Postulates

Descent with modification

  1. all life evolved from one or a few simple kinds of organisms
  2. each species, extinct or extant, arose from another species that proceeded it in time
  3. evolutionary changes were gradual and of long duration
  4. new genera, families, orders, classes and phyla arose by the kind of evolution that produced new species
  5. new genera, families, orders, classes and phyla arose by the kind of evolution that produced new species
  6. \
  7. The greater the similarity between 2 groups of organisms, the closer is their relationship and the closer in geologic time is their common ancestral group
  8. Extinction of old forms (species) is a consequence of the production of new forms or environmental change
  9. once a species or other group has become extinct it never reappears
    1. evolution continues today in generally the same manner as during geologic eras
    2. the geologic record is very incomplete

The Theory of Natural Selection

  1. a population of organisms has the tendency and the potential to increase at a geometric rate
  2. in the short run the number of individuals in a populations remains fairly constant
  3. the conditions of life are limited
  4. the environments of most organisms have been in constant change throughout geologic time
  5. only a fraction of the offspring in a population will live to produce offspring
  6. individuals in a population are not all the same: some have heritable variations
  7. life activities (“struggle for existence”) determine which traits are favorable or unfavorable by determining the success of the individuals who possess the traits
  8. individuals having favorable traits (favorable variations) will, on the average, produce more offspring and these with unfavorable traits will produce fewer offspring
  9. natural selection causes the accumulation of new variations and the loss of unfavorable variations to the extent that a new species may arise