Download EOC Rev Day 6

Unit VI - Evolution
The Story of Life on Earth
Introduction to Evolution
• What does biological “evolution” mean?
– Change in a population of organisms over time
• How does this relate to the “origin of life”?
– It doesn’t…two different topics!
– Much more evidence to support evolution
– Remember: science deals with natural world,
not belief
Introduction to Evolution
• How could “life” have started?
– Old Idea:
• “spontaneous generation”
(abiogenesis)…nonliving matter makes living
• Disproved by Redi and Pasteur
– New Idea:
• “biogenesis”…life comes from life
Introduction to Evolution
• So, then where did the first cells come from?
– Early earth
• Very hot; volcanoes; violent storms/lightning
– Miller & Urey experiment
• Under early earth conditions, organic
compounds form & group together into
“protocells”
Introduction to Evolution
• But, when did we actually get cells? And how?
– Evidence of first cells
• 3.4 bln yrs ago
• Most likely anaerobic bacteria (no O2 in air)
– First photosynthetic cells
• 2.8 bln yrs ago
• Increased O2 in atmosphere
• Led to ozone layer that protects from UV rays =
more cells
• cells could make ATP better with aerobic
respiration
Evolutionary Theory
• Charles Darwin (1809-1882)
– “father” of evolutionary theory
– 1831 spent 5 years on HMS Beagle
– Visited the Galapagos Islands were he made
observations that would inspire his work
– 1859 published “On the Origin of Species by
means of Natural Selection”
Darwin’s Big Idea
Natural Selection/Survival of the Fittest
• Organisms
best
suited
for
their
environment are more likely to survive and
reproduce, passing on the characteristics
which helped them survive to their
offspring. Gradually leading to change in
the population over time.
Darwin’s Idea
• How did Darwin form ideas about evolution?
– Fossils showed organisms changed over time
Darwin’s Idea
• How did Darwin form ideas about evolution?
– Geologists showed that earth was very old
Darwin’s Idea
• How did Darwin form ideas about evolution?
– Malthus noticed populations grow faster than their
food supplies (they produce too many offspring)
Darwin’s Idea
• How did Darwin form ideas about evolution?
– Artificial selection (breeding) has brought about
many changes or modifications to species
Darwin’s Idea
• How did Darwin form ideas about evolution?
– He saw diverse species (ex: finches on Galapagos
Islands, all with variations isolated on each island)
Darwin’s Ideas
• What did Darwin
conclude about
populations?
– He identified that
populations change due
to “natural selection”
(nature selects who
goes on)
Darwin’s Ideas
• What did Darwin conclude about populations?
– Four assumptions:
• Populations produce large #’s of offspring (more
than can survive with given food)
• Individuals in population have variations
• Certain variations are more useful (these will
survive better)
• Over time, “good” genes prevail in the
population, while “bad” ones fade out
Evidence for Evolution
• What direct evidence supports this theory?
– Changes in populations over time
• Ex: peppered moth & MRSA
Evidence for Evolution
• What direct evidence supports this theory?
– Structural adaptations
• Ex: camouflage
Evidence for Evolution
• What direct evidence supports this theory?
– Structural adaptations
• Ex: mimicry
Evidence for Evolution
• What direct evidence
supports this theory?
– Physiological changes
• Ex: drug-resistant
bacteria; MRSA
• Ex: pesticide-resistant
insects
Evidence for Evolution
• Is there indirect evidence of evolution?
– Fossils
• show changes through time
Evidence for Evolution
• Is there indirect evidence of evolution?
– Anatomy
Evidence for Evolution
• Is there indirect evidence of evolution?
– Anatomy
• Homologous structures
– Similar origin, but may now have different function
– Shows common ancestry
– Ex: bird wing, whale flipper, human arm
Evidence for Evolution
• Is there indirect evidence of evolution?
– Anatomy
• Analogous structures
– Similar function, but very different structure
– Shows separate development…not related
– Ex: bird wing & butterfly wing
Evidence for Evolution
• Is there indirect evidence of evolution?
– Anatomy
• Vestigial structures
– A part that no longer serves a purpose
– Ex: snake hip bones; human wisdom teeth
Evidence for Evolution
• Is there indirect evidence of evolution?
– Embryology
• Early similarities may show relation
Evidence for Evolution
• Is there indirect evidence of evolution?
– Embryology
• Early similarities may show relation
Evidence for Evolution
• Is there indirect evidence of evolution?
– Embryology
Evidence for Evolution
• Is there indirect evidence of evolution?
– Biochemistry
• Similar chemicals in most life forms (DNA, ATP)
• More similarities in genetic code means closer
relationship
Mechanisms of Evolution
• Can individuals evolve?
– No!!!
– An organism is born with the only genes it will
ever have. These cannot be changed in that
individual.
– Only populations can evolve.
– This occurs when there are changes in the gene
frequencies (in the population)
– Gene pool = sum of all genes in population
Mechanisms of Evolution
• How do populations evolve?
– Any factor that affects genes in gene pool may
disrupt equilibrium…leads to change (evolution)
– Mutations may cause a shift (due to chance).
– Genetic drift may cause changes…especially in
small isolated populations.
– Gene flow – immigration/emigration into or out of
population
– Large populations not as affected by these
factors
Modes of Selection
Stabilizing Selection
• Pushes to average
• Ex: cactus with few
spines eaten by
animals more; cactus
with too many spines
invaded by more
parasites
Diversifying Selection
Pushes toward both extremes
Ex: small beak for soft seeds; large beak for hard seeds;
medium beak is bad at both types of seeds so selected
against
Directional Selection
Pushes toward ONE extreme or the other
Ex: in dry years, beak size pushed to larger
Mechanisms of Evolution
• How do species evolve?
– Called “speciation” - the development of a new
species (members of same species can breed)
For speciation to occur…there are a few things that
have to happen…
Geographic isolation
• keeps individuals apart so cannot
interbreed…over time they develop different
traits (Ex: finches on islands)
Mechanisms of Evolution
• How do species evolve?
– Called “speciation” (same species can breed)
– Geographic isolation
Mechanisms of Evolution
• How do species evolve?
After geographic isolation …
– Reproductive isolation
• no longer capable of interbreeding (timing,
parts, gametes differ,…)
Mechanisms of Evolution
• How fast can species evolve?
– Gradualism
• Speciation occurs over long periods of time
with gradual changes (takes millions of years)
– Punctuated equilibrium
• Speciation occurs in quick bursts with
equilibrium in between (~10,000 years or less)
Mechanisms of Evolution
• How fast can species evolve?
Mechanisms of Evolution
• Does evolution show patterns?
– Divergent evolution
• Ancestral species evolves into many species
that fit different habitats
• Ex: finches; common on islands
Mechanisms of Evolution
• Does evolution show patterns?
– Convergent evolution
• Distantly related organisms end up with similar
traits
• Occurs when have similar habitats
• Ex: cactus in N. American & euphorbias in
African deserts
Mechanisms of Evolution
• Does evolution show patterns?
– Convergent evolution
The End
Quiz – Evolution
for use with Questions 1 & 2
Quiz – Evolution
for use with Questions 3-5
Quiz – Evolution
for use with Question 6
Quiz – Evolution
for use with Question 7