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EvolutionEvolutionBiology’s Unifying ThemeBiology’s Unifying Theme
““Nothing in Nothing in biology biology
makes sense makes sense EXCEPT in the EXCEPT in the
light of light of evolution.” evolution.” Theodosius Theodosius DobzhanskyDobzhansky
Evolution
Charles Darwin in later yearsCharles Darwin in later years
Introduction Introduction
• Change is routine in biology.Change is routine in biology.
• All life is united.All life is united.
• Modern biology is defined by life’s Modern biology is defined by life’s unity and diversity.unity and diversity.
• The history of life is The history of life is a saga of a restless a saga of a restless Earth billions of Earth billions of years oldyears old
– Fossils document Fossils document this historythis history
Figure 1.10
– Evolution is one of biology’s best Evolution is one of biology’s best demonstrated, most comprehensive, demonstrated, most comprehensive, and longest lasting theoriesand longest lasting theories
– Evolution is the unifying theme of Evolution is the unifying theme of biologybiology
Charles DarwinCharles Darwin
• On November 24, 1859, Charles On November 24, 1859, Charles Darwin published Darwin published On the Origin of On the Origin of Species by Means of Natural Species by Means of Natural SelectionSelection..
• It has two main points:It has two main points:1.1. Evidence that modern species descended Evidence that modern species descended
from ancestral species.from ancestral species.
2.2. Natural selection is the mechanism from Natural selection is the mechanism from descent with modification.descent with modification.
Evidence of EvolutionEvidence of Evolution
• Earth was formed about 4.6 billion Earth was formed about 4.6 billion years ago. years ago.
• 3.9 billion years ago, fossil evidence 3.9 billion years ago, fossil evidence leads scientists to believe that there leads scientists to believe that there was a major change in weather was a major change in weather patterns, causing massive rainstorms patterns, causing massive rainstorms and flooding.and flooding.– This is due to carbon dating.This is due to carbon dating.– It is thought that the Earth was too hot to It is thought that the Earth was too hot to
support life until this point. No evidence support life until this point. No evidence of any living organism found in fossils.of any living organism found in fossils.
What are Fossils?What are Fossils?
• Preserved remnants or impressions Preserved remnants or impressions left by organism that lived in the left by organism that lived in the past.past.
• Fossils give some idea of the Earth’s Fossils give some idea of the Earth’s history.history.
• Most fossils are found in sedimentary Most fossils are found in sedimentary rock.rock.
Fossils (con’t)Fossils (con’t)
• Rock is divided into rock layers, and Rock is divided into rock layers, and each layers has a unique set of each layers has a unique set of fossils representing it.fossils representing it.
• Younger rock is layered on top of Younger rock is layered on top of older rock.older rock.
• The fossil record refers to the The fossil record refers to the ordered way in which fossils appear ordered way in which fossils appear in the rock layers, representing the in the rock layers, representing the passing of geological time.passing of geological time.
Fossils (con’t)Fossils (con’t)
• The oldest fossils date back to 3.5 The oldest fossils date back to 3.5 billion years ago.billion years ago.
• They are prokaryotic bacteria.They are prokaryotic bacteria.
Fossils (con’t)Fossils (con’t)
• Fossils have been found in the Fossils have been found in the following layers, giving scientists following layers, giving scientists an idea of the appearance of an idea of the appearance of various animals:various animals:(oldest (oldest youngest) youngest)– Fishlike fossilsFishlike fossils– AmphibiansAmphibians– ReptilesReptiles– MammalsMammals– BirdsBirds
Types of FossilsTypes of Fossils
CastsCasts
• Replica of an Replica of an organismorganism
AmberAmber
• Preserved and Preserved and frozen fossilsfrozen fossils
PetrifiedPetrified
• Stone copyStone copy
MoldsMolds
• Empty space in Empty space in rockrock
• Life evolvesLife evolves– Each species is one twig of a branching Each species is one twig of a branching
tree of life extending back in timetree of life extending back in time
Figure 1.11
Giantpanda
Spectacledbear
Slothbear Sun
bear
Americanblack bear
Asiaticblack bear
Polarbear Brown bear
Ancestral bear
Evolution: Evolution: genetic adaptation genetic adaptation of a population of organisms to of a population of organisms to
their environment over timetheir environment over timeMicroevolutionMicroevolution: Small-scale : Small-scale
changes in gene frequencies within changes in gene frequencies within a population.a population.
MacroevolutionMacroevolution: Large-scale : Large-scale evolutionary change resulting in evolutionary change resulting in new species and higher taxa new species and higher taxa (genera, families, etc.) and the (genera, families, etc.) and the extinction of species.extinction of species.
History of History of Evolutionary Evolutionary ThoughtThought
Early Ideas On Earth’s Early Ideas On Earth’s OrganismsOrganisms• AristotleAristotle
believed believed species were species were fixed creationsfixed creations arranged by arranged by their their complexitycomplexity
• Idea Idea lasted lasted 20002000 years years
Early Ideas On Earth’s Early Ideas On Earth’s OrganismsOrganisms• LinnaeusLinnaeus – 1 – 1stst to to
group similar group similar organisms and organisms and assign them assign them LatinLatin namesnames
• Two word name Two word name (Genus species)(Genus species)
• Known as Known as Binomial Binomial nomenclaturenomenclature
:
Contributor’s to Darwin’s Contributor’s to Darwin’s thinking included:thinking included:
•Charles Lyell –Charles Lyell –uniformatarianismuniformatarianism
•Georges Cuvier – Georges Cuvier – species species extinction (Catastrophism)extinction (Catastrophism)
•Thomas Malthus – Thomas Malthus – struggle struggle for existence (resources)for existence (resources)
:
Contributor’s to Darwin’s Contributor’s to Darwin’s thinking included:thinking included:
•James Hutton - James Hutton - GradualismGradualism•John Baptiste Lamarck – John Baptiste Lamarck –
Inheritance of acquired Inheritance of acquired CharacteristicsCharacteristics andand Law of Law of Use and DisuseUse and Disuse
•Alfred Russel Wallace – Alfred Russel Wallace – organisms evolved from organisms evolved from common ancestorscommon ancestors
Evolutionary TimelineEvolutionary Timeline
CatastrophismCatastrophism
•Idea proposed by Idea proposed by George George CuvierCuvier
•Studied fossil in Studied fossil in sedimentary sedimentary rock stratarock strata of Paris of Paris
•Found Found some species some species completely disappearedcompletely disappeared in in more recent layersmore recent layers
CatastrophismCatastrophism
• Stated that Stated that species species disappear due disappear due to a to a catastrophic catastrophic event of the event of the earth’s crustearth’s crust (volcano, (volcano, earthquake…)earthquake…)
Hutton’s Theory of Hutton’s Theory of Geological ChangeGeological Change
•James HuttonJames Hutton, 1795, Scottish , 1795, Scottish geologistgeologist•Studied Studied invertebrate fossils in invertebrate fossils in Paris MuseumParis Museum•Described The Described The Geological ForcesGeological Forces That Have Changed That Have Changed LifeLife on Earthon Earth Over Millions of Years (erosion, Over Millions of Years (erosion, earthquakes, volcanoes…)earthquakes, volcanoes…)
Hutton’s Theory of Hutton’s Theory of Geological ChangeGeological Change
•Changes in Changes in Earth’s crust Earth’s crust due to due to slow slow continuous continuous processesprocesses
• Idea Known as Idea Known as
GradualismGradualism
Charles LyellCharles Lyell• Proposed theory of Proposed theory of
UniformitarianismUniformitarianism• Geological Geological
processes at processes at uniform ratesuniform rates building & wearing building & wearing down Earth’s crustdown Earth’s crust
• Proposed that the Proposed that the Earth was millions Earth was millions of years instead of a of years instead of a few thousand years few thousand years oldold
Principles of GeologyPrinciples of Geology
• Published by Published by LyellLyell Just Before The Just Before The BeagleBeagle Set Sail & read by Darwin Set Sail & read by Darwin
• Explained Explained Geological Processes Geological Processes That Shaped The EarthThat Shaped The Earth
• Helped Darwin Understand Helped Darwin Understand Sea Sea Shells In The Andes Mountains At Shells In The Andes Mountains At 12,000+ Feet12,000+ Feet– Expanded Earth’s AgeExpanded Earth’s Age
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution• Jean-Baptiste LamarckJean-Baptiste Lamarck, ,
18091809• One Of First Scientists One Of First Scientists
To Understand That To Understand That Change Occurs Over Change Occurs Over TimeTime
• Stated that Changes Are Stated that Changes Are Adaptations To Adaptations To Environment Environment acquired in acquired in an organism’s lifetimean organism’s lifetime
• Said acquired changes Said acquired changes were passed to offspringwere passed to offspring
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution• Idea called Idea called
Law of Use Law of Use and Disuseand Disuse
• If a body part If a body part were used, it were used, it got strongergot stronger
• If body part If body part NOT used, it NOT used, it deteriorateddeteriorated
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution• Inheritance of Acquired Inheritance of Acquired
CharacteristicsCharacteristics• Proposed That By Selective Use Or Proposed That By Selective Use Or
Disuse Of Organs, Organisms Disuse Of Organs, Organisms Acquired Or Lost Certain Traits Acquired Or Lost Certain Traits During Their LifetimeDuring Their Lifetime
• These These Traits Could Then Be Passed Traits Could Then Be Passed On To Their OffspringOn To Their Offspring
• Over Time This Led To Over Time This Led To New SpeciesNew Species
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution• Use & Disuse - Use & Disuse -
Organisms Could Organisms Could Change The Size Or Change The Size Or Shape Of Organs By Shape Of Organs By Using Them Or Not Using Them Or Not Using ThemUsing Them
• Blacksmiths & Their Blacksmiths & Their SonsSons (muscular arms) (muscular arms)
• Giraffe’s Necks Giraffe’s Necks LongerLonger from from stretching)stretching)
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution
• Inheritance Of Acquired TraitsInheritance Of Acquired Traits– Traits Acquired During Ones Traits Acquired During Ones
Lifetime Would Be Passed To Lifetime Would Be Passed To OffspringOffspring
Clipped ears of dogs could be passed to offspring!
Lamarck’s Theory of Lamarck’s Theory of EvolutionEvolution• Tendency Toward PerfectionTendency Toward Perfection
• Organisms Are Continually Organisms Are Continually Changing and Acquiring Features Changing and Acquiring Features That Help Them Live More That Help Them Live More Successfully In Their EnvironmentSuccessfully In Their Environment
• Example:Example: Bird Ancestors Desired Bird Ancestors Desired To Fly So They Tried Until Wings To Fly So They Tried Until Wings DevelopedDeveloped
Lamarck’s MistakesLamarck’s Mistakes
•Lamarck Did NOT Know how Lamarck Did NOT Know how traits were traits were inherited (Traits inherited (Traits are passed through genes)are passed through genes)
•Genes Are NOT Changed By Genes Are NOT Changed By Activities In LifeActivities In Life
•Change Through Change Through Mutation Mutation Occurs Before An Organism Is Occurs Before An Organism Is BornBorn
Charles Darwin Charles Darwin the Naturalistthe Naturalist
Voyage of the BeagleVoyage of the BeagleCharles DarwinCharles Darwin• Born Feb. 12, 1809Born Feb. 12, 1809
• Joined Crew of HMS Joined Crew of HMS Beagle, 1831Beagle, 1831
• NaturalistNaturalist
• 5 Year Voyage 5 Year Voyage around worldaround world
• Avid Collector of Avid Collector of Flora & FaunaFlora & Fauna
• Astounded By Astounded By Variety of LifeVariety of Life
A reconstruction of the HMS Beagle sailing off Patagonia.A reconstruction of the HMS Beagle sailing off Patagonia.
Darwin’s Voyage of Darwin’s Voyage of DiscoveryDiscovery
Darwin Left England in Darwin Left England in 18311831
Darwin returned 5 years later in 1836Darwin returned 5 years later in 1836
HMS Beagle’s VoyageHMS Beagle’s Voyage
The Galapagos IslandsThe Galapagos Islands
• Small Group of Islands 1000 km Small Group of Islands 1000 km West of South AmericaWest of South America
•Very Different ClimatesVery Different Climates
•Animals On Islands UniqueAnimals On Islands Unique•TortoisesTortoises
•IguanasIguanas
•FinchesFinches
The Galapagos Islands are 600 miles off of Ecuador, on the equator.
The Galapagos IslandsThe Galapagos Islands• Volcanic islandsVolcanic islands off off
the coast of South the coast of South AmericaAmerica
• Island species Island species varied from varied from mainland species & mainland species & from island-to-from island-to-island speciesisland species
• Each island had Each island had long or short neck long or short neck tortoisestortoises
Galapagos Tortoise14 varieties10 survive
Galapagos Tortoise from island with tree cacti
Galapagos marine iguana evolved from land iguana. Found only on the Galapagos islands, different islands host different races.
Galapagos land iguanas
Galapagos PenguinSurvives because of large fish and crustacean populations fed by the nutrient-rich upwellings of the cold Humbolt current
The Galapagos IslandsThe Galapagos Islands
• Finches on the islands Finches on the islands resembled a resembled a mainland finchmainland finch
• More types of finches appeared on More types of finches appeared on the islandsthe islands where the available food where the available food was different (seeds, nuts, berries, was different (seeds, nuts, berries, insects…)insects…)
• Finches had Finches had different types of beaksdifferent types of beaks adapted to their adapted to their type of food type of food gatheringgathering
Darwin’s Finches
• FourteenFourteenspecies of species of Galápagos Galápagos finches finches have beak have beak shapes shapes adapted to adapted to suit their suit their environmeenvironmentnt
The beaks of the new species are adapted to exploit a different food source.
The tools to open nuts, catch insects, probe for grubs, etc. are all different.
• The evolutionary The evolutionary view of life came view of life came into focus in into focus in 1859 when 1859 when Charles Darwin Charles Darwin published published The The Origin of SpeciesOrigin of Species
• No mention of No mention of human evolutionhuman evolution
• Little mention of Little mention of origin of life, origin of life, focused on focused on “descent with “descent with modification”modification”
The Darwinian View of LifeThe Darwinian View of Life
Figure 1.12
• Darwin was struck by the diversity of Darwin was struck by the diversity of animals on the Galápagos Islandsanimals on the Galápagos Islands
Natural SelectionNatural Selection
• He thought of adaptation to the He thought of adaptation to the environment and the origin of new environment and the origin of new species as closely related processesspecies as closely related processes– As populations separated by a geographic As populations separated by a geographic
barrier adapted to local environments, barrier adapted to local environments, they became separate speciesthey became separate species
Survival of the FittestSurvival of the Fittest
Organisms that “fit” their environment the best are favored and go on to produce viable offspring.
Natural SelectionNatural Selection
• The basic idea of natural selection The basic idea of natural selection is:is:
1.1. That a population of organisms can That a population of organisms can change over generations.change over generations.
2.2. However, this only happens when However, this only happens when individuals having certain heritable individuals having certain heritable traits leave more offspring than other traits leave more offspring than other individuals.individuals.
Essentials of Natural Essentials of Natural SelectionSelection
1.1. Organisms produce far more Organisms produce far more offspring than can surviveoffspring than can survive
2.2. Competition for resourcesCompetition for resources
3.3. Individuals vary within a speciesIndividuals vary within a species
4.4. Those variants with better adapted Those variants with better adapted traits survive and reproduce, passing traits survive and reproduce, passing on those traits to the next on those traits to the next generation. generation.
Evolutionary Evolutionary AdaptationsAdaptations
A population increases in the A population increases in the frequency of traits that are frequency of traits that are suited to the environment. suited to the environment.
Result of natural selection.Result of natural selection.
Natural Selection BasicsNatural Selection Basics
• All species tend to produce excessive All species tend to produce excessive numbers offspring.numbers offspring.– The chances of the parents genetics The chances of the parents genetics
surviving increases.surviving increases.– However, the production of more However, the production of more
individuals can lead to a struggle for individuals can lead to a struggle for resources and life in a population; resources and life in a population; therefore, only a small percentage will therefore, only a small percentage will survive.survive.
• Individual variation is evident in Individual variation is evident in almost all species and most is almost all species and most is inherited.inherited.– All offspring of a particular species All offspring of a particular species
will not be identical.will not be identical.
Darwin’s Conclusions about Darwin’s Conclusions about Natural SectionNatural Section
• Individual’s whose inherited traits are Individual’s whose inherited traits are best suited to the local environment best suited to the local environment are likely to survive and reproduce.are likely to survive and reproduce.
• Eventually, the best traits will Eventually, the best traits will accumulate in the population over accumulate in the population over time and generations.time and generations.
Only the strong survive!!!Only the strong survive!!!
Darwin and GeneticsDarwin and Genetics
• Modern Synthesis – the joining of genetics Modern Synthesis – the joining of genetics with evolutionary biologywith evolutionary biology
• Darwin couldn’t explain the heredity Darwin couldn’t explain the heredity process of evolution.process of evolution.
• At the same time he was completing his At the same time he was completing his studies, Mendel was working on studies, Mendel was working on inheritance.inheritance.
• Mendel’s work explains the process Mendel’s work explains the process needed for natural selection to work.needed for natural selection to work.
Population EvolutionPopulation Evolution
• Populations – group of individuals of Populations – group of individuals of the same species living in the same the same species living in the same area at the same time.area at the same time.
• Populations is the smallest biological Populations is the smallest biological unit that can evolve.unit that can evolve.
• Evolution can only be tracked by how Evolution can only be tracked by how a population changes over time.a population changes over time.
Immigration leads to new Immigration leads to new variationvariation
• Immigration Immigration provides new provides new genetic material genetic material for selection to act for selection to act uponupon
Population GeneticsPopulation Genetics
Field of study that emphasizes the Field of study that emphasizes the extensive genetic variation within extensive genetic variation within populations and tracks the genetic populations and tracks the genetic makeup of populations over time.makeup of populations over time.
MicroevolutionMicroevolution
Microevolution – the generation-to-Microevolution – the generation-to-generation change in a population’s generation change in a population’s frequencies of alleles.frequencies of alleles.
3 Causes of Microevolution 3 Causes of Microevolution are:are:1.1. Genetic DriftGenetic Drift
- - Change in the gene pool of a small population Change in the gene pool of a small population due to chancedue to chance
2.2. Bottleneck EffectBottleneck Effect- Genetic drift due to a drastic reduction in Genetic drift due to a drastic reduction in
population sizepopulation size
3.3. Founder EffectFounder Effect- Cause of genetic drift when a few individuals Cause of genetic drift when a few individuals
colonize an island, lake, or other isolate habitatcolonize an island, lake, or other isolate habitat
Other factors in evolutionOther factors in evolution
• If there is no relation between fitness If there is no relation between fitness and the character in question, then and the character in question, then natural selection is not acting on itnatural selection is not acting on it
• Chance events can still make these Chance events can still make these traits show change over time = traits show change over time = RANDOM DRIFTRANDOM DRIFT
Chance events influence Chance events influence evolutionevolution
Not all populations are Not all populations are evolving.evolving.
Populations that do not evolve Populations that do not evolve are said to be in Hardy-are said to be in Hardy-Weinberg equilibrium.Weinberg equilibrium.
Darwinian FitnessDarwinian Fitness
• Darwinian Fitness – the contribution Darwinian Fitness – the contribution an individual makes to the gene pool an individual makes to the gene pool of the next generation relative to the of the next generation relative to the contribution of other individuals.contribution of other individuals.– Who has the best features and passed Who has the best features and passed
on the most is the most “fit.”on the most is the most “fit.”
Natural Selection OutcomesNatural Selection Outcomes
1.1. Directional selection – causes a Directional selection – causes a change in appearance of a populationchange in appearance of a population
2.2. Diversifying selection – leads to a Diversifying selection – leads to a balance between two of more varieties balance between two of more varieties in a populationin a population
3.3. Stabilizing selection – allows some Stabilizing selection – allows some variation for a a trait, but only within a variation for a a trait, but only within a narrow range (most prevalent) narrow range (most prevalent)
SummarySummary
• Natural Selection acts on whatever variation Natural Selection acts on whatever variation is present at the time. This variation is is present at the time. This variation is generated randomly with respect to generated randomly with respect to selection pressuresselection pressures
• Selection can be directional, stabilizing or Selection can be directional, stabilizing or disruptivedisruptive
• Random factors can also play a part in Random factors can also play a part in evolutionevolution
