Natural Selection

The Four Postulates1

  1. Individuals within species are variable.
  2. Some of these variations are passed on to offspring
  3. In every generation, more offspring are produced than can survive.
  4. The survival and reproduction of individuals is not random: The individuals that survive and go on to reproduce , or who reproduce the most, are those with the most favorable variations. They are naturally selected.

The "Modern Synthesis"

The Four Postulates1

  1. As the result of mutation creating new alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable in nearly all traits.
  2. Individuals pass their alleles on to their offspring intact.
  3. In most generations, more offspring are produced than can survive.
  4. The individuals that survive and go on to reproduce, or who reproduce the most, are those with the alleles or allelic combinations that best adapt them to their environment.

The outcome of the four postulates1

"...is that alleles associated with higher fitness increase in frequency from one generation to the next."


Reference:

  1. Freeman, Scott & Herron, Jon C. (2001) Evolutionary Analysis. New Jersey: Prentice-Hall