EVOLUTION

Chapter 13Chapter 13

Section 1: Charles Darwin and his theories

Darwin’s Theory of Evolution

Evolution, or change over time, is the , or change over time, is the process by which modern organisms have process by which modern organisms have descended from ancient organisms. descended from ancient organisms.

A scientific A scientific theory is a well-supported is a well-supported testable explanation of phenomena that testable explanation of phenomena that have occurred in the natural world.have occurred in the natural world.

Voyage of the Beagle

Voyage of Beagle

Dates: Dates: February 12th, 1831February 12th, 1831 ShipShip: H.M.S. Beagle: H.M.S. Beagle Destination:Destination: Voyage around the world. Voyage around the world. Findings:Findings: evidence to propose a evidence to propose a

revolutionary hypothesis about how life revolutionary hypothesis about how life changes over time as a result of an changes over time as a result of an organisms environmental conditions.organisms environmental conditions.

Science Before Darwin’s Voyage Most people believed each species was a divine creation.Most people believed each species was a divine creation. Scientists were trying to explain the origin of fossils.Scientists were trying to explain the origin of fossils.

Some tried to explain it by altering traditional explanations.Some tried to explain it by altering traditional explanations. Others (including Darwin’s grandfather) proposed mechanisms to explain how Others (including Darwin’s grandfather) proposed mechanisms to explain how

living things change over time.living things change over time.

1809: French scientist Jean Baptiste Lamarck proposed a hypothesis for 1809: French scientist Jean Baptiste Lamarck proposed a hypothesis for how organisms change over generations.how organisms change over generations. He believed that over the lifetime of an individual, physical features increased He believed that over the lifetime of an individual, physical features increased

in size b/c of use or reduce in size b/c of disuse.in size b/c of use or reduce in size b/c of disuse. He also believed these changes were then passed on to offspring.He also believed these changes were then passed on to offspring.

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Science Before Darwin’s Voyage

This is now known to be incorrect, however This is now known to be incorrect, however he did correctly point out that the changes he did correctly point out that the changes that occur in species are due to the physical that occur in species are due to the physical conditions of life- this refers to an conditions of life- this refers to an organisms environmental conditions.organisms environmental conditions.

Darwin’s Observations During Darwin’s voyage on the During Darwin’s voyage on the BeagleBeagle, he found , he found

evidence that species were not unchanging.evidence that species were not unchanging. Darwin was reading a book that discussed how changes Darwin was reading a book that discussed how changes

in the Earth could occur over many years. in the Earth could occur over many years. While he was out, he started to notice evidence of this.While he was out, he started to notice evidence of this.

Fossils- he found fossils in South America of extinct Fossils- he found fossils in South America of extinct armadillos. These armadillos closely resembled, but armadillos. These armadillos closely resembled, but were not identical to the armadillos still living in the were not identical to the armadillos still living in the area.area.

Fossils

The Galapagos Islands Located 620 miles off the coast of Ecuador.Located 620 miles off the coast of Ecuador. He noticed that many plants/animals He noticed that many plants/animals

resembled those of the nearby coast of South resembled those of the nearby coast of South America.America.

Darwin hypothesized that the most simple Darwin hypothesized that the most simple reason for this was that these animals had reason for this was that these animals had migrated to the islands and then changed over migrated to the islands and then changed over time.time.

Eventually Darwin called this “descent with Eventually Darwin called this “descent with modification” – what we now refer to as modification” – what we now refer to as evolution.evolution.

Animals found in the Galapagos

Land TortoisesLand Tortoises

Darwin FinchesDarwin Finches

Blue-Footed BoobyBlue-Footed Booby

Marine IguanasMarine Iguanas

Animals

The Journey Home

When Darwin was 27, he returned When Darwin was 27, he returned home, but did not report his findings. home, but did not report his findings.

He continued to study his data, until He continued to study his data, until his confidence grew that he was correct his confidence grew that he was correct in his conclusions.in his conclusions.

His hypothesis:His hypothesis: Separate species may Separate species may have arose from an original ancestorhave arose from an original ancestor

Population Growth Thomas MalthusThomas Malthus-19th century -19th century

English economistEnglish economist If population grew (more babies born If population grew (more babies born

than die)than die) Insufficient living spaceInsufficient living space Food runs out (populations are Food runs out (populations are

able to increase faster than food able to increase faster than food supply increases).supply increases).

He proposed that human He proposed that human populations do not grow populations do not grow unchecked because of death unchecked because of death caused by disease, war, and caused by disease, war, and famine that slows population famine that slows population growth.growth.

Darwin applied this theory to animals.

Growth of Populations Population: Population: includes all of the individuals of a species that live includes all of the individuals of a species that live

in a specific geographical area AND can interbreed (breed with in a specific geographical area AND can interbreed (breed with one another).one another).

Evolution by Natural SelectionEvolution by Natural Selection Darwin realized that Mathus’ conclusions about human Darwin realized that Mathus’ conclusions about human

population growth applied to all species.population growth applied to all species. Every organism has the potential to produce many offspring Every organism has the potential to produce many offspring

during its life time.during its life time. But, not all of them will survive.But, not all of them will survive.

Natural Selection After gathering all of his information, Darwin made a After gathering all of his information, Darwin made a

conclusion: “individuals that have physical or behavioral conclusion: “individuals that have physical or behavioral traits that better suit their environment are more likely to traits that better suit their environment are more likely to survive and will reproduce more successfully than those survive and will reproduce more successfully than those that do not have such traits”. Darwin called this that do not have such traits”. Darwin called this natural natural selection.selection. Over time, the number of individuals that carry favorable Over time, the number of individuals that carry favorable

characteristics that are ALSO inherited will increase in a characteristics that are ALSO inherited will increase in a population. Therefore, the population will change. This population. Therefore, the population will change. This changes = evolutionchanges = evolution..

Publication of Origin of Species 1844 Darwin wrote down his 1844 Darwin wrote down his

ideas about evolution & ideas about evolution & natural selection, but didn’t natural selection, but didn’t publish his data due to the publish his data due to the controversy that other controversy that other scientist were facing scientist were facing concerning this topic- he concerning this topic- he wasn’t confident enough.wasn’t confident enough.

Finally, he wrote the book & Finally, he wrote the book & it was published in Nov 1859.it was published in Nov 1859.

Darwin’s theory of evolution by natural selection is supported by 4 major points.1) Inherited variation exist w/in the genes of every

population or species (the result of random mutation & translation errors).

2) In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation) and have more offspring (natural selection).

3) Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population.

4) There is overwhelming evidence from fossils & many other sources that living species evolved from organisms that are extinct.

Darwin’s Ideas Updated Change within populations:Change within populations:

Darwin’s Darwin’s main point main point was that in any population, the individuals was that in any population, the individuals that are best suited to survive & do well in their environment will that are best suited to survive & do well in their environment will produce the most offspring. So, the traits of those individuals will produce the most offspring. So, the traits of those individuals will become more common in each new generation.become more common in each new generation.

Now, we know that genes are responsible for inherited traits.Now, we know that genes are responsible for inherited traits. Natural selection causes the frequency of certain alleles in a Natural selection causes the frequency of certain alleles in a

population to increase or decrease over time. population to increase or decrease over time. Mutations & the recombination of alleles that occurs during Mutations & the recombination of alleles that occurs during

sexual reproduction provide for endless sources of new sexual reproduction provide for endless sources of new variation.variation.

Species Formation Because the environment differs from place to Because the environment differs from place to

place, populations of the same species living in place, populations of the same species living in different locations tend to evolve in different different locations tend to evolve in different directions.directions.

Reproductive IsolationReproductive Isolation is the condition in which is the condition in which two populations of the same species do not breed two populations of the same species do not breed with one another b/c of geographic separation, a with one another b/c of geographic separation, a difference in mating periods, or other barriers to difference in mating periods, or other barriers to reproduction.reproduction.

Reproduction IsolationAs two isolated populations of As two isolated populations of

the same species become more the same species become more different over time, they may different over time, they may eventually become unable to eventually become unable to breed with one another. breed with one another. Usually, when this happens, Usually, when this happens, the two populations are the two populations are subsequently considered to subsequently considered to have become two different have become two different species.species.

The Tempo of Evolution

Evolution is understood to be a gradual Evolution is understood to be a gradual process that occurs continuously. process that occurs continuously.

This is called This is called gradualismgradualism.. Some scientists believe that evolution of Some scientists believe that evolution of

some species may actually occur in short some species may actually occur in short spurts, followed by long periods of no spurts, followed by long periods of no change. This change is called punctuated change. This change is called punctuated equilibrium.equilibrium.

Natural Selection

Over time, natural Over time, natural selection results in selection results in changes in inherited changes in inherited characteristics of a characteristics of a population. These population. These changes increase a changes increase a species fitness in its species fitness in its environmentenvironment

Evidence of Evolution

The Fossil RecordThe Fossil Record

Geographic Distribution of Living ThingsGeographic Distribution of Living Things

Homologous Body StructuresHomologous Body Structures

Similarities in Early DevelopmentSimilarities in Early Development

Evidence of Evolution The Fossil RecordThe Fossil Record Geographic Geographic

Distribution of Distribution of Living Things-Living Things-similar similar environments have environments have similar types of similar types of organismsorganisms

Homologous Body Homologous Body StructuresStructures

Similarities in Early Similarities in Early DevelopmentDevelopment

Section 2: Evidence of Evolution Fossils: offer the most direct evidence that evolution Fossils: offer the most direct evidence that evolution

takes place.takes place. A preserved/mineralized remain or imprint of an A preserved/mineralized remain or imprint of an

organism that lived long ago.organism that lived long ago.Provide an actual record of Earth’s past life-forms. Provide an actual record of Earth’s past life-forms. Change over time can be seen in the fossil record.Change over time can be seen in the fossil record.

• ie. Fossilized species found in older rocks are ie. Fossilized species found in older rocks are different from those found in newer rocks.different from those found in newer rocks.

After observing the differences in fossils, Darwin predicted that After observing the differences in fossils, Darwin predicted that intermediate forms between groups of organisms would eventually be intermediate forms between groups of organisms would eventually be found.found. Some have been found.Some have been found. Some have not.Some have not.

These intermediate forms are called transitional fossils.These intermediate forms are called transitional fossils. Any fossil which gives us information about a transition from one Any fossil which gives us information about a transition from one

species to another.species to another.

Examples of transitional fossils

Darwin’s theory is almost universally accepted by scientists Darwin’s theory is almost universally accepted by scientists as the best available explanation for the biological diversity as the best available explanation for the biological diversity on Earth:on Earth: Based on supporting evidence, most scientists agree on Based on supporting evidence, most scientists agree on

these 3 points:these 3 points:The Earth is about 4.5 million years old.The Earth is about 4.5 million years old.Organisms have inhabited the Earth for most of its Organisms have inhabited the Earth for most of its

history.history.All organisms living today share common ancestry All organisms living today share common ancestry

with earlier, simpler life forms.with earlier, simpler life forms.

Problems with fossils Many species have lived in environments where fossils do not form.Many species have lived in environments where fossils do not form. The environments most likely to cause fossil formation are wet The environments most likely to cause fossil formation are wet

lowlands, slow-moving streams, lakes, shallow seas, and areas near lowlands, slow-moving streams, lakes, shallow seas, and areas near volcanoes that spew out volcanic ash.volcanoes that spew out volcanic ash.

The chances that organisms living in certain areas will die at just the The chances that organisms living in certain areas will die at just the right spot to be fossilized are low.right spot to be fossilized are low.

Even if this does happen, the chances are low that the dead body will Even if this does happen, the chances are low that the dead body will be buried in sediment before it decays and/or is eaten by scavengers.be buried in sediment before it decays and/or is eaten by scavengers.

Rate of decay varies among organisms (hard skeleton vs soft Rate of decay varies among organisms (hard skeleton vs soft skeleton).skeleton).

Studying fossils

Paleontologist: scientists who study fossils.Paleontologist: scientists who study fossils. They analyze the sediments around the fossils.They analyze the sediments around the fossils. They use radiometric dating of certain rocks and They use radiometric dating of certain rocks and

minerals to arrange fossils in order from oldest to minerals to arrange fossils in order from oldest to youngest.youngest.

This creates a visual pattern of evolution.This creates a visual pattern of evolution.

Anatomy & Development Studying the anatomy of different types of Studying the anatomy of different types of

organisms often reveals basic similarities in body organisms often reveals basic similarities in body structures even through the structures function may structures even through the structures function may differ between organisms.differ between organisms. Vestigial structuresVestigial structures Homologous structuresHomologous structures Embryonic developmentEmbryonic development

Homologous StructuresHomologous Structures-structures that -structures that have different mature forms in different have different mature forms in different organisms, but develop from the same organisms, but develop from the same embryonic tissue.embryonic tissue.

Vestigial organsVestigial organs-organs that serve -organs that serve no useful function in an organismno useful function in an organism

i.e.appendix, miniature legs, armsi.e.appendix, miniature legs, arms

Similarities in Early Development

Biological Molecules In order for biology to match up with the changes in fossils, then In order for biology to match up with the changes in fossils, then

changes in a gene’s nucleotide sequence should build up over time changes in a gene’s nucleotide sequence should build up over time also.also.

ProteinsProteins One idea is that if evolution has taken place and a species has One idea is that if evolution has taken place and a species has

descended from a recent common ancestor, then they should descended from a recent common ancestor, then they should have few amino acid differences in their proteins.have few amino acid differences in their proteins.

This has been supported in test with hemolglobin- the same This has been supported in test with hemolglobin- the same hemoglobin protein in several species was analyzed and found hemoglobin protein in several species was analyzed and found to have few amino acid differences. to have few amino acid differences.

DNA Sequences

This pattern is not true for all proteins. This pattern is not true for all proteins. Some change faster than others, so the Some change faster than others, so the relationship may not be seen, if it did exist.relationship may not be seen, if it did exist.

Section 3- Examples of Evolution Natural Selection at WorkNatural Selection at Work

In Darwin’s writings, he offered examples of how In Darwin’s writings, he offered examples of how natural selection could have shaped life on Earth.natural selection could have shaped life on Earth.

KEY POINT: The environment dictates the KEY POINT: The environment dictates the direction and amount of change. direction and amount of change. If the environment changes in the future, the set If the environment changes in the future, the set

of characteristics that most help an individual of characteristics that most help an individual reproduce successfully may also change.reproduce successfully may also change.

Factors in Natural Selection The process is driven by 4 important points that are true The process is driven by 4 important points that are true

for all real populations.for all real populations. All populations have genetic variationAll populations have genetic variation The environment presents challenges to successful The environment presents challenges to successful

reproduction.reproduction. Individuals tend to produce more offspring than the Individuals tend to produce more offspring than the

environment can support.environment can support. Individuals that are better able to cope with the Individuals that are better able to cope with the

challenges tend to leave more offspring than those who challenges tend to leave more offspring than those who aren’t.aren’t.

An example Evolution of antibiotic resistant diseases.Evolution of antibiotic resistant diseases.

The bacteria needs to survive to reproduce.The bacteria needs to survive to reproduce. Eventually, a mutation will occur in its genome Eventually, a mutation will occur in its genome

that will allow even one bacteria cell to fight off that will allow even one bacteria cell to fight off the antibiotics. As it reproduces, more antibiotic the antibiotics. As it reproduces, more antibiotic resistant cells are made and the antibiotic resistant cells are made and the antibiotic currently used becomes ineffective.currently used becomes ineffective.

Darwin’s Finches: different beaks utilized during Darwin’s Finches: different beaks utilized during food shortage.food shortage.

Formation of a new species Species formation occurs in stages.Species formation occurs in stages. Natural selection favors changes that increase Natural selection favors changes that increase

reproductive success. reproductive success. So, species are improved to “fit” into their So, species are improved to “fit” into their

environment (ie. Fitness).environment (ie. Fitness). Accumulation of differences between groups- Accumulation of differences between groups-

divergencedivergence.. Divergence leads to the formation of new species.Divergence leads to the formation of new species. Formation of new species- Formation of new species- speciation.speciation.

Forming subspecies In environments differ enough, then separate In environments differ enough, then separate

populations of the same species can become so populations of the same species can become so different that they become a new species.different that they become a new species.

Populations of the same species that differ Populations of the same species that differ genetically b/c of adaptations to different living genetically b/c of adaptations to different living conditions become conditions become subspecies.subspecies.

Once they are different enough, the subspecies may Once they are different enough, the subspecies may become a completely separate species.become a completely separate species. Due to reproductive barriers that form.Due to reproductive barriers that form.

Summary of Darwin’s Theory

Individuals in nature differ from one Individuals in nature differ from one anotheranother

Organisms in nature produce more Organisms in nature produce more offspring than can survive, and many of offspring than can survive, and many of those who do not survive do not reproduce.those who do not survive do not reproduce.

Summary of Darwin’s Theory

Because more organisms are produce than Because more organisms are produce than can survive, each species must struggle for can survive, each species must struggle for resourcesresources

Each organism is unique, each has Each organism is unique, each has advantages and disadvantages in the advantages and disadvantages in the struggle for existencestruggle for existence

Summary (cont.)

Individuals best suited for the environment Individuals best suited for the environment survive and reproduce most successfulsurvive and reproduce most successful

Species change over timeSpecies change over time

Summary (cont.)

Species alive today descended with modification Species alive today descended with modification from species that lived in the pastfrom species that lived in the past

All organisms on earth are united into a single All organisms on earth are united into a single family tree of life by common descentfamily tree of life by common descent