Ch. 23- Broad Patterns of Evolution

Ch. 23- Broad Patterns of Evolution

1. Fossil Record

   • Fossils are found in Sedimentary rocks
   • Fossil record has not preserved organisms that survived for a shorter time and who did not have shells/skeletons that facilitated fossililization
   • Dating
     • 0-75,000 YA
       • Radiometric Dating
         • All organisms contain carbon-14 and Carbon-12. Carbon-14 decays, but carbon-12 does not. Scientists compare amoutns of carbon-12 and carbon-14, using the half-life of carbon-14 to assay how hold the fossil is
     • 75,000 + YA
       • Strata Analysis
         • A fossil is stuck between two strata of rock. the strata around the fossil have trapped radioisotopes in them that have very long half lives. Scientists can determine the age of the surrounding strata, and then take an average to discover how old the sandwiched fossil is.
   • Origins of New Groups of Organisms
     • Tetrapods= mammals, amphibians, and reptiles
       • Mammals can be distinguesed from other tetrapods: the jaw is only one bone. the jaws hinge in different ways. they have 3 miniature bones in the middle ear. Mammal teeth are differentiated into the incissors, canines, and molars.

2. Biogeography

   • Continental Drift- movements in the mantle cause plate tectonics in the crust to move over time
     • Continental drift can cause changes in environment and climate, upon which natural selection acts
     • Hugely promotes ALLOPATRIC SPECIATION
   • Mass Extinctions
     • 99% of species that ever lived are now extinct
     • Permian Mass extinction
       • 1.6 million square km was covered in a 100-1000 m thick layer of lava. The eruptions produced CO2 that warmed clobal climate by 6 decrees C. Temperature differences slowed the mixing of water, creating a ocean anoxia. This suffocated oxygen breathers and selected for anaerobic bateria that produced the poisonous side product H2S which directly killed organisms and destroyed chunks of the ozone layer.
   • Adaptive Radiations
     • periods of evolutionary change (ex. after a mass extinction) in which groups of organisms form many new species whose adaptations allow them to fill different ecological niches in their communities
     • each mass extinction lead to a large-scale adaptive radiation because they left many vacant ecological niches

3. Evo-Devo

   • slight genetic differences produce major morphological differences b/w species
   • heterochrony is an evolutionary change in the rate or timing of developmental events
     • difference in timing/rate of bone growth in skulls of chimps vs humans
   • Homeotic and hox genes

4. Evolution is not goal oriented

   • evolution of the eye= independently evolved from basic structure/ incremental increases in modifications tat benefited the owner at each stage
   • Exaptations- structure has evolved in one context but becomes co-opted for another purpose
     • Natural selection does not predict the future, it only improves a structure in the context of its current utility