Lecture 2 Evidence For Evolution Flashcards
Before Darwin
Species considered to be ‘immutable units of God’s creation’ Genesis
Perfect adaptation accredited to God’s power
17th century Bishop James Ussher calculated that the Earth was created 6pm Saturday 22/10/4004 BC
By 19th century geologists show that landscapes were formed by wind and water not created in present form
Jean Baptiste Lamarck (1744-1820)
1) All animals have innate power to progress or adapt within their lifetime
2) environment causes need to change
3) characteristics acquired during life transmissible from one generation to another e.g. giraffes neck extending or blacksmiths atm building muscle X giraffes cannot extend neck further than genetically inherited in lifetime predisposition to gain mus le may be inheritable though
Charles Darwin
1) random heritable variations exist within species - diff individuals have diff adaptations pos and neg
2) large abrupt changes are rare, most are gradual e.g. selective breeding of dogs or pigeons
3) small variations improve suitability to local environment maintained/increased by natural selection
4) limited resources -> struggle for existence -> survival of the fittest
Darwin’s influences
Charles Lyle: geologist, taught Darwin rock layers define age of fossils
Alfred Russell Wallace (1823-1913) - encouraged Darwin to write origin of species. He’d reached similar conclusions and they published a paper together
Herbert Spencer coined term survival of the fittest
Thomas Huxley also influential
Gradualism Vs punctualism
Grad- evol via change in gene freq over time
Punct- evol in leaps after long periods of stasis - would explain fossil record gaps
Rate of evolution is still debated
Blending inheritance
Darwin had no idea about heredity postulated ‘blending inheritance’ Mendel had published his inheritance research in 1862 unbeknown to Darwin
Domestication
Artificial selection for certain traits
Reveals vast reservoirs of genetic info e.g. breeding dogs
Can lead to neg effects e.g. resistance in insect pests and antibiotic resistance
Peppered moth (Boston Betularia)
Example of artificial selection
White form camouflaged on lichen covered trees became visible on soot covered trees during industrial revolution making them vulnerable to predators. Melanic (dark) variety selected for.
biogeographic evidence of evolution
Latitude & altitude determine genetic variation as do plate tectonics by isolation/combination
Phylogenesis
Radioisotopic dating of rocks to interpret fossils of known ages
Fossils
From ‘fossilis’ meaning obtained by digging in Greek
Late 18th century: associating fossils w/specific rock strata gave rise to idea of geological time scale (stratigraphy)
Fossil record: combination of fossils over multiple strata of known age infers change over time as recognised by Darwin
Fossils: radiometric dating of rocks
Became possible early 1900’s
Rate of radioactive decay (half life) used to match to timescale
C14 good to date recent historic items but half life too short for fossils
Rb87 robidium w/ half life 48.8 BY to convert to Sr87. A stable isotope Sr86 is also present providing ratio to estimate a rocks age
Fossilised melanosomes
Pigment cells
Found in feathers of fossilized birds and in integumentary filaments of their dinosaur ancestors providing evidence of barring and pigmentation on early feathers
Models and mechanics from anatomical information
As body vol. Increases legs become proportionally broader to support it so a body weight of 140 tonnes would need legs so wide that they touch so no animal can exceed this size
Problems w/fossil evidence 1-5
1) most organisms don’t fossilize - get eaten/decompose. Conditions for fossilization v. Specific require settlement of fine sediment over hard structures and infiltration into pores
2) soft tissues e.g. muscles rarely mineralise - fossilisation of soft tissue requires anoxic mud aka Lagerstatten sites which are v. Rare
3) most rock inaccessible to palaeontologists so most digging only in ‘hot spots’
4) gaps in fossil records give discontinuous info on evolutionary patterns
5) interpretation contentious (disputable) difficult to gather evidence - compare w/extant groups, estimate divergence of taxa and ‘molecular clocks’ ( rate of base pair substitution)
Problems w/fossil evidence 6-10
6) dating can be tricky - rocks/sediments churned by geological activity
7) diff rock types and geo. periods vary in suitability to enable fossilization affecting fossil availability
8) availability of rock outcrops of diff. geological ages cause bias requiring correction
9) difficult to distinguish species from limited anatomical details biological species concept cannot be invoked
10) Dangerous to infer behaviours from anatomy
Mass extinctions: Ordivician event
Ending 443MYA
Within 3.3-1.9 MY 57% of genera (Est. 86% spp) lost due to raising/lowering of sea levels from glacial cycles and changes in sea chemistry
Mass extinctions: Devonian Event
Ended 359MYA
Within 29-2 MY 35% genera (est. 75% spp) lost due to global cooling/warming, marine anoxia, meteorites (?)
Mass extinctions: Permian event
Ended 359 MYA
Within 2.8 MY - 160 KY 56% genera ( est. 96% spp) lost due to volcanism, warming, marine anoxia, high CO2 and low O2.
Mass extinction: Triassic event
Ended 200 MYA
Within 8.3MY to 6000KY 47% genera (est. 80% spp) lost due to marine volcanic activity, elevated CO2 warming and calcification crisis in oceans
Mass extinction: Cretaceous event
Ended 65 MYA
Within 2.5 MYA - <1 year ( potentially very rapid) 40% genera (est. 76% spp) lost due to meteorite impact on Yucatan peninsula Mexico - thought to have caused global cataclysm and rapid cooling. Preceding impact biota already declining due to volcanism, CO2 increase, global warming and ocean anoxia episodes
Mass extinctions: the sixth?
Current extinction rates are approaching equivalent magnitude and speed to past events due to anthropogenic cause ( based on Baronsky et al. 2011)
