Natural Selection


Natural Selection in Penguins - a tutorial illustrating how natural selection occurs



  1. All natural populations have the reproductive capacity to exceed the resources that sustain them, however they cannot increase in size indefinitely without running out of food, living space and other resources

    In other words: more young are born than can survive - remember the Grants found this to be true in the finch populations.

  2. Because more young are born than can survive to reproductive age - you can infer that members of a population must compete for the available resources

  3. Individuals of a population differ in the details of their form, function and behavior (remember the slight variations in beak depth and width among the finches). Most of this variation is heritable - passed from parents to offspring - the Grant's found a strong genetic component in beak width and depth.

  4. Some forms of heritable traits are more adaptive (suited to the environment) than others in the competition for resources.

    For example: some finch beaks are better at cracking large seeds and some are better at cracking small seeds.

    From this you can infer that because the more adaptive (better suited) traits promote survival and reproduction (=success) - they must increase in frequency over the generations, and the less adaptive traits must decrease in frequency or disappear.

  5. In essence, natural selection is the physical and biological environment acting as a sorter of individuals - choosing which individuals possess the best adaptations for their current conditions. Therefore, a population will change over time. If the environment will switch again - over time - to reflect those changes. Natural selection is a highly localized event - because environments vary from region to region.

    Finally, a species cannont perceive or anticipate its needs for particular adaptations. Species (populations) are limited to using the adaptations that they were born with - just like the lone survivor with the suitcase. Once you survey the situation, you can't switch suitcases in mid-disaster.