Download Evolution - George Mason University

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Evolution
Bio 103 Lecture
Dr. Largen
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4Evidence of evolution
4Darwin’s theory and the modern synthesis
4Variation and natural selection
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A sea voyage helped Darwin frame his theory of evolution
4 Ideas about evolution originated before Darwin
– Aristotle (mid-350’s BC)
• natural similarities and relationships among organisms
• arranged organisms into “Scale of Nature”
– extended from most simple to most complex
• visualized organisms as imperfect but “moving toward a more perfect state”
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A sea voyage helped Darwin frame his theory of evolution
4 Ideas about evolution originated before Darwin
– “fossil”
• coined in early 1500s to describe remains of ancient organisms
– some corresponded to parts of familiar living organisms
– some were found in unexpected contexts
» marine invertebrates imbedded in rocks on high mountains
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A sea voyage helped Darwin frame his theory of evolution
4 Ideas about evolution originated before Darwin
– some fossils were unlike any any known form
– Leonardo da Vinci was the first to correctly interpret these finds
• as remains of animals that had existed in past but had become extinct
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A sea voyage helped Darwin frame his theory of evolution
4 Ideas about evolution originated before Darwin
– 1600s
• modern scientific thought emerged
– 1700s
• continental exploration expanded, new species discovered, more fossils found
• idea emerged that world of living organisms must be guided by natural laws
– similar to way physical world was governed by physical laws
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A sea voyage helped Darwin frame his theory of evolution
4 Ideas about evolution originated before Darwin
– 1809
• French naturalist Jean Baptiste de Lamarck, in Philosophie Zoologique, expressed most
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accepted view of evolution of the time
– organisms endowed with vital force that drives them to change toward greater
complexity over time
– organisms could pass traits acquired during their lifetimes on to their offspring
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Figure 22.x4 Jean Baptiste Lamarck
A sea voyage helped Darwin frame his theory of evolution
4 Darwin’s life and experiences
– led to development of his theory of evolution
• born in 1809
• father was a physician
• sent to University of Edinburgh to study medicine at age 15
– found himself unsuited for medicine
• transferred to Cambridge University to study theology and received his degree
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Figure 22.18 Charles Darwin in 1859, the year The Origin of Species was published
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A sea voyage helped Darwin frame his theory of evolution
4 Darwin’s life and experiences
– 1831 at age 22
• embarked on a 5-year round-the-world voyage as naturalist on H.M.S. Beagle
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• during voyage
– read extensively about geology
– collected 1000s of species of plants & animals, and fossils, including marine snail fossils
in the Andes
– observations on unique adaptations of organisms in South America
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A sea voyage helped Darwin frame his theory of evolution
4 Darwin returned to Great Britain at end of voyage in 1836
– readings and experiences had led him to seriously doubt current view that
• that Earth and living organisms were relatively new (having been specially created
only a few thousand years ago) and unchangeable
– came to believe that Earth was very old and constantly changing
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A sea voyage helped Darwin frame his theory of evolution
4 early 1840s
– Darwin composed essay describing major features of his theory
• knew his theory would cause a social furor so he delayed publishing it
4 meanwhile, in mid-1850s
– British naturalist named Alfred Wallace had been doing field work in Indonesia,
• conceived a theory identical to Darwin’s
4 1858
– Wallace’s work and excerpts from Darwin’s work were jointly presented to scientific community
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Figure 22.x5 Alfred Wallace
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A sea voyage helped Darwin frame his theory of evolution
4 1859
– Darwin’s text On the Origin of Species by Means of Natural Selection, was published
• didn’t use “evolution” at first
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– referred to “descent with modification”
• perceived a unity among species
– all organisms related through descent from unknown organisms that lived in the past
– as descendants spread into various habitats over millions of years
» accumulated adaptations
» adapted to various environments
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Figure 22.0 Title page from The Origin of Species
A sea voyage helped Darwin frame his theory of evolution
4 Darwin’s
phrase for evolution
– descent with modification
• captured the idea that
– an ancestral species could diversify into many descendant species
» by accumulation of different adaptations to various environments
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Figure 22.1 The historical context of Darwin’s life and ideas
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The study of fossils provide strong evidence for evolution
4 fossil record
– an ordered array in which fossils appear within layers, or strata, of sedimentary rack
• each strata can bear a unique set of fossils
– representing local sample of organisms that lived when sediment was deposited
• younger strata are on top of older strata
– thus, position of fossils in strata reveals relative age
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Figure 22.3 Formation of sedimentary rock and deposition of fossils from different time periods
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Figure 22.4 Strata of sedimentary rock at the Grand Canyon
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The study of fossils provide strong evidence for evolution
4 fossil record
– shows that organisms have appeared in a historical sequence
– oldest known fossils
• prokaryotes dating from ~ 3.5 billion years ago
– fossils in younger layers of rock
• reveal evolution of various groups of eukaryotes
– including successive appearance of various classes of vertebrates
» fishlike, then amphibians, then reptiles, then mammals and birds
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Figure 22.2 Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago
A mass of evidence validates the evolutionary view of life
4 Evidence that reinforces the fossil evidence for evolution
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biogeography
comparative anatomy
comparative embryology
molecular biology
A mass of evidence validates the evolutionary view of life
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biogeography
– geographical distribution of species
– is what first suggested to Darwin that organisms evolve from common ancestors
• although environment of Galapagos islands resembled that of tropical islands from
distant parts of world
– animals more closely resembled species of mainland South America than species on
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environmentally similar but distant islands
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Figure 22.16 The evolution of fruit fly ( Drosophila) species on the Hawaiian archipelago
A mass of evidence validates the evolutionary view of life
4 Comparative anatomy
– comparison of body structures in different species
– anatomical similarities among many species give sign of common descent
• same skeletal elements make up forelimbs of humans, cats, whales & bats
– since forelimbs of these animals function differently, would expect designs to be different,
unless
» they all descended from a common ancestor with same basic limb structure
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A mass of evidence validates the evolutionary view of life
4 Comparative anatomy
– homologous structures
• features that have different functions but are structurally similar because of common ancestry
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Figure 22.14 Homologous structures: anatomical signs of descent with modification
Figure 22.17 A transitional fossil linking past and present
A mass of evidence validates the evolutionary view of life
4 Comparative embryology
– study of structures that appear during development of different organisms
• closely related organisms often have similar stages in their embryonic development
– one sign that vertebrates evolved from a common ancestor
» all have embryonic stage in which structures called gill pouches appear on sides of throat
» at that stage, embryos of fishes, frogs, snakes, birds, apes look more alike than different
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A mass of evidence validates the evolutionary view of life
4 Molecular biology
– study of molecular basis of genes and gene expression
• universality of genetic code is strong evidence that all life is related
– related individuals have greater similarity in their DNA than do unrelated individuals of
same species
– two species judged to be closely related have a greater proportion of their DNA in
common than more distantly related species
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Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates
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Evolution of Populations
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Darwin proposed natural selection as the mechanisms of evolution
4 In The Origin of Species
Darwin focused on
– how organisms become adapted to their environments
– his theory arose from several key observations
• all species tend to produce more offspring than the environment can support
• individuals of a population vary in their traits
• organisms’ variations can be inherited by their offspring
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Darwin proposed natural selection as the mechanisms of evolution
4 all species tend to produce excessive numbers of offspring (overproduction )
– production of more individuals than an environment can support leads to a struggle
for existence
• natural resources are limited
• only a percentage of offspring in each generation survive and reproduce
– rest are starved, eaten, frozen, diseased, unmated, unable to reproduce for
some other reason
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Darwin proposed natural selection as the mechanisms of evolution
4 Individuals of a population vary extensively in their characteristics
– individuals whose characteristics make them best suited (adapted) to their environment
• most likely to survive
– most likely to reproduce
» leave more offspring than less “fit” (adapted) individuals
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Darwin proposed natural selection as the mechanisms of evolution
4 Many traits of individuals in population can be passed to next (heritable variations)
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• traits that made them well adapted to their environment are likely to be inherited by
their offspring
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Darwin proposed natural selection as the mechanisms of evolution
4 Darwin proposed that basic mechanism of evolution was natural selection
– essence of which is differential, or unequal, success in reproduction
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– traits of well adapted individuals will be more heavily represented in next generation
than traits of poorly adapted individuals
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Darwin proposed natural selection as the mechanisms of evolution
4 natural selection
– individuals that are well adapted to their environment
• are most fit for that environment, or “fittest”
– hence phrase “survival of the fittest”
– leads to, in subsequent generations,
• favored traits (well adapted) being represented more and more
• unfavored traits (poorly adapted) being represented less and less
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Darwin proposed natural selection as the mechanisms of evolution
4 natural selection
– unequal ability of individuals to survive and reproduce leads to
• gradual change in characteristics of a population of organisms
– favored characteristics accumulating
– unfavored characteristics disappearing over generations
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Darwin proposed natural selection as the mechanisms of evolution
4 artificial
selection
– selective breeding of domesticated plants and animals
– by selecting individuals with desired traits as breeding stock
• humans played role of environment and bringing about differential reproduction
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Darwin proposed natural selection as the mechanisms of evolution
4 artificial selection examples
– in plants
• all varieties of single species of wild mustard
» produced by artificial selection
– in animals
• hundreds of varieties of domestic dog, a single species called Canis familiaris,
– from 1000s of years of artificial selection
• many species of canines resulted from 1000s to millions of years of natural selection
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Figure 22.11b Artificial selection: diverse vegetables derived from wild mustard
Figure 22.11a Artificial selection: cattle breeders of ancient Africa
Darwin proposed natural selection as the mechanisms of evolution
4 if artificial selection could bring about so much change in relatively short time period
– natural selection over vast spans of time
• results in gradual accumulation of hertitable changes that would result in the evolution of
new species
– as in five species of canines thought to have evolved from a single ancestral canine
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Natural selection is a prominent force in nature
4 examples of natural selection ”in action”
– example, peppered moth
• exists in two forms
– light colored with splotches of darker pigment
– uniformly dark variety
• feed at night, rest during the day, on trees & rocks encrusted with lichens
– light variety is well-camouflaged against the lichens
– dark variety is conspicuous, therefore not protected from predators
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Natural selection is a prominent force in nature
4 peppered moth example, in Great Britain
– prior to the Industrial Revolution (in 19th century)
• dark variety of moth was rare
– was not camouflaged against lichens
» became prey for birds before they could reproduce and pass onto the next
generation their genes for dark coloration
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Natural selection is a prominent force in nature
4 peppered moth example, in Great Britain
– late 1800s, industrial pollution from Industrial Revolution killed large numbers of lichens,
exposing the darker tree bark or rock
• dark variety of moth became more abundant
– since it now was camouflaged against dark surface and lighter variety was not
• by early 1900s, populations of peppered moth consisted almost entirely of dark variety
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Populations are the units of evolution
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– group of individuals of same species living in same place at same time
– is smallest unit that can evolve
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• moth example, it was population, not individual moths, that evolved
– evolution can be measured as a change in prevalence of certain heritable traits in a population
over a succession of generations
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Populations are the units of evolution
4 Darwin could not explain
– cause of variation among individuals making up population
– perpetuation of parents’ traits in their offspring
4 Because of knowledge that came after Darwin, today we understand that
– mutations in genes may produce new traits
– heritable traits are carried by genes on chromosomes
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Populations are the units of evolution
4 modern synthesis
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theory of evolution that includes genetics, developed in early 1940s
focuses on populations as units of evolution
includes most of Darwin’s ideas
melds population genetics with the theory of natural selection
requires an understanding of relationship between populations and species
• sexual species (biological species)
– group of individuals w/ potential to interbreed & produce fertile offspring
Microevolution is change in a population’s gene pool over time
4 gene pool
– total collection of genes in a population at any one time
– is reservoir from which members of next generation of that population will derive their
genes
– can be studied by observing changes in relative frequencies of alleles over time
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Microevolution is change in a population’s gene pool over time
4 For most gene loci, there are 2 or more alleles
– population at a given time can be described by relative frequencies of a particular set of
alleles
– over time, relative frequencies of particular alleles in population can change as a result of
natural selection
• as in moth example
• such a change in gene pool is called microevolution
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The gene pool of an idealized, non-evolving population remains constant over the
generations
4 frequency of each allele in gene pool will remain constant unless acted on by other
agents
– population to which this applies is said to be in Hardy-Weinberg equilibrium
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Five conditions are required for Hardy-Weinberg equilibrium
4 Hardy-Weinberg equilibrium
– suggests that something other than sexual reproduction is required to alter a gene pool
• by changing allele frequencies from one generation to the next
4 One way to determine what factors can change a gene pool is to
– identify conditions necessary to maintain genetic equilibrium
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Figure 23.3a The Hardy-Weinberg theorem
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Figure 23.3b The Hardy-Weinberg theorem
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Five conditions are required for Hardy-Weinberg equilibrium
4 Hardy-Weinberg equilibrium
– can be maintained in nature only if 5 conditions met
– population is very large
– population is isolated
• no migration of individuals (and therefore their alleles) into or out of population
– gene mutations do not alter gene pool
– mating is random
– all individuals are equal in reproductive success
• natural selection does not occur
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Five conditions are required for Hardy-Weinberg equilibrium
4 five conditions necessary for Hardy-Weinberg equilibrium rarely occur in nature
– equilibrium breaks down
– allele frequencies in natural populations change constantly
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There are five potential causes of microevolution
4 Five agents of microevolution
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genetic drift
gene flow
mutation
nonrandom mating
natural selection
There are five potential causes of microevolution
4 Genetic drift
– change in gene pool of a small population due to chance
– if population is small, chance event can have a disproportionately large effect
• altering gene pool in next generation
– iguana example, assume small population (3 WW, 2 Ww and 5 ww)
» an earthquake kills 3 iguana
» 3 dead iguanas were all WW
» frequency of W allele in next generation would be reduced
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There are five potential causes of microevolution
4 Genetic drift, subtypes
– bottleneck effect
• results from event that drastically reduces population size
• as occurs when natural disaster kills large numbers of individuals unselectively
– small surviving population not likely to have same genetic makeup as original population
» after event, certain alleles present at higher frequencies, other alleles present at lower
frequencies
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There are five potential causes of microevolution
4 Genetic
drift, subtypes
– founder effect
• results from random change in gene pool that occurs in small colony
• colonization of new location by single pregnant individual or small # of individuals
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– gene pool of subsequent generations derived from these few individuals
• thought to have been important in evolution of many species in Galapagos Islands
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Figure 23.4 Genetic drift
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There are five potential causes of microevolution
4 Gene flow
– gain or loss of alleles from a population by movement of individuals or gametes
– occurs when fertile individuals move into or out of a population or gametes are transferred from one
population to another
– tends to reduce genetic differences between populations
– reproductive isolation reduces gene flow and increases genetic differences between populations
– migration and wars tend to increase gene flow among populations
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There are five potential causes of microevolution
4 Mutation
– random change in organism’s DNA, creates new allele
– mutations of a given gene is rare event
• occurs ~1X/ gene locus per 105 to 106 gametes
– in large population
• mutation alone has little effect in single generation
– over the long term
• mutation vital to evolution
– ultimate source of genetic variation
» serves as raw material for evolution
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There are five potential causes of microevolution
4 Nonrandom mating
– selection of mate other than by chance
– for Hardy-Weinberg equilibrium to be maintained
• every male in population must have equal chance of mating with every female in
population (random mating)
• rarely occurs
• nonrandom mating is norm in most populations
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There are five potential causes of microevolution
4 Natural selection
– fifth agent of microevolution
– differential success in reproduction
– most likely to result in adaptive changes in a gene pool
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Not all genetic variation may be subject to natural selection
4 Some genetic variation in populations seems to have trivial impact on reproductive success
– may not be subject to natural selection
4 neutral variation hypothesis
– proposes that species typically have numerous alleles that confer no selective advantage or
disadvantage
– frequencies of these alleles may increase or decrease as a result of chance genetic drift but natural
selection will not affect them
• human fingerprints are probably an example of neutral variation
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The perpetuation of genes defines evolutionary fitness
4 Evolutionary fitness
– contribution an individual makes to gene pool of next generation relative to contribution
made by other individuals
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– fittest individuals in an evolutionary context
• those that pass on greatest number of genes to next generation
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Natural selection acts on whole organisms and affects genotypes as a result
4 Individuals with high degree of fitness are those whose
– phenotypic traits enable them to reproduce and contribute genes to more offspring than
other individuals
4 Favored genotypes are are those whose
– positive phenotypic effects outweigh any harmful effects they may have on reproductive
success of organism
4 By culling less fit individuals
– natural selection culls unfavored genotypes
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There are three main modes of natural selection
4 natural
selection can alter phenotypic variations in an idealized population
– three main
• stabilizing selection
• directional selection
• diversifying selection
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There are three main modes of natural selection
4 Stabilizing selection
– favors intermediate variants
– typically occurs in relatively stable environments
• where conditions tend to reduce phenotypic variation
– probably prevails most of time in most populations
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There are three main modes of natural selection
4 Directional selection
– shifts overall makeup of population by acting against individuals at one of phenotypic
extremes
– most common
• during periods of environmental change
• when members of a species migrate to some new habitat with different
environmental conditions
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There are three main modes of natural selection
4 Diversifying selection
– typically occurs when environmental conditions are varied in way that favors
individuals at both extremes of a phenotypic range rather than intermediate
individuals
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Figure 23.12 Modes of selection
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Directional selection has produced resistant populations of pests and parasites
4 Natural selection has produced resistant populations of pests and parasites
– when a pesticide, antibiotic, drug is first used
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• fairly effective killing all but a few individuals in target population
• survivors live and reproduce because, by chance, they have genes that protect them
(provide resistance)
– survivors pass these protective traits on t\o their offspring
» eventually, most of population consists of resistant individuals
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Figure 22.12 Evolution of insecticide resistance in insect populations
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