Chapter 15: Macroevolution
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Transcript of Chapter 15: Macroevolution
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Chapter 15: Macroevolution
Origin of life
Big Bang
Early Earth
molton
atmosphere
1st this with water vapor and volcanic gasses
as earth cooled, H2O condensed, N2 escaped
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First fossils
3.5 billion years ago
stromatolite
can not be first life because they photosynthesized
Life is therefore older than 3.9 billion years
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How did life begin?
Current hypothesis
1. Abiotic synthesis of organic molecules
2. Small molecules join to form macromolecules
3. Macromolecules get packaged in membrane
4. Origin of self replicating molecule
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Evidence
Miller-Urey experiment
1923
tested hypothesis of JBS Haldane and AI Oparin
H2O, H2, CH4, NH3, + sparks = aas
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The path to life…
Polymers
produced by dehydration reactions and without enzymes
Protobionts
formed spontaneously in lab
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RNA World
Chicken vs Egg:
DNA-----RNA-----Protein
How did it evolve?
RNA that could self replicate (w/out ribosomes or proteins)
Ribozymes
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Once self replication exists, natural selection can begin
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Significant Events
Origin of single celled organisms
Origin of multi-celled organisms
Colonization of land
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Single Celled Organisms
Prokaryotes
Earth’s sole inhabitants from 3.5 to 3 bya
Transformed the atmosphere
O2 causeddecline in anaerobesincrease in aerobic prokaryotes
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Single Celled Organisms
Eukaryote
oldest fossil 2.1 bya
photosynthetic and/or respiratory prokaryotes living in larger cell
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Multi-Celled Eukaryotes
Oldest fossils 1.2 bya
Molecular clock suggests 1.5 bya
More diverse fossils 600 mya
Cambrian Explosion 535 to 525 mya
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Colonization of land by multi-celled eukarotes
500 mya
Plants and fungi colonized together
Arthropods and Tetrapods are the most widespread and diverse
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Human lineage diverged 6 to 7 mya
Homo sapiens diverged 195,000 ya
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How do we know?
Actual ages of rocks and fossilsradiometric dating
Fossil record documents history of life
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Radiometric Dating
Isotopes - use half life to determine age
C12/C14 good for young fossils (<25,000 years)
Other isotopes better for older fossils
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Fossil Record
Fossils appear in strata
Earth’s history divided into 3 Eons
Archaeon
Protozeroic
Phanerzoic
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Phanerzoic eon divided into 3 eras
Paleozoic
Mesozoic
Cenozoic
Boundaries of eras = mass extinctions
Lesser extinctions often mark boundaries of periods
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Cambrian Explosion
Suddenly all modern animal phyla appear
Why the sudden appearance?
1. Lots of empty niches
Or 2. Sudden appearance of hard body parts = good fossils
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Mechanisms of Macro Evolution
Continental Drift
Mass Extinctions
Adaptive Radiations
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Continental Drift
Proposed in 1916, accepted in 1960s
Since origin of eukaryotes, all continents have come together 3 times
1.1 bya
600 mya
250 mya
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Thin crust on hot mantle
Some places moving apartNorth America and Europe
Others moving together“Ring of Fire”
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Pangea
250 million years ago
Brought species together that had evolved separately
Inland seas drained
Interior of continenet probably extreme
Caused big biological shake up
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Break-up of Pangea
180 million years ago (mesozoic)
135 mya First split into north and south
65 mya modern continents take shapeend of mesozoic, beginning of cenozoic
55 mya India ran into Eurasia = Himalayas
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This pattern of continents merging and breaking up solves a lot of
puzzles
Marsupials vs eutharians
lungfishes
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Mass Extinctions
5 over past 500 million years
50% or more of earth’s species went extinct in each event
End of Permian and Cretaceous get most attention
End of Permian took 96% of marine animals
End of Cretaceous took >50% of marine species and dinosaurs
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Causes of mass extinctions
Permian
enormous volcanic eruptions in present day Serbia
lava, ash, CO2 increased T
slowed mixing of ocean between pole and equator = decrease in O2 in water
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Causes of mass extinctions
Cretaceous
Asteroid
iridium signature
65 my old crater off yucatan, 180 km in diameter
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Consequences of mass extinctions
Loss of whole ecosystems
Changes course of evolution
Recovery takes 5 to 10 million years or longer (100 my after permian)
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Is the 6th mass extinction underway?
> 1000 species have gone extinct in the last 400 years
100 to 1000 times normal rate
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Adaptive Radiations
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Evo-devo
Evolutionary changes caused by:
Changes in timing or rate of devolpment
Changes in spatial patterning
New genes/changes in genes
Changes in regulation
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How novelties can arrise
Gradual change
e.g. eyes
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Exaption
adapted for one purpose,
adopted for another
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Evolution is not goal oriented!
Trends don’t mean there is a goal.
Evolution is the result of existing organisms’ genetic diversity and the CURRENT
environment.
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Phylogenies
The evolutionary history of a species or group of species.
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Phylogenies
Inferred from
fossil record
morphological homologies
molecular homologies
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Analogous vs homologous structures
Convergent evolution can be misleading.
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Ocotillo found in SW US Alluaudia found in Madagascar
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Systematics
Focuses on classifying organisms and determines their evolutionary origin
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Taxonomists name things
Genus species
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Linneaus’s system still used:
SpeciesGenusFamilyOrderClass
PhylumKingdomDomains
africanaLoxodonta
ElephantidaeProboscideaMammaliaChordataAnimalia
Eukaryote
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Problems with the system…
It is all subjective and ultimately, arbitrary.
Phylocode
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Since Darwin, systematics
has expanded to reflect
evolutionary relationships in phylogenetic
trees.
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Constructing Trees
Cladistics
evolution proceeds when a new heritable trait developes
Shared derived characteristics
Shared ancestral characteristics
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Ingroup compared to outgroup
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Parsimony
the simplest hypothesis is most likely to be the correct one.
construct trees with fewest changes
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Trees as hypotheses
Best tree is only most likely
Always changing with new information
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Trees allow us to make and test predictions
The more we know the more accurately we can make and test predictions.
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Molecular Systematics
Comparing nucleic acids or other molecules to infer relatedness
Booming field - tons of new data
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Molecular Systematics
Can compare recent and ancient divergences
rDNA for ancient
mtDNA for recent
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Genome Evolution
Humans have 99% homology to mice
50% homology to yeast
Many shared biochemical and developemental pathways
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Overwhelming support for Darwin’s concept of
“decent with modification”
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Gene duplication
We can trace evolution of gene families
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The number of genes does not increase at the same rate as
organismal complexity.
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Molecular Clock
Some genomic regions appear to accumulate change at a constant rate.
Calibrated by graphing nucleotide changes vs date of branch
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Molecular systematics is helping link all life.
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A highly resolved Tree Of Life, based on completely sequenced genomes [1].
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