Transcript Unit 8 Evolution

Unit VI - Evolution
~ a unifying theme of biology ~
Introduction to Evolution
• What does biological “evolution” mean?
– Change in 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
• Aerobic cells could now develop
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?
– He saw diverse species (ex: finches on Galapagos
Islands, all with variations)
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 Ideas
• What did Darwin
conclude about
species?
– He identified that
populations change due
to “natural selection”
(nature selects who
goes on)
Darwin’s Ideas
• What did Darwin conclude about species?
– 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
Evidence for Evolution
• What direct evidence supports this theory?
– Structural adaptations
• Ex: mimicry; camouflage
Evidence for Evolution
• What direct evidence
supports this theory?
– Physiological changes
• Ex: drug-resistant
bacteria;
• 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?
– 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 code means closer
relationship
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
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
Mechanisms of Evolution
• Can individuals evolve?
– No!
– Genes are genes…cannot alter them*
– Only populations can evolve
– 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
– Smaller populations more affected…higher
chance to concentrate recessives
– Organisms moving in/out cause changes
– Large populations not as affected by these factors
Mechanisms of Evolution
• How do species evolve?
– Called “speciation” (same species can breed)
– 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?
– Called “speciation” (same species can breed)
– Reproductive isolation
• no longer capable of interbreeding (timing,
parts, gametes differ,…)
Mechanisms of Evolution
• How fast can species evolve?
– Gradualism
• Species start up over long time with gradual
changes (millions of years)
– Punctuated equilibrium
• Speciation occurs in quick bursts with
equilibrium in between (~10,000 yrs 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 S. American & African deserts
Mechanisms of Evolution
• Does evolution show patterns?
– Convergent evolution
Modes of Selection
Directional Selection
Pushes toward ONE extreme or the other
Ex: in dry years, beak size pushed to larger
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
Stabilizing Selection
• Pushes to average
• Ex: cactus with few
spines eaten by
animals more; cactus
with too many spines
invaded by more
parasites
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