Lecture 5

• Evidence for Evolution
• Two views of the history of life

  • Special creation
  • Descent with modification

  
• Special creation and descent with modification make different claims, which can be checked against the evidence
• Evidence of microevolution


  • Evidence from selective breeding
  • Evidence from the wild
• Evidence from selective breeding

  • Selectively bred mice who voluntarily ran long distances on exercise wheels
  • Four high-runner and four control lines were established using 10 mated pairs each
  • High-running offspring were selected based on the greatest running distance, avoiding sibling breeding
  • Controls were chosen randomly
  • After 24 generations, high-running females ran 2.78 times farther on average than controls
  • Ran faster, not for longer time
  • High-runners and controls differed genetically, physiologically, and morphologically
• Evidence from the wild

  • Optimal field mustard (Brassica rapa) life history is linked to precipitation
  • During a drought, soil dries out quickly after any rain; they must produce seeds quickly, otherwise they leave few descendants
  • Normal conditions favour later flowering: they can grow more and produce more seeds
  • In 2000–2004, Southern California had an extreme drought
  • Seeds collected in Southern California pre-drought (1997) and post-drought (2004) were grown in controlled greenhouse conditions
  • Plants grown from post-drought seeds flowered ~8.6 days earlier
  • Hybrids of pre- and post-drought plants had intermediate flowering time
• Evidence from the wild

  • Threespine stickleback
  • Small marine fish that invades freshwater
  • Marine forms are heavily armoured; freshwater forms have only light plating
  • Armour is controlled by two genes, each with two alleles
  • Marine sticklebacks invaded Loberg Lake, Alaska between 1982 and 1988
  • By 2001, population had evolved such that >75% of individuals had light plating
• Evidence of speciation


  • Evidence from lab experiments
  • Evidence from the wild
• Evidence from lab experiments

  • φ6 is an RNA virus that infects the bacterium Pseudomonas syringae
  • Different strains can interbreed when they infect the same host cell
  • φ6WT is the wild-type strain, which infects P. syringae; mutant φ6broad has extended host range, including P. pseudocaligenes
  • Experiment involved four φ6broad populations on P. pseudocaligenes; cycling through ~150 generations
  • Mutant φ6E1narrow emerged, specialized for P. pseudocaligenes (i.e., it is unable to infect P. syringae)
  • φ6E1narrow showed competitive advantage in P. pseudocaligenes, rising to high frequency in the population
  • Experiment demonstrates virus host-switching and speciation
  • φ6WT and φ6E1narrow infect different bacterial host species; therefore, they cannot interbreed and are different species
• Evidence from lab experiments

  • Experimenters evolved fruit fly populations on different diets: starch-based and maltose-based
  • Diets were stressful, requiring multiple generations to adapt and thrive
  • Mating trials tested for reproductive isolation between diet-adapted populations
  • Flies significantly preferred mates from the same dietary group, indicating a move towards reproductive isolation
  • Despite partial isolation, the flies are not yet separate species
  • But they were only observed for one year (i.e., ~20 generations)!
  • Demonstrates accumulation of reproductive barriers and challenges of observing speciation in real time

  
• Evidence from the wild

  • Differ in gill-raker size: short à eat copepods, long à eat insect larvae
  • Creek vs. lake fish: creek à big; long gill-rakers, lake à small; short gill-rakers
  • Benthic vs. limnetic fish: benthic à big; long gill-rakers, limnetic à small; short gill-rakers
  • Two species
• Evidence from the wild

  • Ring species – chain of interbreeding populations that loops around, such that terminal populations coexist without interbreeding
  • Range of Siberian greenish warbler forms a ring around the Tibetan Plateau
  • Can interbreed around the entire ring, except in central Siberia
  • Genetic distance (and song dissimilarity) increases with distance around the ring
  • Probably descended from a southern population that expanded northeast and northwest; when both met in Central Siberia they could no longer interbreed
• Evidence of macroevolution


  • First appearances in the fossil record
  • Extinction and succession
  • Convergence

  
• Earth formed ~4.6 billion years ago
• First organisms appear ~3.5 billion years ago
• Groups first appear in the fossil record in an orderly, evolutionary fashion
• Many arrive after known fossil transitions from ancestors
• Law of succession


  Fossil assemblages in geological strata show a consistent and predictable order globally, while also exhibiting a noticeable resemblance to the living organisms in the same geographic region
• Convergent evolution


  Different species independently evolve similar traits because they adapt to similar environments or ecological niches
• Under the hypothesis of special creation, why create different mole-like forms in both Eurasia and Australia?
• And why are the marsupial moles only found in Australia with the other marsupials?
• Evidence of common ancestry

  • Extant gradations of complexity
  • Extant transitional forms
  • Extinct transitional forms
• Extant transitional forms


  • Blenniella is aquatic
  • Praealticus is amphibious
  • Alticus is terrestrial (breathes air through gills and skin; can climb vertical surfaces)
  • Display various land-based behaviors, including coordinated hopping and tail twisting, which aid in terrestrial locomotion
  • Terrestrial locomotion is most rudimentary in Blenniella; most advanced in Alticus
  • Traits observed across these species are consistent with common ancestry, with speciation events leading to distinct adaptations in each lineage
  • The amphibious Praealticus is a living example of a transitional form

  
• Extinct transitional forms


  • Evolutionary transition of bones from skull, shoulder girdle, and forelimb: Eusthenopteron (fully aquatic fish) -> Panderichthys (tetrapod-like fish) -> Acanthostega (fish-like tetrapod) -> Greererpeton (fully terrestrial tetrapod)
  • Tiktaalik goes here
  • Odontochelys (~220 mya) had plastron, but no bony carapace; ribs grew out, but not over shoulder blades
  • Archaeopteryx has many features of both non-avian dinosaurs (e.g., teeth, long bony tail, claws) and modern birds (e.g., feathers, reversible toe)
  • Reptiles have an articular–quadrate jaw joint (and stirrup in ear); mammals have a dentary–squamosal jaw joint (and hammer, anvil, and stirrup in ear); fossil record shows dentary taking over lower jaw of ancestral mammals

  
• Archaeopteryx


  • Has plastron, but no bony carapace
  • Ribs grow out, but not over shoulder blades
• Archaeopteryx was described in 2008
• Archaeopteryx has many features of both non-avian dinosaurs (e.g., teeth, long bony tail, claws) and modern birds (e.g., feathers, reversible toe)

  
• Reptile jaw joint


  • Articular–quadrate jaw joint (and stirrup in ear)
  • Vibrations pass from lower jaw to eardrum
• Mammal jaw joint


  • Dentary–squamosal jaw joint (and hammer, anvil, and stirrup in ear)
  • Fossil record shows dentary taking over lower jaw of ancestral mammals
  • Articular evolves into hammer
  • Quadrate evolves into anvil
• Diarthrognathus


  Has a double jaw joint: Articular–quadrate and dentary–squamosal
• Whales are known to be artiodactyls based genetic data
• Ancestral whales also have a double-pulley astragalus: a unique feature of artiodactyls
• Fossil record contains numerous transitional forms showing modification of skull, reduction of hind limbs, evolution of tail fluke, etc.

  
• Hominin fossil record contains many transitional forms

  
• Show adaptations for bipedalism, many modifications of skull
• Neoteny


  Retention of juvenile traits into adulthood
• Humans may have evolved from apes partially through neoteny
• In the 1950s, biologists hypothesized what ancestral ants might have looked like
• Assumed ants evolved from non-social wasps
• In 1967, Sphecomyrma was discovered in amber (~92 million years old)