Chapter 5Chapter 5

Evolution and Biodiversity:Evolution and Biodiversity:

Origins, Niches, and AdaptationOrigins, Niches, and Adaptation

The Origin of LifeThe Origin of Life

• How did life emerge on Earth?

• Chemical analysis and radioactive elements in rocks and fossils

• Simple inorganic compounds formed amino acids (proteins), simple sugars (carbs) and DNA/RNA

Most widely-accepted hypothesisMost widely-accepted hypothesis

• Organic molecules needed for life came from inorganic chemicals in the Earth’s atmosphere

-energy from lightning

-heat from volcanoes

-intense UV light

-other forms of solar radiation

Scientific ExperimentsScientific Experiments

• Since 1953

• Placed mixtures of gases (in early atmosphere) into closed containers

• Subjected gases to sparks (lightning) and heat

• Building blocks (necessary for life) formed

Electrical sparkssimulating lightingprovide energy tosynthesize organic compounds

Sample for chemical analysis

Cooled water containing organic compounds

Cold water

Condenser

Electrode

Water vapor

H2O

CH4

CO2N2

NH3 H2

H2O

Are there other possibilities?Are there other possibilities?

• Organic molecules formed from…

1. Dust particles in space that reached earth on meteorites or comets

2. Deep within the earth

3. Hydrothermal vents (cracks in ocean floor, lead to chambers of molten rock)

REGARDLESS…REGARDLESS…

• Organic molecules accumulated and underwent chemical reactions for several hundred million years

• Led to formation of proteins, RNA, and other polymers that formed protocells

• Protocells could take up materials from environment, grow, and divide

Earth Developed in 2 PhasesEarth Developed in 2 Phases

1. Chemical evolution: organic molecules and chemical reactions to form protocells

-1 billion years

1. Biological Evolution: single-celled prokaryotes single-celled eukaryotes multicellular organisms

-3.8 billion years

Formationof the

earth’searly

crust andatmosphere

Small organic

moleculesform in

the seas

Large organic

moleculesform in

the seas

First protocells

form inthe seas

Single-cellprokaryotes

form inthe seas

Single-celleukaryotes

form inthe seas

Multicellularorganismsform, firstin the seas and lateron land

© 2004 Brooks/Cole – Thomson Learning

Chemical Evolution

Biological Evolution

How do we know what organisms How do we know what organisms lived in the past?lived in the past?

• Fossils!: mineralized or petrified replicas of skeletons, bones, teeth, shells, seeds, etc.

1. Physical evidence of organisms

2. Internal structures

Fossil record is incomplete!

We have 1% of species believed to have ever lived!

What is Evolution?What is Evolution?

• Evolution: The change in a population’s genetic makeup (gene pool) through successive generations

• Theory of Evolution: all species developed from earlier, ancestral species

Macro- and MicroevolutionMacro- and Microevolution

• Microevolution: small genetic changes that occur in a population

• Macroevolution: long-term, large-scale evolutionary changes through which…

1. new species are formed from ancestral species

2. other species are lost through extinction

Remember…Remember…

• Genetic information in chromosomes is contained in DNA

• Genes (on chromosomes) represent certain traits that may be passed to offspring

• Gene pool: set of all genes in individuals of a population

• Alleles: different forms of a gene(dominant or recessive)

MutationsMutations

• Genetic variability originates through mutation: random changes in the DNA in a cell.

• Mutations happen in two ways:1. DNA is exposed to radioactivity, X-rays,

mutagens2. Random mistakes when DNA is copied

(cell division) Sometimes, mutations are beneficial

MicroevolutionMicroevolution• Microevolution: change in a population’s gene

pool over time• Summary of microevolution: genes mutate,

individuals are selected, populations evolve

Natural SelectionNatural Selection

• Occurs when individuals have traits that increase their chances of survival

• Needs 3 conditions:

1. Natural variability for a trait

2. Trait must be heritable

3. Must lead to differential reproduction (individuals with trait leave more offspring than individuals without trait)

Let’s think about the moths again…Let’s think about the moths again…

1. Variability: 2 color forms

2. Heritability: color form was genetically-based

3. Differential reproduction: greater survival and reproduction by one color

When environment changes…When environment changes…

Population may:

1. Adapt to new conditions through natural selection

2. Migrate to an area with better conditions

3. Become extinct

3 Types of Natural Selection3 Types of Natural Selection

1. Directional: changing environmental conditions select individuals who are not the norm so that their type makes up more of the population (“it pays to be different”)

2. Stabilizing: gets rid of individuals on both extremes (“it pays to be average”)

3. Diversifying: favors individuals with uncommon traits and reduces average individuals (“it does not pay to be normal”)

Natural selection

New average Previous average

Num

ber

of in

divi

dual

s

Coloration of snails

Proportion of light-coloredsnails in population increases

Num

ber

of in

divi

dual

s

Snail colorationbest adaptedto conditions

Average

Coloration of snails

Average shifts

Directional Natural SelectionDirectional Natural Selection

Coloration of snails

Light snailseliminated

Dark snailseliminated

Num

ber

of in

divi

dual

s

Coloration of snails

Snails withextreme

coloration areeliminated

Num

ber

of in

divi

dual

s

Average remains the same,but the number of individuals withintermediate coloration increases

Natural selection

Stabilizing Natural SelectionStabilizing Natural Selection

Number of individuals with light and dark coloration

increases, and the number with intermediate coloration decreases

Coloration of snails

Num

ber

of in

divi

dual

s Snails with light and darkcolors dominate

Coloration of snails

Num

ber

of in

divi

dual

s

Light colorationis favored

Darkcolorationis favored

Intermediate-colored snails are selected against

Natural selection

Diversifying Natural SelectionDiversifying Natural Selection

CoevolutionCoevolution

• Changes in the gene pool of one species leads to changes in gene pool of the other

Example: plants evolve defenses (camouflage, thorns, poison) effective against herbivores

Herbivores evolve immunity against these traits

Ecological NichesEcological Niches

• Niche: role of a species in an ecosystem (like an occupation)

• Habitat: physical location (like an address)

2 types of niches:1. Fundamental niche: potential and

theoretical niche (without competition, etc)

2. Realized niche: actual niche

How do new species evolve?How do new species evolve?

• Speciation: two species arise from one

• Geographic isolation: groups of the same population become physically separated and undergo different evolution

Ex. mountain range, volcano, earthquake

Leads to reproductive isolation

Early foxpopulation

separates

Adapted to heatthrough lightweightfur and long ears, legs, and nose, Which give off more heat.

Adapted to coldthrough heavierfur, short ears,short legs, shortnose. White furmatches snowfor camouflage.

Gray Fox

Arctic Fox

Different environmentalconditions lead to evolutioninto two different species.

Southern population

Northern population

EURASIA

AFRICA

SOUTHAMERICA

INDIA

135 million years ago

Present65 million years ago

225 million years ago

120°80° 0°

120°120°

120°

80°80° 80°80°40°

40°120° 120°

120°

GONDWANALANDGONDWANALAND

120°

LAURASIALAURASIA

PA

NG

AE

A

PA

NG

AE

A

ANTARCTICAANTARCTICA

AUSTRALIAAUSTRALIA

NORTH AMERICANORTH AMERICA

MADA-GASCARMADA-

GASCAR