bio1b evolution 12 - integrative biologyib.berkeley.edu/.../evolutionspring11/pdfs/moritz12.pdf ·...
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Bio1B Evolution 12Last lecture: Fossil recordFossil record - significance & interpretationExtinction -Background extinction rates and the “big 5” mass extinctionThe “K/T” boundary - asteroid hypothesis; dinosaur extinctions, radiation
of mammalsAre humans causing the 6th mass extinction?
TodayMacro-evolution (cont.)Species selectionTransitional forms - tetrapods, birds: “exaptation”Evolution of developmental programs - eg. vertebrate limbs
Human evolutionEvolutionary origins of Homo sapiens: fossils & molecular evidence
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Are we the cause of the 6th massextinction? (Barnosky et al. Nature 2011)
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Macro-evolution: Species selection
Evolution of particular trait (red)consistently associated withincreased rate of diversification (fromRabosky & McCune 2010 TREE)
BUT -diversificationrate (S-E) -higher in SI(purple) thanSC (blue)
E.g. self incompatibility (SI) in hermaphroditic plants isoften disdadvantageous within species compared toself-compatibility (SC)
E E Goldberg et al.Science 2010;330:493-495
SI
SC
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Understanding the transition of tetrapodvertebrates from water to land
Fig 34.20
Tiktaalik
Acanthostega
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Modification of existing structures for newpurposes: ears and feathers
Fig. 34.31. Bones of inner ear ofmodern mammals are derived fromjaw joint of ancestors (see also Fig.25.6
LateJurassicfeathereddinosaur
Feathers:for displayor warmthbeforeflight?
Recent discovery:dinosaur featherswere colored -display?
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Evolution ofdevelopmental genes=> phenotypic novelty
• Molecular homology: geneswith common ancestrycontrolling development (topright)
• Changes in timing andspatial pattern of expression=> change in phenotype
• E.g Ubx suppresses legdevelopment in flies, but notshrimp
Fig. 25.22
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Origin of novelties:The vertebrate limb
• Are the fish “fin” and vertebrate“limb” homologous?
• Very different anatomy, yet…• Similar patterns of Hox gene
expression• Anatomic differences could be due
to modification of timing/duration ofexpression?
Shubin etal. 2009Nature457:818
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Evolution ofhominins: fossil
evidence I
Fig. 34.40
• Hominins split fromcommon ancestor withchimps about 7Myr;African origins, diversityexpands 4-2Myr
• Key features: bipedalism,smaller canines (largebrain later)
• A. ramidus - neitherchimp nor human - seedisplay in VLSB
• “Australopiths” probablyparaphyletic with Homo
“Lucy”
Robustanthropoids
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Evolution of hominins: fossilevidence II
Fig. 34.40
• Homo - key features:increasing brain size,reduced jaw, lower sexdimorphism, moreterrestrial
• African origins; H. erectus-> europe >1.8Myr ->Indonesia (“Java man”).Extinct 200 Kya?
• H. floriensis - >1M? -12Kya. Related to H.erectus?
• Neanderthals - Europeand near east, 200-24Kya
?
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Evolution ofhominins: fossil
evidence IIIH. floriensis• Possibly persistent
relative of H. erectus [ormalformed H. sapiens?]
• Exemplifies humansevolve as other species:dwarfing of largemammals on islands -eg. Stegodon “pygmyelephants & hugelizards! (Varanus)
• Putative tools >1Myr,fossils to 12Kya -overlapping H. sapiens
H. floriensis MicrocephalicH. sapiens
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Migration of H. sapiens• Out of Africa - about
100Kya• Rapid spread across Sth
Asia to Australia & centralAsia
• One or 2 colonizationsacross Bering bridgeduring last ice age ->rapid spread to SthAmerica
• Polynesian migrationsacross Pacific are recent:1500 BC to 300 AD(Hawaii)
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Modern humans &related species -hybridization orreplacement?
Genetic evidence largelysupports single origin & “out-of- Africa” over independentorigins from differentpopulations of H. erectus(multi-regional).
But did modern humanshybridize with, or simplyreplace neanderthals?
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Paleogenomics: Neanderthal v modern humans• 60-38Kya bones of neanderthal
sequenced - compared to differenthuman populations
• 2-3% neanderthal genes ineurasian-papuan, not africans
• Several genes - eg skin &pigmentation, skeleton, metabolismunder recent selection in humans
• Refs: Green et al. 2010 Science 328:710,Gibbons 2010 Science 328:680
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‘Denisovans’ - anotherrecent Homo
Neanderthals
(bottleneck?)
Modernhumans
440-270 Kya
2.5%
4-5%
Reich et al. 2010 Nature 468:1053
50-30Kyafossil