AS

Chapter 1: Adaptation by Natural Selection

  • Adaptation: A feature of an organism created by the process of natural selection
  • Natural Selection: The process that produces adaptation
  • Before Darwin there was no scientific explanation for the fact that organisms are well adapted to their circumstances
  • Darwin’s three postulates of natural selection:
    • Availability of resources is limited; while the ability of a population to expand is infinite, the ability of any environment to support the population is always finite.
    • There is variation among a population, and the variation affects each individual’s ability to survive and reproduce.
    • This variation is heritable and will be transmitted from parent to offspring.
  • Blending inheritance: A model of inheritance, widely accepted during the nineteenth century, in which the hereditary material of the mother and father was thought to combine irreversibly in the offspring.
  • Morphology: The form and structure of an organism; also a field of study that focuses on the form and structure of organisms.
  • Equilibrium: A steady state in which the composition of the population does not change.
  • Stabilizing selection: Selection pressures that favor average phenotypes. Stabilizing selection reduces the amount of variation in the population but does not alter the mean value of the trait.
  • Traits: A characteristic of an organism
  • Characters: A trait or attribute of the phenotype of an organism.
  • Species: A group of organisms classified together at the lowest level of the taxonomic hierarchy. Biologists have different opinions on how to define a species.
  • Fecundity: The biological capacity to reproduce. In humans, fecundity may be greater than fertility (the actual number of children produced) when people limit family size.
  • Continuous variation: Phenotypic variation in which there is a continuum of types.
    • Ex: Height in humans is an example of continuous variation.
  • Discontinuous variation: Phenotypic variation in which there is a discrete number of phenotypes with no intermediate types.
    • Ex: Pea color in Mendel's experiments is an example of discontinuous variation.
  • Convergence: The evolution of similar adaptations in unrelated species. The evolution of camera-type eyes in both vertebrates and mollusks is an example of convergence.
    • Sometimes unrelated species have independently evolved the same complex adaptation, suggesting that the evolution of complex adaptations by natural selection is not a matter of mere chance.
    • Complex adaptations can arise through the accumulation of small random variations by natural selection.
  • Placental mammals: A mammal that gives birth to live young that developed for a period of time in the uterus and were nourished by blood delivered to a placenta.
  • Marsupials: A mammal that gives birth to live young that continue their development in a pouch equipped with mammary glands. Marsupials include kangaroos and opossums