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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, H 2 O condensed, N 2 escaped. First fossils 3.5 billion years ago stromatolite - PowerPoint PPT Presentation
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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
Evidence
Miller-Urey experiment
1923
tested hypothesis of JBS Haldane and AI Oparin
H2O, H2, CH4, NH3, + sparks = aas
The path to life…
Polymers
produced by dehydration reactions and without enzymes
Protobionts
formed spontaneously in lab
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
Significant Events
Origin of single celled organisms
Origin of multi-celled organisms
Colonization of land
Single Celled Organisms
Prokaryotes
Earth’s sole inhabitants from 3.5 to 3 bya
Transformed the atmosphere
O2 causeddecline in anaerobesincrease in aerobic prokaryotes
Single Celled Organisms
Eukaryote
oldest fossil 2.1 bya
photosynthetic and/or respiratory prokaryotes living in larger cell
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
Colonization of land by multi-celled eukarotes
500 mya
Plants and fungi colonized together
Arthropods and Tetrapods are the most widespread and diverse
Human lineage diverged 6 to 7 mya
Homo sapiens diverged 195,000 ya
How do we know?
Actual ages of rocks and fossilsradiometric dating
Fossil record documents history of life
Radiometric Dating
Isotopes - use half life to determine age
C12/C14 good for young fossils (<25,000 years)
Other isotopes better for older fossils
Fossil Record
Fossils appear in strata
Earth’s history divided into 3 Eons
Archaeon
Protozeroic
Phanerzoic
Phanerzoic eon divided into 3 eras
Paleozoic
Mesozoic
Cenozoic
Boundaries of eras = mass extinctions
Lesser extinctions often mark boundaries of periods
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
Mechanisms of Macro Evolution
Continental Drift
Mass Extinctions
Adaptive Radiations
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”
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
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
This pattern of continents merging and breaking up solves a lot of
puzzles
Marsupials vs eutharians
lungfishes
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
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
Causes of mass extinctions
Cretaceous
Asteroid
iridium signature
65 my old crater off yucatan, 180 km in diameter
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)
Is the 6th mass extinction underway?
> 1000 species have gone extinct in the last 400 years
100 to 1000 times normal rate
Adaptive Radiations
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
How novelties can arrise
Gradual change
e.g. eyes
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.
Phylogenies
The evolutionary history of a species or group of species.
Phylogenies
Inferred from
fossil record
morphological homologies
molecular homologies
Analogous vs homologous structures
Convergent evolution can be misleading.
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Ocotillo found in SW US Alluaudia found in Madagascar
Systematics
Focuses on classifying organisms and determines their evolutionary origin
Taxonomists name things
Genus species
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
Since Darwin, systematics
has expanded to reflect
evolutionary relationships in phylogenetic
trees.
Constructing Trees
Cladistics
evolution proceeds when a new heritable trait developes
Shared derived characteristics
Shared ancestral characteristics
Ingroup compared to outgroup
Parsimony
the simplest hypothesis is most likely to be the correct one.
construct trees with fewest changes
Trees as hypotheses
Best tree is only most likely
Always changing with new information
Trees allow us to make and test predictions
The more we know the more accurately we can make and test predictions.
Molecular Systematics
Comparing nucleic acids or other molecules to infer relatedness
Booming field - tons of new data
Molecular Systematics
Can compare recent and ancient divergences
rDNA for ancient
mtDNA for recent
Genome Evolution
Humans have 99% homology to mice
50% homology to yeast
Many shared biochemical and developemental pathways
Overwhelming support for Darwin’s concept of
“decent with modification”
Gene duplication
We can trace evolution of gene families
The number of genes does not increase at the same rate as
organismal complexity.
Molecular Clock
Some genomic regions appear to accumulate change at a constant rate.
Calibrated by graphing nucleotide changes vs date of branch
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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