darwin was intrigued by

– the geographic distribution of organisms on the Galápagos Islands and

– similarities between organisms in the Galápagos and those in South America.



20

• Darwin was strongly influenced by the writings of

geologist Charles Lyell.

• Lyell suggested that Earth

– is very old and

– was sculpted by gradual geological processes that continue today.



21

• Darwin reasoned that the extended time scale

would allow for gradual changes to occur

– in species and

– in geologic features.



22

Descent with Modification

• Darwin made two main points in The Origin of

Species.

1. Organisms inhabiting Earth today descended from ancestral species.

2. Natural selection is the mechanism for descent with modification.


23 EVIDENCE OF EVOLUTION

• Evolution leaves observable signs.

• We will examine five of the many lines of evidence

in support of evolution:

1. the fossil record,

2. biogeography,

3. comparative anatomy,

4. comparative embryology, and

5. molecular biology.


24

The Fossil Record

• Fossils are

– imprints or remains of organisms that lived in the past

– often found in sedimentary rocks.


25 The Fossil Record

• The fossil record

– is the ordered sequence of fossils as they appear in rock layers,

– reveals the appearance of organisms in a historical sequence, and

– fits with the molecular and cellular evidence that prokaryotes are the ancestors of all life.


26

Figure 13.6 27 Figure 13.7-1 29

Figure 13.7-2 30 Figure 13.7-3 31

Biogeography

• Biogeography, the study of the geographic

distribution of species, first suggested to Darwin

that today’s organisms evolved from ancestral

forms.

• Darwin noted that Galápagos animals resembled

species of the South American mainland more than

they resembled animals on similar but distant

islands.


32

• Many examples from biogeography would be

difficult to understand, except from an evolutionary

perspective.

• One example is the distribution of marsupial

mammals in Australia.

Biogeography


33

Figure 13.8

Commonringtailpossum

Red kangaroo

Common wombat

Australia

Koala

34 Comparative Anatomy

• Comparative anatomy

– is the comparison of body structure between different species and

– attests that evolution is a remodeling process in which ancestral structures become modified as they take on new functions.


35

Comparative Anatomy

• Homology is

– the similarity in structures due to common ancestry and

– illustrated by the remodeling of the pattern of bones forming the forelimbs of mammals for different functions.


36 Figure 13.9

Human Cat Whale Bat

37

• Vestigial structures

– are remnants of features that served important functions in an organism’s ancestors and

– now have only marginal, if any, importance.

Comparative Anatomy


38 Comparative Embryology

• Early stages of development in different animal

species reveal additional homologous

relationships.

– For example, pharyngeal pouches appear on the side of the embryo’s throat, which

– develop into gill structures in fish and

– form parts of the ear and throat in humans.

– Comparative embryology of vertebrates supports evolutionary theory.


39

Figure 13.10

Post-analtail

Chicken embryo

Pharyngealpouches

Human embryo

40 Molecular Biology

• The hereditary background of an organism is

documented in

– its DNA and

– the proteins encoded by the DNA.

• Evolutionary relationships among species can be

determined by comparing

– genes and

– proteins of different organisms.


41

Figure 13.11

Percent of selected DNA sequences that match a chimpanzee’s DNA

Chimpanzee

100%96%92%

Human

Gibbon

Orangutan

Gorilla

Primate

Old Worldmonkey

42 NATURAL SELECTION

• Darwin noted the close relationship between

adaptation to the environment and the origin of

new species.

• The evolution of finches on the Galápagos Islands

is an excellent example.


43

Figure 13.12

(a) The large ground finch

(b) The warbler finch (c) The woodpecker finch

44 Darwin’s Theory of Natural Selection

• Darwin based his theory of natural selection on two

key observations.

1. All species tend to produce excessive numbers of offspring.

2. Organisms vary, and much of this variation is heritable.


45

• Observation 1: Overproduction and competition

– All species have the potential to produce many more offspring than the environment can support.

– This leads to inevitable competition among individuals.

Darwin’s Theory of Natural Selection


46

• Observation 2: Individual variation

– Variation exists among individuals in a population.

– Much of this variation is heritable.



47

Figure 13.14 48

• Inference: Unequal reproductive success(natural selection)

– Those individuals with traits best suited to the local environment generally leave a larger share of surviving, fertile offspring.



49

Natural Selection in Action

• Examples of natural selection include

– pesticide-resistant insects,

– antibiotic-resistant bacteria, and

– drug-resistant strains of HIV.


50


Blast Animation: Natural Selection

Select “Play”

51

Figure 13.15-1

Chromosome with geneconferring resistanceto pesticide

Insecticide application52 Figure 13.15-2


Insecticide application53

Figure 13.15-3


Reproduction

Survivors

Insecticide application54 Evolutionary Trees

• Darwin saw the history of life as analogous to a

tree.

– The first forms of life on Earth form the common trunk.

– At each fork is the last common ancestor to all the branches extending from that fork.

– The tips of millions of twigs represent the species living today.


55

Figure 13.17

Tetrapodlimbs

Amnion

Feathers

Lungfishes

Mammals

Amphibians

Lizardsand snakes

Crocodiles

Hawks and other birds

Ostriches

Am

nio

tes

Tetra

po

ds

Bird

s

Common ancestor oflineages to the right

Homologous traitshared by all groupsto the right

2

1

3

4

6

5

56 THE MODERN SYNTHESIS: DARWINISM MEETS GENETICS

• The modern synthesis is the fusion of

– genetics with

– evolutionary biology.


57

Populations as the Units of Evolution

• A population is

– a group of individuals of the same species, living in the same place at the same time and

– the smallest biological unit that can evolve.


58 Figure 13.18

(a) Two dense populations oftrees separated by a lake

(b) A nighttime satellite view of North America

59

• The total collection of alleles in a population at any

one time is the gene pool.

• When the relative frequency of alleles changes

over a number of generations, evolution is

occurring on its smallest scale.

Populations as the Units of Evolution


60 Genetic Variation in Populations

• Individual variation abounds in all species.

– Not all variation in a population is heritable.

– Only the genetic component of variation is relevant to natural selection.


61

• Variable traits in a population may be

– polygenic, resulting from the combined effects of several genes, or

– determined by a single gene.

• Polygenic traits tend to produce phenotypes that

vary more or less continuously.

• Single-gene traits tend to produce only a few

distinct phenotypes.

Genetic Variation in Populations


62 Sources of Genetic Variation

• Genetic variation results from processes that both

involve randomness:

1. mutations, changes in the nucleotide sequence of DNA, and

2. sexual recombination, the shuffling of alleles during meiosis.


63

Sources of Genetic Variation

• For any given gene locus, mutation alone has little

effect on a large population in a single generation.

• Organisms with very short generation spans, such

as bacteria, can evolve rapidly with mutation as the

only source of genetic variation.


64 Analyzing Gene Pools

• A gene pool

– consists of all the alleles in a population at any one time and

– is a reservoir from which the next generation draws its alleles.

• Alleles in a gene pool occur in certain frequencies.


65

• Alleles can be symbolized by

– p for the relative frequency of the dominant allele in the population,

– q for the frequency of the recessive allele in the population, and

– p + q = 1.

• Note that if we know the frequency of either allele

in the gene pool, we can subtract it from 1 to

calculate the frequency of the other allele.

Analyzing Gene Pools


66 Figure 13.20 70

Figure 13.21

Allele frequencies

Genotype frequencies

Sperm

Eggs

p ==== 0.8(R)

q ==== 0.2(r)

p ==== 0.8

R

q ==== 0.2

r

RR

p ==== 0.8

R

q ==== 0.2

r

p2==== 0.64

rR pq ==== 0.16 q2

==== 0.04 rr

pq ==== 0.16 Rr

(RR)

p2==== 0.64 q2

==== 0.04

(rr)2pq ==== 0.32

(Rr)

71 MECHANISMS OF EVOLUTION

• The main causes of evolutionary change are

– genetic drift,

– gene flow, and

– natural selection.

– (sexual selection is a form of natural selection)

• Natural selection is the most important, because it

is the only process that promotes adaptation.


72

Genetic Drift

• Genetic drift is a change in the gene pool of a

small population due to chance.


73


Bioflix Animation: Mechanisms of Evolution

74


Animation: Causes of Evolutionary Change

Right click slide / select “Play”

75 Figure 13.23-1

RR

rr

Rr

RR

RR

RR Rr

RR

Rr

Rr

Generation 1p ==== 0.7q ==== 0.3

76

Figure 13.23-2

Only 5 of 10plants leave

offspring

RR

rr

Rr

RR

RR

RR

RR Rr

RR

Rr

Rr

rr RR

Rr

rr

RR

Rr

Rr Rr

rr

Generation 1p ==== 0.7q ==== 0.3

Generation 2p ==== 0.5q ==== 0.5

77 Figure 13.23-3


offspring

RR

rr

Rr

RR

RR

RR

RR Rr

RR

Rr

Rr


offspring

RR

rr RR

Rr

rr

RR

Rr

Rr Rr

rr

RR

RR

RR

RR

RR

RR

RR

RR RR

Generation 1p ==== 0.7q ==== 0.3

Generation 2p ==== 0.5q ==== 0.5

Generation 3p ==== 1.0q ==== 0.0

78

The Bottleneck Effect

• The bottleneck effect

– is an example of genetic drift and

– results from a drastic reduction in population size.

• Passing through a “bottleneck,” a severe reduction

in population size,

– decreases the overall genetic variability in a population because at least some alleles are lost from the gene pool, and

– results in a loss of individual variation and hence adaptability.


79 Figure 13.24-1

Originalpopulation

80

Figure 13.24-2

Originalpopulation

Bottleneckevent

81 Figure 13.24-3

Originalpopulation

Bottleneckevent

Survivingpopulation

82

• Cheetahs appear to have experienced at least two

genetic bottlenecks:

1. during the last ice age, about 10,000 years ago, and

2. during the 1800s, when farmers hunted the animals to near extinction.

• With so little variability, cheetahs today have a

reduced capacity to adapt to environmental

challenges.

The Bottleneck Effect


83 Figure 13.25 84

The Founder Effect

• The founder effect is likely when a few individuals

colonize an isolated habitat.

• This represents genetic drift in a new colony.

• The founder effect explains the relatively high

frequency of certain inherited disorders in some

small human populations.


85 Figure 13.26

SouthAmerica

Tristan da Cunha

Africa

86

Gene Flow

• Gene flow

– is another source of evolutionary change,

– is separate from genetic drift,

– is genetic exchange with another population,

– may result in the gain or loss of alleles, and

– tends to reduce genetic differences between populations.


87 Figure 13.27 88

Natural Selection: A Closer Look

• Of all causes of microevolution, only natural

selection promotes adaptation.

• Evolutionary adaptation results from

– chance, in the random generation of genetic variability, and

– sorting, in the unequal reproductive success among the varying individuals.


89 Evolutionary Fitness

• Relative fitness is

– the contribution an individual makes to the gene pool of the next generation

– relative to the contributions of other individuals.


90

Figure 13.28 91 Three General Outcomes of Natural Selection

• If we graph the coat color of a population of mice,

we get a bell-shaped curve.

• If natural selection favors certain fur-color

phenotypes,

– the populations of mice will change over the generations and

– three general outcomes are possible.


92

1. Directional selection shifts the overall makeup

of a population by selecting in favor of one

extreme phenotype.

2. Disruptive selection can lead to a balance

between two or more contrasting phenotypic

forms in a population.

3. Stabilizing selection favors intermediate

phenotypes, occurs in relatively stable

environments, and is the most common.

Three General Outcomes of Natural Selection


93 Figure 13.29

(a) Directional selection (b) Disruptive selection (c) Stabilizing selection

Originalpopulation

Evolvedpopulation

Originalpopulation

Phenotypes (fur color)

Fre

qu

en

cy o

fin

div

idu

als

94

Figure 13.UN11

Originalpopulation

Evolvedpopulation

Pressure ofnatural selection

Directional selection Disruptive selection Stabilizing selection

95 Sexual Selection

• Sexual selection is a form of natural selection in

which individuals with certain traits are more likely

than other individuals to obtain mates.

• Sexual dimorphism is a distinction in appearance

between males and females not directly associated

with reproduction or survival.


96

Figure 13.30

(a) Sexual dimorphism in a finch species (b) Competing for mates

97 Evolution Connection: An Evolutionary Response to Malaria

• We can see the results of past natural selection in

present-day humans.

• Malaria first emerged as a serious threat to people

in Africa just 10,000 years ago,

– long after humans had established populations around the globe,

– therefore only producing evolutionary responses in malarial regions.


98

• Sickle hemoglobin

– is a mutation that denies the malarial parasite essential access to human hemoglobin and

– distorts the shape of red blood cells.

• Individuals with one copy of this sickle allele

(heterozygotes) are relatively resistant to malaria.

• Individuals with two copies (homozygotes) are

usually fatally ill.

Evolution Connection: An Evolutionary Response to Malaria


99

• In the African tropics,

– malaria is most common and

– the frequency of the sickle-cell allele is highest.

Evolution Connection: An Evolutionary Response to Malaria


100

Figure 13.31

Areas with highincidence ofmalaria

Frequencies of thesickle-cell allele

0–2.5%

10.0–12.5%

2.5–5.0%

5.0–7.5%

7.5–10.0%

>>>>12.5%

Co

lori

ze

d S

EM

Africa

Asia

101 Figure 13.UN09

Individualvariation

Overproductionof offspring

Observations

Conclusion

Natural selection:unequal reproductive success

102

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Chapter 13 1 2 SPECIES How Populations Evolve …profwelday.weebly.com/uploads/2/3/0/0/23005790/lec_ch13.pdf · 1 CHARLES DARWIN AND THE ORIGIN OF SPECIES • Biology came of age