Natural SelectionNatural Selection

I have called this principle, by whicheach slight variation, if useful, is preserved,

by the term Natural Selection.

  —Charles Darwin from "The Origin of Species"Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://evolution.berkeley.edu/evolibrary/home.php

http://evolution.berkeley.edu/evolibrary/home.php

www.darwinday.org/englishL/life/beagle.htUsed by permission of Darwin Day Celebration (at DarwinDay.org), 2006

www.darwinday.org/englishL/life/beagle.html

http://evolution.berkeley.edu/evolibrary/home.php

CHARLES DARWIN – 1809-CHARLES DARWIN – 1809-18821882

• EnglishEnglish• Traveled around the world on the Beagle Traveled around the world on the Beagle

(ship)(ship)• Most of trip was among the Galapagos IslandsMost of trip was among the Galapagos Islands• Believed that the earth was 6000 years old Believed that the earth was 6000 years old

and that all plants and animals were and that all plants and animals were unchangeable over timeunchangeable over time

• During his travels, he observed many live During his travels, he observed many live species, as well as fossils species, as well as fossils

• He did not understand why some species He did not understand why some species survived while others were going extinctsurvived while others were going extinct

• These ideas went directly against his beliefsThese ideas went directly against his beliefs

Darwin’s ObservationsDarwin’s Observations

• From island to island, he noticed that the From island to island, he noticed that the species of mockingbird, finches, and other species of mockingbird, finches, and other animals varied.animals varied.

• Many of the species Darwin collected had Many of the species Darwin collected had not yet been discovered or classifiednot yet been discovered or classified

• Darwin took his collections and drawings Darwin took his collections and drawings home and after reading essays and studies home and after reading essays and studies by many other scientists (Gould & Mathus), by many other scientists (Gould & Mathus), he developed the idea of natural selectionhe developed the idea of natural selection

5 Principles of Natural 5 Principles of Natural SelectionSelection

1.1. Individuals in a population show Individuals in a population show variation.variation.

2.2. Variations can be inherited.Variations can be inherited.

3.3. Organisms have more offspring that can Organisms have more offspring that can survive under normal circumstances.survive under normal circumstances.

4.4. Variations that increase reproductive Variations that increase reproductive success will have a greater chance of success will have a greater chance of being passed on from generation to being passed on from generation to generation.generation.

5.5. A population will slowly change over time A population will slowly change over time in response to the environment.in response to the environment.

Darwin…Darwin…• By 1840, Darwin had developed the theory By 1840, Darwin had developed the theory

of natural selection.of natural selection.• He then published “He then published “On the Origin of Species On the Origin of Species

by Means of Natural Selection”by Means of Natural Selection”• On the last page of this book, he called his On the last page of this book, he called his

theory “evolution”theory “evolution”– Evolution is what the process is called ~ Evolution is what the process is called ~

natural selection is HOW evolution happensnatural selection is HOW evolution happens

• Another researcher, Wallace, also wrote a Another researcher, Wallace, also wrote a similar book at the same time and both similar book at the same time and both books were published and presented to the books were published and presented to the scientific community.scientific community.

Evolution Overview:Evolution Overview:Evidence for Evolution, Evidence for Evolution,

Types of Natural Types of Natural Selection, & SpeciationSelection, & Speciation

Biology 1Biology 1

Dr. ButtsDr. Butts

How and why does evolution How and why does evolution occur?occur?• Individuals are born with random traits Individuals are born with random traits

inherited from parentsinherited from parents

• Some of these traits might be Some of these traits might be advantageousadvantageous

• Individuals who have more advantage Individuals who have more advantage in their environment will survive and in their environment will survive and reproduce with greater successreproduce with greater success

• The advantageous traits will be passed The advantageous traits will be passed down to offspringdown to offspring

Evidence of EvolutionEvidence of Evolution• The Fossil RecordThe Fossil Record

– Provides records of Provides records of species that lived species that lived long agolong ago

– Shows evolutionary Shows evolutionary relationships among relationships among ancient and current ancient and current living thingsliving things

Evidence of EvolutionEvidence of Evolution

Comparative Anatomy: Comparative Anatomy: – Homologous Structures: anatomically Homologous Structures: anatomically

similar structures that occur in species similar structures that occur in species that come from a common ancestorthat come from a common ancestor

Evidence of EvolutionEvidence of EvolutionComparative Comparative

AnatomyAnatomy– Vestigial Vestigial

Structures: Structures: structures that structures that are present, but are present, but no longer neededno longer needed

Evidence of EvolutionEvidence of EvolutionComparative Comparative

AnatomyAnatomy– Analogous Analogous

Structures: Structures: structures that structures that are similar in are similar in function, but function, but are not in living are not in living things that things that share ancestryshare ancestry

Evidence of EvolutionEvidence of EvolutionComparative Comparative

EmbryologyEmbryology– Studying of the Studying of the

growth and growth and development of development of various organismsvarious organisms

– The more similar The more similar the embryonic the embryonic development of development of organisms, the organisms, the more closely more closely related they arerelated they are

Evidence of EvolutionEvidence of Evolution

• Comparative Biochemistry: Comparative Biochemistry: comparing DNA and other moleculescomparing DNA and other molecules

• The more closely related, the more The more closely related, the more similar the DNA sequencessimilar the DNA sequences

Evidence of EvolutionEvidence of Evolution

• Geographic Geographic Distribution & Distribution & BiogeographyBiogeography

• Similar climates Similar climates and biomes have and biomes have similar living similar living things because things because living things evolve living things evolve to be successful in to be successful in their environmenttheir environment

CoEvolutionCoEvolution

Some species evolve in close Some species evolve in close relationship with other species. The relationship with other species. The relationship may sometimes become relationship may sometimes become so close that the evolution of one so close that the evolution of one species may affect the other.species may affect the other.

Examples of Evidence: CoevolutionExamples of Evidence: Coevolution

Examples of Evidence:Examples of Evidence:

•Camouflage: blending in with environment

•Mimicry: nonpoisonous organisms mimicking poisonous ones in order to avoid predators

CamouflageCamouflage

Mimicry Mimicry

Evidence of EvolutionEvidence of Evolution• Antibiotic Antibiotic and and

Pesticide Pesticide ResistanceResistance

• Antibiotic: Antibiotic: bacteria become bacteria become resistant to resistant to antibiotics over antibiotics over time due to over time due to over and misuseand misuse

• Pesticide: Insects Pesticide: Insects and other pests and other pests become resistant become resistant to pesticides due to pesticides due to overuseto overuse

Adaptation & Natural Adaptation & Natural SelectionSelection• Camouflage: Camouflage:

blending in with blending in with environmentenvironment

• Mimicry: Mimicry: nonpoisonous nonpoisonous organisms organisms mimicking mimicking poisonous ones in poisonous ones in order to avoid order to avoid predatorspredators

Adaptation & Natural Adaptation & Natural SelectionSelection• Genetic DriftGenetic Drift

– Founder Effect:Founder Effect: Pioneer species Pioneer species leaves original leaves original colony and begins colony and begins a new onea new one

– Bottleneck:Bottleneck: a once a once large population is large population is dramatically dramatically decreased due to decreased due to some bottleneck some bottleneck event (ex. event (ex. Drought, flood, Drought, flood, disease, etc)disease, etc)

Adaptation & Natural Adaptation & Natural SelectionSelection• Stabilizing Stabilizing

SelectionSelection• most commonmost common• eliminates eliminates

extremes, which extremes, which gets rid of negative gets rid of negative traitstraits

• ex. Birth weights of ex. Birth weights of human babies does human babies does not show variationnot show variation

Adaptation & Natural Adaptation & Natural SelectionSelection• Directional Directional

SelectionSelection

• one extreme one extreme selected forselected for

• ex. Peppered ex. Peppered moth (p.435, fig. moth (p.435, fig. 15.17)15.17)

Adaptation & Natural Adaptation & Natural SelectionSelection• Disruptive Disruptive

SelectionSelection

• splits a population splits a population into 2 groupsinto 2 groups

• removes average removes average individuals and individuals and selects for extremesselects for extremes

• Ex. Selection based Ex. Selection based on habitat (snakes in on habitat (snakes in grasslands vs. rocky grasslands vs. rocky mountains)mountains)

Adaptation & Natural Adaptation & Natural SelectionSelection• Sexual SelectionSexual Selection• mate selection mate selection

based on physical based on physical characteristicscharacteristics

• Nonrandom Nonrandom MatingMating

• mating based on mating based on nonrandom factors nonrandom factors (proximity, sexual (proximity, sexual selection, etc)selection, etc)

SpeciationSpeciation• What is a species?What is a species?• Groups of organisms Groups of organisms

that can successfully that can successfully reproduce with one-reproduce with one-another.another.

• What is speciation?What is speciation?• Process by which new Process by which new

species are formedspecies are formed• Populations diverge to Populations diverge to

the point they can no the point they can no longer reproduce longer reproduce together (together (reproductive reproductive isolationisolation))

SpeciationSpeciation

• Allopatric Allopatric SpeciationSpeciation

• Physical barrier Physical barrier causes speciationcauses speciation

• Sympatric Sympatric SpeciationSpeciation

• Speciation without Speciation without a physical barriera physical barrier

SpeciationSpeciation• Adaptive Adaptive RadiationRadiation

• Rapid evolution Rapid evolution due to due to environmental environmental factor(s) that factor(s) that cause a change cause a change in what is in what is advantageous advantageous vs. vs. disadvantageousdisadvantageous

SpeciationSpeciation• CoevolutionCoevolution• Species evolve Species evolve

in response to in response to one anotherone another

• Convergent Convergent EvolutionEvolution

• Similar traits Similar traits evolve in evolve in different parts of different parts of the world due to the world due to similar climates similar climates and geographyand geography

Hardy WeinbergHardy Weinberg• Theory that states that if gene Theory that states that if gene

frequencies remain stable, the frequencies remain stable, the population is said to be in equilibrium population is said to be in equilibrium (or homeostasis) and thus, not (or homeostasis) and thus, not evolving.evolving.

• 5 things must be true:5 things must be true:1. Population is large.1. Population is large.2. No immigration nor emigration2. No immigration nor emigration3. Mating is always random.3. Mating is always random.4. Mutations never occur4. Mutations never occur5. Natural selection does not occur.5. Natural selection does not occur.

Hardy WeinbergHardy Weinberg• Is it true for humans? You decide…Is it true for humans? You decide…• Assumes 5 things to be true:Assumes 5 things to be true:

1. Population is large?1. Population is large?2. No immigration nor emigration?2. No immigration nor emigration?3. Mating is always random?3. Mating is always random?4. Mutations never occur?4. Mutations never occur?5. Natural selection does not occur?5. Natural selection does not occur?

• Are populations ever really NOT Are populations ever really NOT evolving then?evolving then?