Variation and Selection

• Variation - Usually caused by differences in the genotype or by environmental factors.
• Continuous Variation - Gradual change in a characteristic across a population e.g., height.
• Discontinuous Variation - Population can be clearly divided into discrete groups / categories.
• Natural Selection

  1. All organisms produce more young than can survive.
  2. Variation in a population.
  3. Competition causes struggle for existence.
  4. Better adapted individuals survive - survival of the fittest.
  5. Better adapted are more likely to survive to breed.
• Extinction - Process that results in no living individuals of a certain species surviving.
• Endangered - Species is at risk of becoming extinct.
• Selective Breeding - deliberately selecting particular characteristics of use to us e.g., increased crop quality, longer shelf life, appearance.