Evolution and Biodiversity:

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Chapter 5

• Evolution and Biodiversity
• Origins, Niches, and Adaptation

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The 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

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Most widely-accepted hypothesis

• Organic molecules needed for life came from
  inorganic chemicals in the Earths atmosphere
• -energy from lightning
• -heat from volcanoes
• -intense UV light
• -other forms of solar radiation

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Scientific 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

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H2O
Electrode
CH4
CO2
Water vapor
N2
H2
NH3
Electrical sparks simulating lighting provide
energy to synthesize organic compounds
Condenser
Cold water
Cooled water containing organic compounds
H2O
Sample for chemical analysis
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Are there other possibilities?

• Organic molecules formed from
• Dust particles in space that reached earth on
  meteorites or comets
• Deep within the earth
• Hydrothermal vents (cracks in ocean floor, lead
  to chambers of molten rock)

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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

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Earth Developed in 2 Phases

• Chemical evolution organic molecules and
  chemical reactions to form protocells
• -1 billion years
• Biological Evolution single-celled prokaryotes ?
  single-celled eukaryotes ? multicellular
  organisms
• -3.8 billion years

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Chemical Evolution
Biological Evolution
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How do we know what organisms lived in the past?

• Fossils! mineralized or petrified replicas of
  skeletons, bones, teeth, shells, seeds, etc.
• Physical evidence of organisms
• Internal structures
• Fossil record is incomplete!
• We have 1 of species believed to have ever lived!

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What is Evolution?

• Evolution The change in a populations genetic
  makeup (gene pool) through successive generations
• Theory of Evolution all species developed from
  earlier, ancestral species

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Macro- 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

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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)

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Mutations

• Genetic variability originates through mutation
  random changes in the DNA in a cell.
• Mutations happen in two ways
• DNA is exposed to radioactivity, X-rays, mutagens
• Random mistakes when DNA is copied (cell
  division)
• ? Sometimes, mutations are beneficial

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Microevolution

• Microevolution change in a populations gene
  pool over time
• Summary of microevolution genes mutate,
  individuals are selected, populations evolve

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Natural Selection

• Occurs when individuals have traits that increase
  their chances of survival
• Needs 3 conditions
• Natural variability for a trait
• Trait must be heritable
• Must lead to differential reproduction
  (individuals with trait leave more offspring than
  individuals without trait)

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Lets think about the moths again

• Variability 2 color forms
• 2. Heritability color form was
  genetically-based
• 3. Differential reproduction greater survival
  and reproduction by one color

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When environment changes

• Population may
• Adapt to new conditions through natural selection
• Migrate to an area with better conditions
• 3. Become extinct

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3 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)

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Directional Natural Selection
Average
New average
Previous average
Snail coloration best adapted to conditions
Number of individuals
Number of individuals
Average shifts
Coloration of snails
Coloration of snails
Proportion of light-colored snails in population
increases
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Stabilizing Natural Selection
Dark snails eliminated
Light snails eliminated
Snails with extreme coloration are eliminated
Number of individuals
Number of individuals
Coloration of snails
Coloration of snails
Average remains the same, but the number of
individuals with intermediate coloration increases
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Diversifying Natural Selection
Snails with light and dark colors dominate
Intermediate-colored snails are selected against
Light coloration is favored
Dark coloration is favored
Number of individuals
Number of individuals
Coloration of snails
Coloration of snails
Number of individuals with light and dark
coloration increases, and the number with
intermediate coloration decreases
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Coevolution

• 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

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Ecological Niches

• Niche role of a species in an ecosystem (like an
  occupation)
• Habitat physical location (like an address)
• 2 types of niches
• Fundamental niche potential and theoretical
  niche (without competition, etc)
• Realized niche actual niche

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Niche separation
Generalist species with a broad niche
Number of individuals
Generalist species with a narrow niche
Niche breadth
Region of niche overlap
Resource use
Niche Overlap
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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

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120
120
80
80
80
80
40
120
120
135 million years ago
225 million years ago
EURASIA
AFRICA
120
80
0
120
40
120
120
INDIA
SOUTH AMERICA
65 million years ago
Present