Introduction to Health and Disease

• Evolution


  The process of change in heritable characteristics (allele frequency) affecting the genotype and phenotype
• Natural selection


  1. Variation in survival and reproductive success

  2. Variation in traits

  3. Correlation between traits and survival/reproductive success

  4. Heritability of traits
• Evolution is not random
• Evidence for evolution


  • Direct observation
  • Fossils
  • Comparative anatomy and embryology
  • Biogeography
  • Molecular biology
• Evolutionary fitness


  The ability to survive to reproductive age, attract a mate, produce live offspring, and ensure the survival of subsequent generations
• Adaptive physiological trait


  A trait that is advantageous in the current environment
• Not all existing physiological traits are adaptive
• Evolutionary mismatch


  Traits that were advantageous in past evolutionary environments become less beneficial or even harmful in the current environment
• Types of evolutionary mismatch

  • Mismatch in time
  • Mismatch in space
• Evolutionary mismatch in time

  • Traits adaptive for hunting (efficient metabolism of a varied diet and high physical activity levels) becoming less beneficial in the agricultural era
• Evolutionary mismatch in space


  • Organisms moving from environments where they are well adapted to environments where they are not (e.g. migration leading to issues with thermoregulation, vitamin D deficiency, unfamiliar pathogens, allergens and dietary components)
• Spandrel


  A phenotypic characteristic that arises as a byproduct of the evolution of other traits, rather than being directly selected for through adaptive processes
• Spandrel


  • Appendix - may serve as a reservoir for beneficial gut bacteria (accidentally helpful)
• Perspectives on health


  • Absence of disease/disability
  • Relative to experience and expectation and/or absence of disability from some cultural average
  • Changing with age or as new normals are reached if a condition is persistent
• Classifications of disease


  • Diseases with genetic causes
  • Diseases with environmental causes
  • Diseases that are by-products/cost of defence systems
  • Diseases of homeostasis
  • Diseases of lack of maintenance
  • Diseases caused by random developmental problems
  • Diseases of pregnancy and/or early development