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First year SBC174 Evolution course - week 2 1. NeoDarwinism/ModernSynthesis 2. Major transitions in Evolution 3. Geological Timescales 4. Some drivers of evolution
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Mini-summary of week 1
Specific Questions/Comments
Geologists (Hutton, Lyell):Uniformitarianism: Changes in nature are gradual.
In 1800s, fossils showed species that no longer existed:
Some (e.g. Cuvier): !Catastrophism: Fossils show extinct species (due to major, sudden, catastrophic events).
3 Schools of evolutionary thought
• Lamarck: characteristics acquired by an individual are passed on to offspring.
• Linneaus: each species was separately created.
• Darwin & Wallace: evolution as descent with modification.
Evolution by Natural Selection• There is inherited variation within species.!
• There is competition for survival within species.!
• Genetically inherited traits affect reproduction or survival. Thus the frequencies of variants change.
(Not just numbers of offspring!)
Evolutionary fitness:A measure of the ability of genetic material to perpetuate itself in the course of evolution. Depends on the individual’s ability to survive, the rate of reproduction and the viability of offspring.!
1. The Fossil Record2. Comparative Anatomy3. Comparative Embryology4. Vestigial Structures5. Domestication (artificial selection)
Darwin’s evidence for evolution
Paperback 596 pages !(11 Aug 2005)!!Publisher : Oxford University Press!
!
• Also: !• genetic drift!• (sexual selection)!• artificial selection (selective breeding)!• mutation
Natural selection leads to adaptive change
• But environmental conditions change: What was advantageous yesterday may be a disadvantage today.
Evolution=change doesn’t only occur by natural selection!!
“Neo-Darwinism”or
“The Modern Synthesis”The same thing... but with better understanding of
how things work.
• Darwin’s Theory of Evolution by Natural Selection (1859)!• Mendel’s Laws of Heredity (1866, 1900; see SBS 008)!• Cytogenetics (1902, 1904 - )!• Population Genetics (1908; see Lectures 7-12) !• Molecular genetics (1970s- ; see SBS 633/210 and Lecture 6)
•More stuff since then (cultural evolution, epigenetics, etc...)
Gregor Mendel (1822-1884)
Worked out the basic laws of inheritance:!1. Segregation !2. independent
assortment
Austrian Monk,!"father of genetics"
Published “Experiments on Plant Hybridization” in 1865/1866
J.B.S. Haldane (1892-1964)
With Fisher and Wright, one of the founders of population genetics.
first major contribution explaining natural selection in terms of mathematical consequences of mendelian genetics.
“The Causes of Evolution” (1932)
modern evolutionary synthesis
Great science populariserHybridization & speciation
J.B.S. Haldane (1892-1964)
•“The Creator, if He exists, has a special preference for beetles.” (observing that 25% of known species are beetles)!
•coined the word “clone” (from the Greek word for twig) in his speech “Biological Possibilities for the Human Species of the Next Ten Thousand Years” (1963),!
• “Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we CAN suppose”
R.A. Fisher (1890-1962) Major contributions:!• Statisticts (lots) - e.g.
Analysis of Variance!• Experimental Design!• Theory of population
genetics!• 1930 book: ” The Genetical
Theory of Natural Selection.”
Theodosius Dobzhansky (1900-1975)
“Nothing in Biology makes sense except in the light of evolution”. !
!
Genetics and the Origin of Species, published in 1937.
Combined:!• lab work with study of variation in the wild!• European & US research cultures
Ernst Mayr (1904-2005) • Definition of species!• How species evolve
William D. Hamilton (1936 - 2000)
Explained how natural selection acts on social behaviour (“kin selection”)
relatedness * benefit > cost
Explained weird (i.e. unequal) sex ratios
John Maynard-Smith (1920-2004) Most widely known for
•two-fold cost of sex:
•applying game theory to evolutionary biology
1. finding a mate!2. only � have babies
• Dawkins summarized & popularized the kin selection arguments of W. D. Hamilton, George R. Price and John Maynard Smith
1976
Summary/overview
EVOLUTION!“descent with modification”
Patterns and processes in evolutionary thought
New hypotheses
New understanding of evolutionary!
processes
New research
New findings/
observations
• Fossil record!• Dating methods!• Molecular evolution!• Molecular clocks!• Population genetics
• Mechanisms!• Environmental drivers!
•climate!•continental drift!•extinctions...
The Modern Synthesis
EVOLUTION!“descent with modification”
New hypotheses
New understanding of evolutionary!
processes
New research
New findings/
observations
What next?• Epigenetics!
• Cultural transmission!
• Niche construction
“Extended Evolutionary Synthesis” ?
• Evodevo!
• Comparative genomics!
• Systems Biology
“Postmodern Synthesis” ?
Schedule
1. Major transitions in evolution
2. Geological timescales!
3. Major geological drivers of evolution !
4. Recent major extinction events
Major transitions?1. Smaller entities coming together to form larger entities. (e.g.
eukaryotes, multicellularity, colonies...)!
2. Smaller entities become differentiated as part of larger entity. (e.g. organelles, anisogamy, tissues, castes...)!
3. Smaller entities are often unable to replicate without the larger entity. (e.g. organelles, tissues, castes...).!
4. The smaller entities can disrupt the development of the larger entity, (e.g. Meiotic drive, parthenogenesis, cancer...)!
5. New ways of transmitting information arise (e.g. DNA-protein, indirect fitness...)
Maynard Smith and Szathmary 1995
Major transitions: early life
1953 Miller-Urey “primitive soup” experiment
350° vs 0°
➔ organic molecules
Major transitions: early life
•Organic molecules ≠ Life!•Early life:!
•Hereditary replication!•Compartmentalization!!
•First hereditary information?
Phylogenetic Tree of Life
BacteriaGreen
FilamentousbacteriaSpirochetes
Grampositives
ProteobacteriaCyanobacteria
Planctomyces
BacteroidesCytophaga
Thermotoga
Aquifex
HalophilesMethanosarcina
MethanobacteriumMethanococcus
T. celerThermoproteus
Pyrodicticum
Entamoebae Slimemolds Animals
Fungi
PlantsCiliates
Flagellates
Trichomonads
Microsporidia
Diplomonads
Archaea Eukaryota
last universal common ancestor (LUCA)
Woese 1990 tree based on ribosomalRNA sequences
Major transitions: early life
•Organic molecules ≠ Life!•Early life of simple replicators:!
•Hereditary replication!•Compartmentalization!!
•First hereditary information?!•Probably RNA: Genetic information (that can be copied)
+ Enzymatic activity.
•Amino-acids (initially as co-factors)!•DNA (much more stable than RNA)!•Linkage of replicators (chromosomes)
Major transitions: Prokaryote to Eukaryote
Prokaryotic cell
Cell membrane infoldings
Cell membrane
Cytoplasm
Nucleoid(containing DNA)
Endomembrane system
Endoplasmic reticulumNuclear membrane
Nucleus
Proteobacterium
Mitochondria
Cyanobacterium
Chloroplasts
Mitochondrion
†
†
†
1 A prokaryote grows in size and develops infoldings in its cell membrane to increase itssurface area to volume ratio.
2 The infoldings eventually pinch off from the cell membrane, forming an early endomembrane system. It encloses the nucleoid, making a membrane-bound nucleus.This is the first eukaryote.
3
5 Some eukaryotes go on to acquire additional endosymbionts—the cyanobacteria, a group of bacteria capable of photosynthesis. They become chloroplasts.
Ancestor of plants and algæ
Ancestor of animals, fungi, and other heterotrophs
First eukaryote
The aerobe's ability to use oxygen to make energy be-comes an asset for the host, allowing it to thrive in an in-creasingly oxygen-rich environ-ment as the other eukaryotes go extinct. The proteobacterium is eventually assimilated and becomes a mitochondrion.
Some eukaryotes go on to ac-quire additional endosymbionts — the cyanobacteria, a group of bacteria capable of photosynthe-sis. They become chloroplasts.Anaerobic (oxygen using) proteo-
bacterium enters the eukaryote, either as prey or a parasite, and manages to avoid digestion. It becomes an endosymbiont, or a cell living inside another cell.
Major transitions: sex
•See later lectures Week .
Major transitions: multicellularity
Major transitions: multicellularityGreen algae: Inspiration for what may have occurred: Volvocales
Major transitions: multicellularityGreen algae: Inspiration for what may have occurred: Volvocales
e.g.: artificial selection for multicellularity in S. cerevisiae yeast
Ratcliff et al 2012
Major transitions: multicellularityGreen algae: Inspiration for what may have occurred: Volvocales
VolvoxSomatic cells
Gonidia
Major transitions: eusociality
•Solitary lifestyle --> Eusociality!1. Reproductive division of labor !2. Overlapping generations (older
offspring help younger offspring)!3. Cooperative care of young!
Eg: ants, bees, wasps, termites. But also: naked mole rats, a beetle, a shrimp...
Hamilton, 1964
Major transitions: eusociality!
• Hamilton’s rule: genes for altruism increase in frequency when:
indirect fitness benefits to the receiver (B) ,
B
exceeds costs to the altruist (C).
> Cr ₒ
reduced by the coefficient of relatedness (r) !between altruist & receiver,
•General framework: Kin selection: can favor the reproductive success of an organism's relatives (ie. indirect fitness), even at a cost to the organism's own survival and reproduction.
© Alex Wild & others
Similar diversity of lifestyles!
© National Geographic
Atta leaf-cutter ants
© National Geographic
Atta leaf-cutter ants
© National Geographic
Atta leaf-cutter ants
Oecophylla Weaver ants
© ameisenforum.de
© ameisenforum.de
Fourmis tisserandes
© ameisenforum.de
Oecophylla Weaver ants
© forestryimages.org© wynnie@flickr
Tofilski et al 2008
Forelius pusillus
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night
Avant
Workers staying outside die« preventive self-sacrifice »
Tofilski et al 2008
Forelius pusillus hides the nest entrance at night
Dorylus driver ants: ants with no home
© BBC
Animal biomass (Brazilian rainforest)
from Fittkau & Klinge 1973
Other insects AmphibiansReptiles
Birds
Mammals
!Earthworms
!!
Spiders
Soil fauna excluding earthworms,
ants & termites
Ants & termites
Schedule
1. Major transitions in evolution!
2. Geological timescales
3. Major geological drivers of evolution !
4. Recent major extinction events
“Complexity of life” didn’t increase linearly.
2. Geological time scalesDefined by changes in flora and fauna (seen in fossil record).
Eon > Era > Period > Epoch!
4550 Ma:
HominidsMammalsLand plantsAnimalsMulticellular lifeEukaryotesProkaryotes
Hadean
Arch
eanProterozoic
Paleozoic
Mesozoic
Cenozoic
4527 Ma:Formation of the Moon
4.6 Ga
4 Ga
3.8 Ga
3 Ga
2.5 Ga
2 Ga
1 Ga
542 M
a
251 Ma65 Ma ca. 4000 Ma: End of the
Late Heavy Bombardment;first life
ca. 3500 Ma:Photosynthesis starts
ca. 2300 Ma:Atmosphere becomes oxygen-rich;
750-635 Ma:Two Snowball Earths
ca. 530 Ma:Cambrian explosion
ca. 380 Ma:First vertebrate land animals
230-65 Ma:Dinosaurs
2 Ma:First Hominids
Ga = Billion years agoMa = Million years ago
Eon
Eon
Eon
EraEra
Era
Phaneroz
oic!
Eon
Geological timescales: Eon > Era > Period > Epoch
End of Proterozoic biota
Dickinsonia
4550 Ma:
HominidsMammalsLand plantsAnimalsMulticellular lifeEukaryotesProkaryotes
Hadean
Arch
eanProterozoic
Paleozoic
Mesozoic
Cenozoic
4527 Ma:Formation of the Moon
4.6 Ga
4 Ga
3.8 Ga
3 Ga
2.5 Ga
2 Ga
1 Ga
542 M
a
251 Ma65 Ma ca. 4000 Ma: End of the
Late Heavy Bombardment;first life
ca. 3500 Ma:Photosynthesis starts
ca. 2300 Ma:Atmosphere becomes oxygen-rich;
750-635 Ma:Two Snowball Earths
ca. 530 Ma:Cambrian explosion
ca. 380 Ma:First vertebrate land animals
230-65 Ma:Dinosaurs
2 Ma:First Hominids
Ga = Billion years agoMa = Million years ago
Eon
Eon
Eon
EraEra
Era
Phaneroz
oic!
Eon
Geological timescales: Eon > Era > Period > Epoch
50100150200250300350400450500 0542
0
1
2
3
4
5
Millions of Years Ago
Thou
sand
s of
Gen
era
Cm O S D C P T J K Pg N
Biodiversity during the PhanerozoicAll Genera
Well-Resolved GeneraLong-Term Trend
The “Big 5” Mass Extinctions
Other Extinction Events
Cambrian
Trilobites
Cambrian to late permian17,000 known species!
50100150200250300350400450500 0542
0
1
2
3
4
5
Millions of Years Ago
Thou
sand
s of
Gen
era
Cm O S D C P T J K Pg N
Biodiversity during the PhanerozoicAll Genera
Well-Resolved GeneraLong-Term Trend
The “Big 5” Mass Extinctions
Other Extinction Events
Cambrian
Permian Triassic Jurassic
4550 Ma:
HominidsMammalsLand plantsAnimalsMulticellular lifeEukaryotesProkaryotes
Hadean
Arch
eanProterozoic
Paleozoic
Mesozoic
Cenozoic
4527 Ma:Formation of the Moon
4.6 Ga
4 Ga
3.8 Ga
3 Ga
2.5 Ga
2 Ga
1 Ga
542 M
a
251 Ma65 Ma ca. 4000 Ma: End of the
Late Heavy Bombardment;first life
ca. 3500 Ma:Photosynthesis starts
ca. 2300 Ma:Atmosphere becomes oxygen-rich;
750-635 Ma:Two Snowball Earths
ca. 530 Ma:Cambrian explosion
ca. 380 Ma:First vertebrate land animals
230-65 Ma:Dinosaurs
2 Ma:First Hominids
Ga = Billion years agoMa = Million years ago
Eon
Eon
Eon
EraEra
Era
Phaneroz
oic!
Eon
Geological timescales: Eon > Era > Period > Epoch
Dimetrodon!(sub-class Synapsida = “mammal-like reptiles”)
Early Permian mammal-like reptiles
4550 Ma:
HominidsMammalsLand plantsAnimalsMulticellular lifeEukaryotesProkaryotes
Hadean
Arch
eanProterozoic
Paleozoic
Mesozoic
Cenozoic
4527 Ma:Formation of the Moon
4.6 Ga
4 Ga
3.8 Ga
3 Ga
2.5 Ga
2 Ga
1 Ga
542 M
a
251 Ma65 Ma ca. 4000 Ma: End of the
Late Heavy Bombardment;first life
ca. 3500 Ma:Photosynthesis starts
ca. 2300 Ma:Atmosphere becomes oxygen-rich;
750-635 Ma:Two Snowball Earths
ca. 530 Ma:Cambrian explosion
ca. 380 Ma:First vertebrate land animals
230-65 Ma:Dinosaurs
2 Ma:First Hominids
Ga = Billion years agoMa = Million years ago
Eon
Eon
Eon
EraEra
Era
Phaneroz
oic!
Eon
Geological timescales: Eon > Era > Period > Epoch
Earth
Life
Eukaryotes
Homo sapiens: 5 meters
Whitechapel: Dinosaurs extinct
NHM
: first tetrapod
Ham
mersm
ith: Cam
brian explosion
Schedule
1. Major transitions in evolution!
2. Geological timescales!
3. Major geological drivers of evolution
4. Recent major extinction events
3. Major geological drivers of evolution
•Tectonic movement (of continental plates)!
•Vulcanism!
•Climate change!
•Meteorites
Conditions on earth change.
Plate tectonics
12
354
Crustal plates and continental drift
Recent continental movements...
TETHYS SEA
LAURASIA
GONDWANA
EquatorTriassic 200 Mya
Pangaea - single supercontinent
Fossil distribution
Gondwana
Earthquakes
•Some tectonic movement is violent.!
•E.g. 2004 Sumatra earthquake & tsunami...
Vulcanism•Local climate change (e.g. thermal vents, hot springs...)!
•Global climate change: Emission of gasses & particles.!
•New geological barriers (migration...)!
•New islands (“Malay archipelago”, Galapagos... Hawaii... )
Deccan traps
Eyjafjallajokull
Climate change(since Cambrian)
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