Lecture #11 Date ________ Chapter 24 ~ The Origin of Species

Patterns In Time Formation of the Earth = 4.6 billion years agoFormation of the Earth = 4.6 billion years ago Age of the Dinosaurs = 65 – 225 million years agoAge of the Dinosaurs = 65 – 225 million years ago Were you there? How do we know this?

Relative Dating Methods Stratigraphy – studying the layers of sedimentary rockStratigraphy – studying the layers of sedimentary rock Oldest layers on the bottom, youngest layers on the topOldest layers on the bottom, youngest layers on the top Two objects in the same layer are approximately the same ageTwo objects in the same layer are approximately the same age

Direct Dating Methods Accurately determines the age of a rock or fossilAccurately determines the age of a rock or fossil Uses the regular breakdown rate of certain chemicals (Potassium, Uranium, Carbon 14)Uses the regular breakdown rate of certain chemicals (Potassium, Uranium, Carbon 14) Half-life – the amount of time it takes for half of a specific chemical to breakdown.Half-life – the amount of time it takes for half of a specific chemical to breakdown.

Radioactive isotopes Potassium – Argon dating K40  Ar40 (half-life = 1.3 billion years)Potassium – Argon dating K40  Ar40 (half-life = 1.3 billion years) Uranium – Lead dating U238  Pb206 (half-life = 4.5 million years)Uranium – Lead dating U238  Pb206 (half-life = 4.5 million years) Carbon 14 dating C14  N14 (half-life = 5730 years)Carbon 14 dating C14  N14 (half-life = 5730 years)

Macroevolution: the origin of new taxonomic groups Speciation: the origin of new speciesSpeciation: the origin of new species 1- Anagenesis (phyletic evolution): accumulation of heritable changes1- Anagenesis (phyletic evolution): accumulation of heritable changes 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

What is a species? Biological species concept (Mayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)Biological species concept (Mayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

Reproductive Isolation (isolation of gene pools), I Prezygotic barriers: impede mating between species or hinder the fertilization of the ovaPrezygotic barriers: impede mating between species or hinder the fertilization of the ova Habitat (snakes; water/terrestrial)Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling)Behavioral (fireflies; mate signaling) Temporal (salmon; seasonal mating)Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy)Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors)Gametic (frogs; egg coat receptors)

Reproductive Isolation, II Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adultPostzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity) Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)Reduced hybrid fertility (mule; horse x donkey; cannot backbreed) Hybrid breakdown (cotton; 2nd generation hybrids are sterile)Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

Modes of speciation (based on how gene flow is interrupted) Allopatric: populations segregated by a geographical barrier; can result in adaptive radiation (island species)Allopatric: populations segregated by a geographical barrier; can result in adaptive radiation (island species) Sympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishesSympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

Punctuated equilibria Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil recordTempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record