Ch. 17

• Microevolution is a change in allele frequencies within a population
• Microevolution does not lead to the formation of new species
• Macroevolution, or the origin of a new species, results from the accumulation of microevolutionary changes over time
• Darwin dedicated his life to understanding how new species originate
• Speciation is a form of macroevolution
• Taxonomists are scientists who classify organisms into groups
• Species can be defined in various ways, including:

  • Morphological Species Concept
  • Evolutionary Species Concept
  • Phylogenetic Species Concept
  • Biological Species Concept
• Morphological Species Concept:

  • Species are distinguished by distinct physical characteristics
  • Helpful for paleontologists
  • Challenging for microorganisms and cryptic species
• Evolutionary Species Concept:

  • Members share a distinct evolution in addition to morphological traits
  • Used to indicate speciation in the fossil record
• Phylogenetic Species Concept:

  • Smallest set of interbreeding organisms that share a common ancestor
  • Monophyletic branch in the phylogenetic tree
  • Considers DNA and other factors
• Biological Species Concept:

  • Relies on reproductive isolation to identify different species
  • Reproductive isolation defined by physiological, behavioral, and genetic processes
• Reproductive Isolating Mechanisms:

  Prezygotic Isolating Mechanisms:

  • Geographic Isolation
  • Habitat/Ecological Isolation
  • Temporal Isolation
  • Behavioral Isolation
  • Mechanical Isolation
  • Gamete Isolation

  Postzygotic Isolating Mechanisms:

  • Hybrid Inviability
  • Hybrid Sterility
• Allopatric Speciation is the most common form of speciation:

  • Species separated by a geographical barrier
  • Undergo different selection pressures
  • Competition leads to resource partitioning
• Sympatric Speciation:

  • Speciation without a geographic barrier
  • Involves divergence in diet or microhabitats
  • Polyploidy is more likely in plants
• Adaptive Radiation:

  • A single ancestral species gives rise to a variety of new species
  • Often involves sympatric species and ecological release
• Convergent Evolution:

  • Occurs when biological traits evolve in two unrelated species due to exposure to similar environments
  • Examples include African lake fish with similar coloring/body
• Principles of Macroevolution:

  • Gradualistic model
  • Punctuated equilibrium model
  • Developmental Genes and Macroevolution
• Developmental Genes and Macroevolution:

  • Control switches for development are shared among all organisms
  • Examples include the Pax6 gene for the eye and Tbx5 gene for limbs
• Human Evolution:

  • Humans have approximately 23,000 genes
  • Natural selection acts on variations that are already present
• Macroevolution is not goal-oriented but opportunistic