Chapter 3 - Natural Selection and Adaptation

• Natural selection


  Any consistent difference in fitness among different classes of biological entities
• Fitness


  Sometimes called reproductive success, which includes survival because organisms do not reproduce when they are dead. A simple way to think of fitness is as the number of offspring an individual leaves in the next generation. The components of fitness are SURVIVAL AND REPRODUCTION.
• Evolution by natural selection occurs if

  1. There is a correlation between an individual's phenotype and its fitness

  2. Variation in the phenotype is correlated between parents and their offspring
• Culture


  Information capable of affecting individuals' behavior that they acquire from other members of their species through teaching, imitation, and other forms of social transmission
• Natural selection is not synonymous with evolution. Natural selection can occur without any evolutionary change, as when natural selection maintains the status quo by eliminating deviants from the optimal phenotype. And processes other than natural selection can cause evolution.
• Neutral alleles


  Those that do not alter fitness: the average reproductive success does not differ between individuals that carry one neutral allele or the other
• Levels of selection


  • Genes
  • Individual organisms
  • Groups
  • Species
• Selfish genes


  Genes that prioritize their own survival over the survival of the organism
• Unselfish behaviors


  Actions that prioritize the needs of others over one's own
• Adaptation


  The evolutionary process by which, over the course of generations, organisms are altered to become improved with respect to features that affect survival or reproduction
• Adaptation


  A characteristic of an organism that evolved by natural selection
• Preadaptation


  A feature that fortuitously serves a new function
• Exaptation


  Adaptation of a trait for a purpose other than the trait was evolved for
• Evidence for selection from DNA sequences

  • Complexity - Even if we cannot immediately guess the function of a feature, we often suspect it has an adaptive function if it is complex, for complexity cannot evolve except by natural selection
  • Design - The function of a character is often inferred from its correspondence with the design an engineer might use to accomplish some task, or with the predictions of a model about its function
  • Experiments - Experiments may show that a feature enhances survival or reproduction, or enhances performance (locomotion or defense) in a way that is likely to increase fitness, relative to individuals with other features
• Darwin noted that "natural selection will not produce absolute perfection, nor do we always meet, as far as we can judge, with this high standard in nature". Selection can fix only those genetic variants with a higher fitness than other genetic variants in a particular population at a particular time. It cannot fix the best of all conceivable variants if they do not arise, or have not yet arisen, and the best possible variants often fall short of perfection because of various constraints.
• Character displacement


  Divergence of species as a consequence of their interaction
• The optimal feature, the character that maximizes fitness, depends on the context in which it functions