Darwin's Four Postulates

Biology 12

Darwin’s four postulates are the simple criteria that explains the process of natural selection.

Natural Selection: The survival of the fittest. The individuals with certain heritable traits tend to produce more surviving offspring than the individuals without those traits.

1) Individual Variation

Individuals within species can vary in traits, such as size & shape.

E.g.) Finches in Galapagos island varies in its beak depth.

2) Inheritance of Variations

Some of these varieties of traits are passed onto offspring.

E.g.) Parents with deep beaks tend to have offspring with deep beaks, and parents with shallow beaks, offspring with shallow beaks.

3) In every generation, more offspring are produced than can survive

Because not all offspring can survive, the parents need to produce more offspring.

E.g.) Over 20 months, 84% of medium ground finches disappeared, due to the 1977 drought at Isla Daphne Major. Only fraction of finches, the most successful reproducing individuals, survived.

4) Survival and reproduction are not random

Individuals that survive and reproduce the most are those with the favorable variation. They are the selected individuals.

E.g.) After the drought, finches with deep beaks survived. In this new environment, they were the fittest. Because the average survivor had a deeper beak, the average beak size of the population changed.


Things to consider...

Evolution ≠ Natural Selection

Evolution = Descent with modification

Natural Selection = One of the mechanisms of evolution, as a result of adaptation



Florida International University. (2012). Darwinian natural selection [PDF file]. Retrieved April 4, 2016, from http://bioserv.fiu.edu/ortegaj/CHAPTER3_DARWIN_SPR.pdf

Freeman, S., Quillin, K., & Allison, L. (2013). Biological Science (5th ed.). San Francisco, CA: Benjamin Cummings.

University of California. (2002). Introduction to Ecological Genetics. Retrieved April 4, 2016, from http://ib.berkeley.edu/courses/ib162/Week1.htm