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