13 Lecture Presentation

© 2010 Pearson Education, Inc.

Lectures by Chris C. Romero, updated by Edward J. Zalisko

PowerPoint® Lectures forCampbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean DickeyCampbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey

Chapter 13

How Populations Evolve


CHARLES DARWIN AND THE ORIGIN OF SPECIES• Charles Darwin published On the Origin of Species by Means of

Natural Selection, November 24, 1859. • Darwin presented two main concepts:

– Life evolves – Change occurs as a result of “descent with

modification,” with natural selection as the mechanism.

– 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.

• 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

– Evolutionary adaptation

• In one modern definition of evolution, the genetic composition of a population changes over time.

1809Lamarck

publisheshis theory

of evolution.

1830Lyell publishes

Principles of Geology.

1837Darwin begins analyzing his

specimens and writing hisnotebooks on the origin

of species. 1844Darwin writes his essayon the origin of species.1865

Mendel publishespapers on genetics.

1858Wallace sends an

account of histheory to Darwin.

1859Darwin publishesThe Origin of Species.

1809Charles Darwinis born.

1831–36Darwin travels

around the worldon the HMS Beagle.

Green sea turtle in theGalápagos Islands

1800

1870

Figure 13.2


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 Bible and suggested the Earth may only be 6,000 years old.

• Jean Baptiste Lamarck suggested that organisms evolved by the process of adaptation by the inheritance of acquired characteristics, now known to be incorrect.


• Darwin, on his journey on the Beagle:– Collected thousands of fossil specimens – Observed various adaptations in different

organisms

• Darwin was intrigued by:– The geographic distribution of organisms on the

Galápagos Islands – Similarities between organisms in the Galápagos

and those in South America

Darwin in 1840

Galápagos Islands

NorthAmerica

South America

PACIFICOCEAN

PACIFICOCEAN

ATLANTICOCEAN

Pinta

40 miles

40 km0 Florenza

0

Fernandina

MarchenaGenovesa

EquatorSantiago

Daphne IslandsPinzón

Española

Isabela SantaCruz SantaFe San

Cristobal

Great Britain

Cape ofGood Hope

Europe

Africa

Cape Horn

Tierra del Fuego

Equator

Asia

HMS Beagle

Australia

Tasmania NewZealand

Andes

Figure 13.3

A Trinidad tree mantid that mimics dead leaves

A flower mantid in Malaysia

A leaf mantid in Costa Rica

Figure 13.1

Figure 13.4


EVIDENCE OF EVOLUTION• We will examine five of the many lines of evidence in support of evolution:– The fossil record– Biogeography– Comparative anatomy– Comparative embryology– Molecular biology


The Fossil Record• Fossils are:

– Imprints or remains of organisms that lived in the past

– Often found in sedimentary rocks

The fossil record:– Is the ordered sequence of fossils as they appear in

rock layers– Reveals the appearance of organisms in a historical

sequence– Fits the molecular and cellular evidence that

prokaryotes are the ancestors of all life


Fossils


Ice Man

The researchers analysed hair samples in excess of 5,000 years old using MALDITOF mass spectrometry. This allowed them to study patterns of peptides of fermented proteins present in the ancient hair and compare them with those of modern day animals.


• Paleontologists:– Are scientists that study fossils – Have discovered many transitional forms that link

past and present


Biogeography• Biogeography is the study of the geographic distribution of species that first suggested to Darwin that today’s organisms evolved from ancestral forms.

• One example is the distribution of marsupial mammals in Australia.

Commonringtailpossum

Red kangarooCommon wombat

AustraliaKoala

Figure 13.7


Comparative Anatomy• Comparative anatomy

– Is the comparison of body structure between different species

– Confirms that evolution is a remodeling process

• Homology is:– The similarity in structures due to common

ancestry having the same anatomy but serve different functions.

– E.g.; Illustrated by the remodeling of the pattern of bones forming the forelimbs of mammals which are considered homologous structures.

Human Cat Whale Bat

Figure 13.8


• Vestigial structures:– Are remnants of features that served important

functions in an organism’s ancestors – Now have only marginal, if any, importance. E.g.;

wisdom tooth, appendix, tail bone .


Comparative Embryology• Early stages of embryo 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 – Form parts of voice box in humans

– Presence of the tail in all vertebrates


Embryological evidence

Figure 16.9

Pharyngeal slits exist in these five vertebrate animals . . .

sea lamprey pond turtle chicken domestic cat human being

pharyngeal slits

. . . evidence that all five evolved from a common ancestor

Developmental biology ( embroyology)

Tail

Post-analtail

Human embryoChicken embryo

Pharyngealpouches

Figure 13.9


Molecular Biology• The hereditary and evolutionary background of an organism is documented in comparision done with :– DNA molecule and – The proteins encoded by the DNA

Percent of selected DNA sequencesthat match a chimpanzee’s DNA

Chimpanzee

100%96%92%

Human

Gibbon

Orangutan

Gorilla

Primate

Old Worldmonkey

Figure 13.10


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 which have evolved over time because of their food habits.

(a) The largeground finch

(b) The small tree finch (c) The woodpecker finchFigure 13.11


Darwin’s Theory of Natural Selection• Darwin based his theory of natural selection on two key observations:– All species tend to produce excessive numbers of

offspring – Organisms vary, and much of this variation is

heritable


• Observation 1: Overproduction– All species tend to produce excessive numbers.– This leads to a struggle for existence.


• Observation 2: Individual variation– Variation exists among individuals in a

population.– Much of this variation is heritable.


Natural Selection in Action• Examples of natural selection include:

– Pesticide-resistant insects– Antibiotic-resistant bacteria– Drug-resistant strains of HIV

Chromosome with geneconferring resistanceto pesticide

Reproduction

Survivors

Insecticide application

Figure 13.14-3

The Modern Synthesis: Darwinism Meets Genetics• The modern synthesis is the fusion of genetics with evolutionary biology. This aspect was not known during Darwin’s time.



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– The smallest biological unit that can evolve

(a) Two dense populations of

trees separated by a lake


• 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, which is sometimes called microevolution.


Sources of Genetic Variation• Genetic variation results from:

– Mutations, changes in the DNA of an organism– Sexual recombination, the shuffling of alleles

during meiosis

• Organisms with very short generation spans, such as bacteria, can evolve rapidly with mutations as the only source of genetic variation.


MECHANISMS OF EVOLUTION• The main causes of micro evolutionary change are:– Genetic drift– Gene flow– Natural selection


Genetic Drift• Genetic drift is:

– A change in the gene pool of a small population– Due to chance

Only 5 of10 plantsleaveoffspring

RR

rr

Rr

RR

RR

RR

RR Rr

RR

Rr

Rr

Only 2 of10 plantsleaveoffspring

RR

rr RR

Rr

rr

RR

Rr

Rr Rr

rr

RR

RR

RR

RR

RR

RR

RR

RR RR

Generation 1p (frequency of R) 0.7q (frequency of r) 0.3

Generation 2p 0.5q 0.5

Generation 3p 1.0q 0.0

Figure 13.22-3


The Bottleneck Effect• The bottleneck effect:

– Is an example of genetic drift – Results in a drastic reduction in population

size

Bottlenecking in a population usually reduces genetic variation because at least some alleles are likely to be lost from the

gene pool.Cheetahs appear to have experienced at least two

genetic bottlenecks in the past 10,000 years.

Originalpopulation

Bottleneckingevent

Survivingpopulation

Figure 13.23-3


The Founder Effect• The founder effect is likely when a few individuals colonize an isolated habitat and represent genetic drift in a new colony.

• The founder effect explains the relatively high frequency of certain inherited disorders among some small human populations.

SouthAmerica

Tristan da Cunha

Africa

Figure 13.25


Gene Flow• Gene flow:

– Is genetic exchange with another population – Tends to reduce genetic differences between

populations


Three General Outcomes of Natural Selection• Directional selection:– Shifts the phenotypic “curve” of a population – Selects in favor of one extreme phenotype

• Disruptive selection can lead to a balance between two or more contrasting phenotypic forms in a population.

• Stabilizing selection:– Favors intermediate phenotypes – Is the most common

Originalpopulation

EvolvedpopulationPhenotypes (fur color)

Freq

uenc

yof i

ndiv

iduals

Originalpopulation

(a) Directional selection(b) Disruptive selection(c) Stabilizing selectionFigure 13.28


Sexual Selection• Sexual dimorphism is:

– A distinction in appearance between males and females

– Sexual selection is a form of natural selection in which inherited characteristics determine mating preferences or combat.

Evolution Connection: The Genetics of the Sickle-Cell Allele• Sickle-cell disease:

– Is a genetic disorder – Affects about one out of every 400 African-

Americans

• Abnormally sickle shaped red blood cells cause painful and life-threatening complications. Heterozygous individuals for the sickle-cell allele:– Do not develop sickle-cell anemia – Are more resistant to malaria

• In the African tropics, where malaria is most common, the frequency of the sickle-cell allele is highest. © 2010 Pearson Education, Inc.

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%

Colo

rize

d SEM

Figure 13.30

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