Chapter 15 Macroevolution Origin of life Big Bang
Chapter 15: Macroevolution Origin of life Big Bang Early Earth molton atmosphere 1 st 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 can not be first life because they photosynthesized Life is therefore older than 3. 9 billion years
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 H 2 O, H 2, CH 4, NH 3, + 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
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 O 2 caused decline in anaerobes increase 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 fossils radiometric dating Fossil record documents history of life
Radiometric Dating Isotopes - use half life to determine age C 12/C 14 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 1960 s Since origin of eukaryotes, all continents have come together 3 times 1. 1 bya 600 mya 250 mya
Thin crust on hot mantle Some places moving apart North 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 shape end 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, CO 2 increased T slowed mixing of ocean between pole and equator = decrease in O 2 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 6 th 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
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 Ocotillo found in SW US Alluaudia found in Madagascar Convergent evolution can be misleading.
Systematics Focuses on classifying organisms and determines their evolutionary origin
Taxonomists name things Genus species
Linneaus’s system still used: Species Genus Family Order Class Phylum Kingdom Domains africana Loxodonta Elephantidae Proboscidea Mammalia Chordata Animalia Eukaryote
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 r. DNA for ancient mt. DNA 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. A highly resolved Tree Of Life, based on completely sequenced genomes [1].
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