Evolution and speciation

• Evolution


  Change in heritable characteristics of a population
• Lamarck's theory of giraffe evolution

  • Evolution is acquired, ancestors stretched their neck to eat leaves
  • The stretching was passed onto the offspring
• Darwin's theory of giraffe evolution

  • Some giraffes are long necked, they survive and pass it onto offspring
  • Occurs due to selective pressures, better organism survives better
• Evidence for evolution


  • RNA/amino acid/DNA
  • Homologous structures
  • Selective breeding
• Selective breeding


  • Selection where humans choose which traits should be passed on
  • Natural variation occurs, seeds with desirable traits chosen, over time quality increases
  • Provides evidence that selection can cause evolution on a short geologic time scale
  • Does not prove that evolution occurs naturally
• Homologous structures


  • Common structures different species have
  • Limbs of vertebrates are very similar, used in different ways
  • Evidence of divergent evolution, common ancestor
  • Pentadactyl limbs
• Analogous structures


  • Different structures, different function, not from a common ancestor
  • Bird and insect wings, squid and human eyes
• Processes required for speciation

  1. Reproductive isolation -> separation of genes and divergence

  2. Differential selection -> significant difference in natural selection, traits become very different
• Sympatric and allopatric isolation

  • Allopatric - geographic isolation, physical separation
  • Sympatric - divides into two species while in the same habitat
  • Behavioral - courtship behavior, different songs
  • Temporal - different mating times, cicadas
• Adaptive radiation


  • Allows closely related species to coexist without competing
  • Evolution of 1 ancestral species into several species, spreads and adapts to environmental niches
  • Ecological niche - the role of an organism in an ecosystem
• Barriers to hybridization


  • Sterile hybrid (mule)
  • Courtship behaviors
  • Hybrids are generally sterile and not considered a species
  • Pre-zygotic barriers - behavioral, temporal, ecological, mechanical
  • Post-zygotic barriers - hybrid unviability, hybrid infertility, hybrid breakdown
• Abrupt speciation in plants by hybridization and polyploidy

  • Polyploidy - more than two sets of chromosomes
  • Autopolyploid - polyploidy arising in a species
  • Allopolyploid - polyploidy due to hybridization of 2 distinct species
• Gradualism


  Slow change through a series of intermediate forms
• Abrupt speciation/punctuated speciation


  • Long periods of stability punctuates by periods of rapid evolution
  • No long sequence of intermediates
• Polyploidy is common in knotweeds
• Polyploid plants


  • Usually produce bigger fruits
  • Plants with even sets of chromosomes can reproduce sexually