Chapter 13 How Populations Evolve PowerPoint Lectures for

Chapter 13 How Populations Evolve PowerPoint Lectures for

Chapter 13 How Populations Evolve PowerPoint Lectures for Biology: Concepts & Connections, Sixth Edition Campbell, Reece, Taylor, Simon, and Dickey Lecture by Joan Sharp Copyright 2009 Pearson Education, Inc.

Introduction: Clown, Fool, or Simply Well Adapted? Living organisms are adapted to their environment Copyright 2009 Pearson Education, Inc. Haltere Introduction: Clown, Fool, or Simply Well

Adapted? What is an adaptation? Behavioral adaptations Structural adaptations Biochemical adaptations Physiological adaptations Copyright 2009 Pearson Education, Inc. DARWINS THEORY OF EVOLUTION

Copyright 2009 Pearson Education, Inc. 13.1 A sea voyage helped Darwin frame his theory of evolution The primary mechanism of evolutionary change producing adaptation of organisms to their environment is natural selection, the differential survival and reproduction of individuals within a population

Copyright 2009 Pearson Education, Inc. 13.1 A sea voyage helped Darwin frame his theory of evolution The Greek philosopher Aristotle viewed species as perfect and unchanging In the century prior to Darwin, the study of fossils suggested that species had changed over time Copyright 2009 Pearson Education, Inc.

13.1 A sea voyage helped Darwin frame his theory of evolution Jean Baptiste Lamarck suggested that life on Earth evolves His proposed mechanisms: Use and disuse Inheritance of acquired characteristics Video: Blue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual

Video: Galpagos Sea Lion Video: Galpagos Island Overview Video: Galpagos Tortoise Video: Galpagos Marine Iguana Video: Soaring Hawk Copyright 2009 Pearson Education, Inc.

Great Britain Europe North America ATLANTIC OCEAN Africa

PACIFIC OCEAN Brazil Equator Marchena Santiago Pinzn

Fernandina Isabela 0 0 40 km PACIFIC OCEAN

Pinta Genovesa Equator Daphne Islands SantaSanta Cruz Fe

Australia Cape of Argentina Good Hope Cape Horn San Cristobal Florenza Espaola 40 miles

South America Andes The Galpagos Islands Tasmania New

Zealand Great Britain North America Europe ATLANTIC

OCEAN Brazil Africa PACIFIC OCEAN Equator South America

Andes Australia Cape of Good Hope Argentina Cape Horn Tasmania New Zealand

The Galpagos Islands Pinta Marchena Santiago Isabela

0 Genovesa Equator Daphne Islands Pinzn Fernandina

0 PACIFIC OCEAN 40 km Santa Santa Cruz Fe Florenza

40 miles San Cristobal Espaola 13.1 A sea voyage helped Darwin frame his theory of evolution Darwin was influenced by Lyells Principles of Geology

He came to realize that the Earth was very old and that, over time, present day species have arisen from ancestral species by natural processes Copyright 2009 Pearson Education, Inc. 13.1 A sea voyage helped Darwin frame his theory of evolution In 1859, Darwin published On the Origin of Species by Means of Natural Selection,

presenting a strong, logical explanation of descent with modification, evolution by the mechanism of natural selection Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Darwin observed that Organisms produce more offspring than the environment can support

Organisms vary in many traits Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Darwin reasoned that traits that increase their chance of surviving and reproducing in their environment tend to leave more offspring than others As a result, favorable traits accumulate in a

population over generations Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Darwin found convincing evidence for his ideas in the results of artificial selection, the selective breeding of domesticated plants and animals

Copyright 2009 Pearson Education, Inc. Terminal bud Cabbage Lateral buds Flower

clusters Brussels sprouts Leaves Kale Cauliflower Stem Wild mustard Flowers

and stems Broccoli Kohlrabi 13.2 Darwin proposed natural selection as the mechanism of evolution Note these important points Individuals do not evolve: populations evolve Natural selection can amplify or diminish only heritable traits; acquired characteristics cannot

be passed on to offspring Evolution is not goal directed and does not lead to perfection; favorable traits vary as environments change Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Will natural selection act on variation in hair style in a human population?

Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Will natural selection act on tongue rolling in a human population? (Note: Tongue rolling is an inherited trait, caused by a dominant allele)

Copyright 2009 Pearson Education, Inc. 13.2 Darwin proposed natural selection as the mechanism of evolution Will natural selection act on eye number in a human population? Copyright 2009 Pearson Education, Inc. 13.3 Scientists can observe natural selection in action

Rosemary and Peter Grant have worked on Darwins finches in the Galpagos for over 20 years In wet years, small seeds are more abundant and small beaks are favored In dry years, large strong beaks are favored because large seeds remain Video: Seahorse Camouflage Copyright 2009 Pearson Education, Inc.

A flower mantid in Malaysia A leaf mantid in Costa Rica 13.3 Scientists can observe natural selection in action Development of pesticide resistance in insects Initial use of pesticides favors those few insects that have genes for pesticide resistance

With continued use of pesticides, resistant insects flourish and vulnerable insects die Proportion of resistant insects increases over time Copyright 2009 Pearson Education, Inc. Chromosome with allele conferring resistance to pesticide

Additional applications will be less effective, and the frequency of resistant insects in the population will grow Pesticide application Survivors

13.4 The study of fossils provides strong evidence for evolution The fossil record shows that organisms have evolved in a historical sequence The oldest known fossils are prokaryote cells The oldest eukaryotic fossils are a billion years younger Multicellular fossils are even more recent Video: Grand Canyon

Copyright 2009 Pearson Education, Inc. Tappania, a unicellular eukaryote Dickinsonia costata 2.5 cm A Skull of Homo erectus B Ammonite casts

C Dinosaur tracks D Fossilized organic matter of a leaf E Insect in amber F Ice Man 13.4 The study of fossils provides strong evidence for evolution

Many fossils link early extinct species with species living today A series of fossils documents the evolution of whales from a group of land mammals Copyright 2009 Pearson Education, Inc. Pakicetus (terrestrial) Rhodocetus (predominantly aquatic)

Pelvis and Dorudon (fully aquatic) hind limb Pelvis and hind limb Balaena (recent whale ancestor) Pakicetus (terrestrial) Rhodocetus (predominantly aquatic)

Pelvis and hind limb Dorudon (fully aquatic) Pelvis and hind limb Balaena (recent whale ancestor) 13.5 A mass of other evidence reinforces the evolutionary view of life

Biogeography, the geographic distribution of species, suggested to Darwin that organisms evolve from common ancestors Darwin noted that animals on islands resemble species on nearby mainland more closely than they resemble animals on similar islands close to other continents Copyright 2009 Pearson Education, Inc. 13.5 A mass of other evidence reinforces the

evolutionary view of life Comparative anatomy is the comparison of body structures in different species Homology is the similarity in characteristics that result from common ancestry Vertebrate forelimbs Copyright 2009 Pearson Education, Inc. Humerus

Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale

Bat 13.5 A mass of other evidence reinforces the evolutionary view of life Which of the following pairs are homologous structures? Human limb and whale flipper Insect wing and bat wing Human thumb and chimpanzee thumb Copyright 2009 Pearson Education, Inc.

13.5 A mass of other evidence reinforces the evolutionary view of life Which of the following are homologous structures? Oak leaf and oak root Oak leaf and lichen Oak leaf and maple leaf There are no homologous plant structures Copyright 2009 Pearson Education, Inc.

13.5 A mass of other evidence reinforces the evolutionary view of life Comparative embryology is the comparison of early stages of development among different organisms Many vertebrates have common embryonic structures, revealing homologies When you were an embryo, you had a tail and pharyngeal pouches (just like an embryonic fish)

Copyright 2009 Pearson Education, Inc. Pharyngeal pouches Post-anal tail Chick embryo

Human embryo 13.5 A mass of other evidence reinforces the evolutionary view of life Some homologous structures are vestigial organs For example, the pelvic and hind-leg bones of some modern whales Copyright 2009 Pearson Education, Inc.

Pakicetus (terrestrial) Rhodocetus (predominantly aquatic) Pelvis and Dorudon (fully aquatic) hind limb Pelvis and hind limb Balaena (recent whale ancestor)

13.5 A mass of other evidence reinforces the evolutionary view of life Molecular biology: Comparisons of DNA and amino acid sequences between different organisms reveal evolutionary relationships All living things share a common DNA code for the proteins found in living cells We share genes with bacteria, yeast, and fruit flies

Copyright 2009 Pearson Education, Inc. Head Thorax Abdomen 0.5 mm Dorsal

BODY AXES (a) Adult Anterior Left Ventral Right Posterior

13.6 Homologies indicate patterns of descent that can be shown on an evolutionary tree Darwin was the first to represent the history of life as a tree Copyright 2009 Pearson Education, Inc. 13.6 Homologies indicate patterns of descent that can be shown on an evolutionary tree Homologous structures and genes can be

used to determine the branching sequence of an evolutionary tree Copyright 2009 Pearson Education, Inc. Lungfishes Amniotes Mammals

2 Tetrapod limbs Amnion Lizards 3 and snakes 4

Crocodiles Ostriches 6 Feathers Hawks and other birds

Birds 5 Tetrapods Amphibians 1 THE EVOLUTION

OF POPULATIONS Copyright 2009 Pearson Education, Inc. 13.7 Populations are the units of evolution A population is a group of individuals of the same species living in the same place at the same time Evolution is the change in heritable traits in a population over generations Populations may be isolated from one

another (with little interbreeding), or individuals within populations may interbreed Copyright 2009 Pearson Education, Inc. 13.7 Populations are the units of evolution A gene pool is the total collection of genes in a population at any one time Microevolution is a change in the relative frequencies of alleles in a gene pool over

time Copyright 2009 Pearson Education, Inc. 13.7 Populations are the units of evolution Population genetics studies how populations change genetically over time The modern synthesis connects Darwins theory with population genetics Copyright 2009 Pearson Education, Inc.

13.8 Mutation and sexual reproduction produce genetic variation, making evolution possible Mutation, or changes in the nucleotide sequence of DNA, is the ultimate source of new alleles Occasionally, mutant alleles improve the adaptation of an individual to its environment and increase its survival and reproductive success (for example, DDT resistance in insects)

Copyright 2009 Pearson Education, Inc. 13.8 Mutation and sexual reproduction produce genetic variation, making evolution possible Chromosomal duplication is an important source of genetic variation If a gene is duplicated, the new copy can undergo mutation without affecting the function of the original copy For example, an early ancestor of mammals

had a single gene for an olfactory receptor The gene has been duplicated many times, and humans now have 1,000 different olfactory receptor genes Copyright 2009 Pearson Education, Inc. 13.8 Mutation and sexual reproduction produce genetic variation, making evolution possible Sexual reproduction shuffles alleles to produce new combinations

Homologous chromosomes sort independently as they separate during anaphase I of meiosis During prophase I of meiosis, pairs of homologous chromosomes cross over and exchange genes Further variation arises when sperm randomly unite with eggs in fertilization Animation: Genetic Variation from Sexual Recombination Copyright 2009 Pearson Education, Inc. A1

Parents A1 A2 A3

Meiosis Gametes A1 A2 A3 Random

fertilization Offspring, with new combinations of alleles A1 A2 A1

and A3 13.8 Mutation and sexual reproduction produce genetic variation, making evolution possible How many possible combinations of chromosomes are possible in a human sperm or egg due to independent assortment during meiosis?

23 combinations 46 combinations 232 = 529 combinations 223 = ~ 8 million combinations Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving Sexual reproduction alone does not lead to evolutionary change in a population

Although alleles are shuffled, the frequency of alleles and genotypes in the population does not change Similarly, if you shuffle a pack of cards, youll deal out different hands, but the cards and suits in the deck do not change Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving

The Hardy Weinberg principle states that allele and genotype frequencies within a sexually reproducing, diploid population will remain in equilibrium unless outside forces act to change those frequencies Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving Imagine that there are two alleles in a bluefooted booby population: W and w

W is a dominant allele for a nonwebbed booby foot w is a recessive allele for a webbed booby foot Copyright 2009 Pearson Education, Inc. Webbing No webbing 13.9 The Hardy-Weinberg equation can be used to

test whether a population is evolving Consider the gene pool of a population of 500 boobies 320 (64%) are homozygous dominant (WW) 160 (32%) are heterozygous (Ww) 20 (4%) are homozygous recessive (ww) Copyright 2009 Pearson Education, Inc. Phenotypes Genotypes

WW Ww ww Number of animals (total = 500) 320

160 20 Genotype frequencies 320 = 500

Number of alleles in gene pool (total = 1,000) Allele frequencies 160 = 500 0.64

640 W 800 1,000 = 0.32 160 W + 160 w 0.8 W

200 1,000 = 20 500 = 40 w 0.2 w

0.04 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving Frequency of dominant allele (W) = 80% = p 80% of alleles in the booby population are W Frequency of recessive allele (w) = 20% = q

20% of alleles in the booby population are w Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving Frequency of all three genotypes must be 100% or 1.0 p2 + 2pq + q2 = 100% = 1.0 homozygous dominant + heterozygous + homozygous recessive = 100%

Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving What about the next generation of boobies? Probability that a booby sperm or egg carries W = 0.8 or 80% Probability that a sperm or egg carries w = 0.2 or 20%

Copyright 2009 Pearson Education, Inc. Gametes reflect allele frequencies of parental gene pool W egg p = 0.8 Eggs w egg q = 0.2

Sperm W sperm w sperm p = 0.8 q = 0.8 WW Ww p2 = 0.64 pq = 0.16

wW qp = 0.16 ww q2 = 0.04 Next generation: Genotype frequencies 0.64 WW Allele frequencies 0.32 Ww

0.8 W 0.04 ww 0.2 w 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving What is the probability of a booby chick with a homozygous dominant genotype

(WW)? What is the probability of a booby chick with a homozygous recessive genotype (ww)? What is the probability of a booby chick with a heterozygous genotype (Ww)? Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving

If a population is in Hardy-Weinberg equilibrium, allele and genotype frequencies will not change unless something acts to change the gene pool Copyright 2009 Pearson Education, Inc. 13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving For a population to remain in HardyWeinberg equilibrium for a specific trait, it must satisfy five conditions:

1. Very large population 2. No gene flow between populations 3. No mutations 4. Random mating 5. No natural selection Copyright 2009 Pearson Education, Inc. 13.10 CONNECTION: The Hardy-Weinberg equation is useful in public health science Public health scientists use the HardyWeinberg equation to estimate frequencies

of disease-causing alleles in the human population One out of 3,300 Caucasian newborns in the United States have cystic fibrosis This disease, which causes digestive and respiratory problems, is caused by a recessive allele Copyright 2009 Pearson Education, Inc. 13.10 CONNECTION: The Hardy-Weinberg

equation is useful in public health science The frequency of individuals with this disease is approximately q2 = 1/3300 = 0.0003 The frequency of the recessive allele is q = .0174 or 1.7% The frequency of heterozygous carriers of cystic fibrosis is 2pq = 2 x 0.983 x 0.017 = 0.034 Around 3.4% of Caucasian Americans are

carriers for cystic fibrosis Copyright 2009 Pearson Education, Inc. MECHANISMS OF MICROEVOLUTION Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

If the five conditions for the HardyWeinberg equilibrium are not met in a population, the populations gene pool may change Mutations are rare and random and have little effect on the gene pool If mating is nonrandom, allele frequencies wont change much (although genotype frequencies may)

Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population The three main causes of evolutionary change are Natural selection Genetic drift Gene flow

Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Natural selection If individuals differ in their survival and reproductive success, natural selection will

alter allele frequencies Consider the boobies: Would webbed or nonwebbed boobies be more successful at swimming and capturing fish? Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

Genetic drift Genetic drift is a change in the gene pool of a population due to chance In a small population, chance events may lead to the loss of genetic diversity Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a

population Genetic drift The bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced For example, the northern elephant seal was hunted to near extinction in the 1700s and 1800s A remnant population of fewer than 100 seals was discovered and protected; the current population

of 175,000 descended from those few seals and has virtually no genetic diversity Animation: Causes of Evolutionary Change Copyright 2009 Pearson Education, Inc. Original population Original population

Bottlenecking event Original population Bottlenecking event Surviving

population 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Genetic drift Genetic drift produces the founder effect when a few individuals colonize a new habitat The smaller the group, the more different the gene pool of the new population will be from the gene pool of the original population

Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Gene flow Gene flow is the movement of individuals or gametes/spores between populations and can alter allele frequencies in a population Copyright 2009 Pearson Education, Inc.

13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Four moose were taken from the Canadian mainland to Newfoundland in 1904. These two males and two females rapidly formed a large population of moose that now flourishes in Newfoundland. Which mechanism is most likely to have contributed to the genetic differences between the mainland and Newfoundland moose? Gene flow

Founder effect Novel mutations Copyright 2009 Pearson Education, Inc. 13.11 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population The fossil remains of pygmy (or dwarf) mammoths (1.5 m to 2 m tall) have been found on Santa Rosa and San Miguel Islands off the coast of California. This population of pygmy mammoths is descended from a population of

mammoths of normal size (4 m tall). Dwarfing is common in island populations and is not the result of chance events. What mechanism do you think best accounts for the decrease in mammoth size on these islands? Gene flow Genetic drift Natural selection Copyright 2009 Pearson Education, Inc. 13.12 Natural selection is the only mechanism that

consistently leads to adaptive evolution An individuals fitness is the contribution it makes to the gene pool of the next and subsequent generations The fittest individuals are those that pass on the most genes to the next generation Copyright 2009 Pearson Education, Inc. 13.13 Natural selection can alter variation in a population in three ways

Stabilizing selection favors intermediate phenotypes, acting against extreme phenotypes Stabilizing selection is very common, especially when environments are stable Copyright 2009 Pearson Education, Inc. Frequency of individuals

Original population Phenotypes (fur color) Original Evolved population population Stabilizing selection Directional selection

Disruptive selection 13.13 Natural selection can alter variation in a population in three ways Example of stabilizing selection In Swiss starlings, clutch size varies from 1 to 8; the average clutch size is 4 Researchers marked chicks from different clutch sizes and recaptured fledglings after 3 months Birds from clutches with 3, 4, or 5 birds had

higher recapture rates than birds from clutches of 1 or 2 or 6, 7, or 8 Copyright 2009 Pearson Education, Inc. 13.13 Natural selection can alter variation in a population in three ways Directional selection acts against individuals at one of the phenotypic extremes Directional selection is common during

periods of environmental change, or when a population migrates to a new and different habitat Copyright 2009 Pearson Education, Inc. 13.13 Natural selection can alter variation in a population in three ways Disruptive selection favors individuals at both extremes of the phenotypic range This form of selection may occur in patchy

habitats Copyright 2009 Pearson Education, Inc. 13.14 Sexual selection may lead to phenotypic differences between males and females In many animal species, males and females show distinctly different appearance, called sexual dimorphism Intrasexual competition involves competition for mates, usually by males

Copyright 2009 Pearson Education, Inc. 13.14 Sexual selection may lead to phenotypic differences between males and females In intersexual competition (or mate choice), individuals of one sex (usually females) are choosy in picking their mates, often selecting flashy or colorful mates Copyright 2009 Pearson Education, Inc.

13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria As a result, natural selection is favoring bacteria that are resistant to antibiotics Natural selection for antibiotic resistance is particularly strong in hospitals

Many hospital-acquired infections are resistant to a variety of antibiotics Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides Laboratory strains of D. melanogaster have

been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use) Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern Lab strains established in the 1930s have

no alleles for DDT resistance; in lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37% Copyright 2009 Pearson Education, Inc. Head Thorax Abdomen

0.5 mm Dorsal BODY AXES (a) Adult Anterior Left

Ventral Right Posterior 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern Some fruit flies evolved resistance to DDT in order to survivetrue or false?

Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern Fruit flies became more resistant to DDT over timetrue or false? Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The

evolution of antibiotic resistance in bacteria is a serious public health concern When DDT was widely used, fruit flies with DDT resistance had greater evolutionary fitness than fruit flies lacking DDT resistancetrue or false? Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria

is a serious public health concern Alleles for DDT resistance may have been present but rare prior to DDT usetrue or false? Copyright 2009 Pearson Education, Inc. 13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern Alleles for DDT resistance arose by

mutation during the period of DDT use because of selection for pesticide resistancetrue or false? Copyright 2009 Pearson Education, Inc. 13.16 Diploidy and balancing selection preserve genetic variation Why doesnt natural selection act to eliminate genetic variation in populations, retaining only the most favorable alleles?

Diploidy preserves variation by hiding recessive alleles A recessive allele is only subject to natural selection when it influences the phenotype in homozygous recessive individuals For example, cystic fibrosis Copyright 2009 Pearson Education, Inc. 13.16 Diploidy and balancing selection preserve genetic variation

Balancing selection maintains stable frequencies of two or more phenotypes in a population In heterozygote advantage, heterozygotes have greater reproductive success than homozygous For example, sickle-cell anemia Copyright 2009 Pearson Education, Inc. 13.16 Diploidy and balancing selection preserve

genetic variation In frequency-dependent selection, two different phenotypes are maintained in a population For example, Indonesian silverside fishes Some variations may be neutral, providing no apparent advantage or disadvantages For example, human variation in fingerprints Copyright 2009 Pearson Education, Inc.

Right-mouthed Frequency of left-mouthed individuals 1.0 Left-mouthed 0.5

0 198182 83 84 85 86 87 88 89 90 Sample year 13.17 Natural selection cannot fashion perfect organisms 1. Selection can only act on existing variation Natural selection cannot conjure up new beneficial alleles

2. Evolution is limited by historical constraints Birds arose as the forelimb of a small dinosaur evolved into a wing Copyright 2009 Pearson Education, Inc. Wing claw (like dinosaur) Long tail with many vertebrae

(like dinosaur) Teeth (like dinosaur) Feathers 13.17 Natural selection cannot fashion perfect organisms 3. Adaptations are often compromises 4. Chance, natural selection and the

environment interact Copyright 2009 Pearson Education, Inc. You should now be able to 1. Describe Darwins concept of natural selection 2. Describe two examples of natural selection known to occur in nature 3. Explain how the fossil record, biogeography, comparative anatomy, comparative embryology, and molecular biology support

evolution 4. Explain how mutation and sexual recombination produce genetic variation 5. Describe the five conditions required for a population to be in Hardy-Weinberg equilibrium Copyright 2009 Pearson Education, Inc. You should now be able to 6. Explain the significance of the HardyWeinberg equilibrium to natural populations and to public health science 7. Define genetic drift and gene flow

8. Explain why natural selection is the only mechanism that leads to adaptive evolution 9. Distinguish between stabilizing selection, directional selection, and disruptive selection, and describe an example of each Copyright 2009 Pearson Education, Inc. You should now be able to 10.Distinguish between intrasexual selection and intersexual selection

11.Describe how antibiotic resistance has evolved 12.Explain how genetic variation is maintained in populations Copyright 2009 Pearson Education, Inc.

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