Evolution. What is evolution? Evolution is defined as “descent with modification” Evolution is defined as “descent with modification” – a.k.a. “Change.

EvolutionEvolution

What is evolution?What is evolution?• Evolution is defined as “descent with Evolution is defined as “descent with

modification”modification”– a.k.a. “Change over time”a.k.a. “Change over time”

Leaves on Leaves on trees trees

change change color and color and fall over fall over several several weeks. weeks.

Mountain Mountain ranges ranges

erode over erode over millions of millions of

years. years.

Over a large Over a large number of years, number of years,

evolution produces evolution produces tremendous tremendous

diversity in forms diversity in forms of life. of life.

Isn’t Evolution ‘just’ a Isn’t Evolution ‘just’ a theory?theory?

• Scientific theories are explanation that Scientific theories are explanation that are based on lines of evidence, enable are based on lines of evidence, enable valid predictions, and have been tested valid predictions, and have been tested in many ways.in many ways.

• In contrast, there is also a popular In contrast, there is also a popular definition of theory – a “guess” or definition of theory – a “guess” or “hunch”“hunch”

These conflicting definitions cause some These conflicting definitions cause some confusion when it comes to evolution… confusion when it comes to evolution…

Descent with Descent with modification???modification???

• We’ve defined evolution as descent with modification from We’ve defined evolution as descent with modification from a common ancestor, but exactly what has been modified? a common ancestor, but exactly what has been modified?

• Compare these two examples of change in beetle Compare these two examples of change in beetle populations. Which one is an example of evolution?populations. Which one is an example of evolution?– Beetles on a dietBeetles on a diet

• Imagine a year or two of drought in which there are few plants that Imagine a year or two of drought in which there are few plants that these beetles can eat. these beetles can eat.

• All the beetles have the same chances of survival and reproduction, All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles.little smaller than the preceding generation of beetles.

– Beetles of a different colorBeetles of a different color• Most of the beetles in the population (say 90%) have the genes for Most of the beetles in the population (say 90%) have the genes for

bright green coloration and a few of them (10%) have a gene that bright green coloration and a few of them (10%) have a gene that makes them more brown.makes them more brown.

• Some number of generations later, things have changed: brown Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% beetles are more common than they used to be and make up 70% of the population. of the population.

• Which example illustrates descent with modification—a Which example illustrates descent with modification—a change in gene frequency over time?change in gene frequency over time?

Who is Charles Who is Charles Darwin?Darwin?

• An English scientistAn English scientist• Considered the Considered the

“father of modern “father of modern evolutionary evolutionary theory”theory”

• Studies animal and Studies animal and plant life as a ship’s plant life as a ship’s naturalist. From naturalist. From these findings he these findings he was able to develop was able to develop his theory of his theory of evolutionevolution

The Galapagos IslandsThe Galapagos Islands• Aboard the H.M.S Beagle, Aboard the H.M.S Beagle,

Darwin traveled to the Darwin traveled to the Galapagos IslandsGalapagos Islands– The Galapagos supports a The Galapagos supports a

great deal of diversity in great deal of diversity in both plant and animal lifeboth plant and animal life

– Darwin studied & compared Darwin studied & compared the anatomy of many the anatomy of many species of:species of:• ReptilesReptiles• InsectsInsects• Birds**Birds**• Flowering plantsFlowering plants

All of which were unique to All of which were unique to the island, but similar to the island, but similar to species found around the species found around the worldworld

Darwin notices Darwin notices strugglesstruggles

• Competition for space & foodCompetition for space & food– Need to escape from predatorsNeed to escape from predators– Need to find enough preyNeed to find enough prey– Ability to find AND secure shelterAbility to find AND secure shelter– SURVIVAL OF THE FITTEST…SURVIVAL OF THE FITTEST…

What is Natural What is Natural Selection?Selection?

• Natural selection is one of the basic Natural selection is one of the basic mechanisms of evolution, along mechanisms of evolution, along with mutation, migration, and with mutation, migration, and genetic drift.genetic drift.

• Darwin’s grand idea of evolution by Darwin’s grand idea of evolution by natural selection is relatively simple natural selection is relatively simple but often misunderstood. but often misunderstood.

To find out how Natural To find out how Natural Selection works, imagine a Selection works, imagine a

population of beetles:population of beetles:• There is variation in traits. There is variation in traits. – For example, some beetles are For example, some beetles are

green and some are brown green and some are brown

• There is differential There is differential reproduction.reproduction.– Since the environment can’t Since the environment can’t

support unlimited population support unlimited population growth, not all individuals get growth, not all individuals get to reproduce to their full to reproduce to their full potential. In this example, potential. In this example, green beetles tend to get green beetles tend to get eaten by birds and survive to eaten by birds and survive to reproduce less often than reproduce less often than brown beetles do. brown beetles do.

• There is heredity.– The surviving brown beetles

have brown baby beetles because this trait has a genetic basis.

• End result:– The more advantageous trait,

brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

To find out how Natural Selection To find out how Natural Selection works, imagine a population of works, imagine a population of

beetles (continued…)beetles (continued…)

Natural Selection Natural Selection OverviewOverview

• In nature, there is a In nature, there is a tendency towards the tendency towards the overproduction of offspringoverproduction of offspring

• In any population of In any population of organisms, individuals will organisms, individuals will exhibit slight variationsexhibit slight variations– Individuals with variations that Individuals with variations that

are favorable for a particular are favorable for a particular environment are more likely to environment are more likely to survive and pass those survive and pass those variations on to the next variations on to the next generation than are individuals generation than are individuals with less-favorable variationswith less-favorable variations

– Gradually, offspring of Gradually, offspring of survivors will make up a larger survivors will make up a larger proportion of the population proportion of the population and eventually a population and eventually a population may look entirely differentmay look entirely different

What is fitness?What is fitness?• Biologists use the word Biologists use the word fitnessfitness to to

describe how good a particular describe how good a particular genotypegenotype is at leaving offspring in the is at leaving offspring in the next generation relative to how good next generation relative to how good other genotypes are at it.other genotypes are at it.

• Fitness is a relative thing. A Fitness is a relative thing. A genotype’s fitness depends on the genotype’s fitness depends on the environment in which the organism environment in which the organism lives. lives.

The brown beetles have a The brown beetles have a greater fitness relative to the greater fitness relative to the

green beetles.green beetles.

Fitness in NatureFitness in Nature

Caring for your offspring (A), and producing Caring for your offspring (A), and producing thousands of young — many of whom won't thousands of young — many of whom won't survive (above right), and sporting fancy survive (above right), and sporting fancy feathers that attract females (left) are a feathers that attract females (left) are a burden to the health and survival of the burden to the health and survival of the parent. These strategies do, however, parent. These strategies do, however, increase fitness because they help the increase fitness because they help the

parents get more of their offspring into the parents get more of their offspring into the next generation. next generation.

AA BB

CC

Mechanisms of Mechanisms of EvolutionEvolution

• MutationMutation– A mutation could cause parents A mutation could cause parents

with genes for bright green with genes for bright green coloration to have offspring with a coloration to have offspring with a gene for brown coloration. gene for brown coloration.

– That would make the genes for That would make the genes for brown beetles more frequent in brown beetles more frequent in the population. the population.

• MigrationMigration– Some individuals from a population Some individuals from a population

of brown beetles might have joined of brown beetles might have joined a population of green beetles. a population of green beetles.

– That would make the genes for That would make the genes for brown beetles more frequent in brown beetles more frequent in the green beetle population. the green beetle population.

• Genetic DriftGenetic Drift– Imagine that in one generation, two Imagine that in one generation, two

brown beetles happened to have brown beetles happened to have four offspring survive to reproduce. four offspring survive to reproduce.

• Several green beetles were killed Several green beetles were killed when someone stepped on them and when someone stepped on them and had no offspring. had no offspring.

• The next generation would have a The next generation would have a few more brown beetles than the few more brown beetles than the previous generation—but just by previous generation—but just by chance. chance.

• These chance changes from These chance changes from generation to generation are known generation to generation are known as genetic drift. as genetic drift.

• Natural SelectionNatural Selection– Imagine that green beetles are Imagine that green beetles are

easier for birds to spot (and hence, easier for birds to spot (and hence, eat). eat).

• Brown beetles are a little more likely Brown beetles are a little more likely to survive to produce offspring. to survive to produce offspring.

• They pass their genes for brown They pass their genes for brown coloration on to their offspring. coloration on to their offspring.

• So in the next generation, brown So in the next generation, brown beetles are more common than in beetles are more common than in the previous generation. the previous generation.

Mechanisms of Mechanisms of EvolutionEvolution

Evolution Mechanisms Evolution Mechanisms UnderstoodUnderstood

• Mutation…• Migration…• Genetic Drift…• Natural Selection…

– All of these mechanisms can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change.

– However, natural selection and genetic drift cannot operate unless there is genetic variation—that is, unless some individuals are genetically different from others. • If the population of beetles were 100% green,

selection and drift would not have any effect because their genetic make-up could not change.

Natural Selection & Natural Selection & AdaptationAdaptation

• AdaptationAdaptation– Any trait that aids the chances of Any trait that aids the chances of

survival and reproduction of an survival and reproduction of an organismorganism

– Can be explained by applying Can be explained by applying Darwin’s theory of natural selectionDarwin’s theory of natural selection

– We will focus on two types of We will focus on two types of adaptations:adaptations:•StructuralStructural

– Changes in the structure of body partsChanges in the structure of body parts

•PhysiologicalPhysiological– Changes in an organism’s metabolic Changes in an organism’s metabolic

processesprocesses

Structural AdaptationsStructural Adaptations• Can be used as

defense mechanisms– Mimicry

• A structural adaptation that provides protection for an organism by copying the appearance of another, more threatening, species

– Camouflage• A structural adaptation

that enables an organism to blend in with its surroundings

Non-Non-poisonous poisonous

king king snakes snakes mimic mimic

poisonous poisonous coral coral

snakes.snakes.Katydids Katydids have have

camouflagcamouflage to look e to look

like leaves.like leaves.

Physiological Physiological AdaptationsAdaptations• Anti-biotic implicationsAnti-biotic implications

– Individual bacteria in a population show Individual bacteria in a population show variationvariation

– Some bacteria possess a gene that makes them Some bacteria possess a gene that makes them resistant to some antibioticresistant to some antibiotic

– When the population is exposed to the antibiotic, When the population is exposed to the antibiotic, some individuals die, but resistant bacteria some individuals die, but resistant bacteria survivesurvive

– Resistant bacteria survive and reproduceResistant bacteria survive and reproduce– In time, the entire population is resistant to a In time, the entire population is resistant to a

certain antibioticcertain antibiotic

““Why does Evolution matter NOW?” Why does Evolution matter NOW?” http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1notes.html

““The Evolution of Antibiotic Resistance” The Evolution of Antibiotic Resistance” http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html

““Why does Evolution Why does Evolution matter NOW?” Video matter NOW?” Video

QuestionsQuestionshttp://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1notes.html

1.1. Why is the Russian prison system considered Why is the Russian prison system considered to be "ground zero" in the fight against TB? to be "ground zero" in the fight against TB?

2.2. What is responsible for the evolution of TB What is responsible for the evolution of TB strains that are resistant to multiple drugs? strains that are resistant to multiple drugs?

3.3. How does the misuse of antibiotics affect the How does the misuse of antibiotics affect the evolution of disease-causing bacteria? Use evolution of disease-causing bacteria? Use the theory of natural selection to explain the the theory of natural selection to explain the growing resistance to antibiotics. growing resistance to antibiotics.

4.4. Why should we care about a resistant strain Why should we care about a resistant strain of TB in Russia?of TB in Russia?

Evidence for EvolutionEvidence for Evolution• FossilsFossils can show evolutionary can show evolutionary

changes over timechanges over time

• Anatomical structureAnatomical structure indicate indicate evolutionary relationshipevolutionary relationship– Analogous structuresAnalogous structures show show

similaritysimilarity in structure based on in structure based on adaptation for the same adaptation for the same function, not common descent.function, not common descent.

• FunctionlessFunctionless structures structures indicate evolutionary indicate evolutionary pathwayspathways– Seemingly functionless parts Seemingly functionless parts

are called are called vestigial organs or vestigial organs or structuresstructures..

Evidence for EvolutionEvidence for Evolution

• Embryological development Embryological development shows evolution from a shows evolution from a common ancestorcommon ancestor– Structures that are Structures that are

embryologically similar,embryologically similar, but but have have different functions,different functions, are are called called homologous homologous structuresstructures..

• Genetic comparisonsGenetic comparisons may may reveal hidden relationships.reveal hidden relationships.

• Amino acid sequences are Amino acid sequences are similar in related similar in related organisms!organisms!

Jean Baptiste LamarckJean Baptiste Lamarck• FrenchFrench Biologist Biologist• Believed in Believed in SPONTANEOUS SPONTANEOUS

GENERATIONGENERATION• Believed that Believed that living things evolved living things evolved

in a continually upward direction, in a continually upward direction, from dead matter, through simple from dead matter, through simple to more complex forms, toward to more complex forms, toward perfectionperfection

• Believed that organisms Believed that organisms altered altered their behavior in response to an their behavior in response to an environmental change; these environmental change; these changes caused modification to changes caused modification to their organs & internal structure.their organs & internal structure. He further believed that these He further believed that these modifications were inherited by modifications were inherited by the organism’s offspringthe organism’s offspring

• Didn’t believe that species died Didn’t believe that species died out in extinctions, but instead they out in extinctions, but instead they changed into other specieschanged into other species