Darwin's Four Postulates
1.Variation Among Individuals Within Species.
One of Darwin's postulates is of course variations in individuals. This variations which are sometimes hereditary are what allow survival of the fittest to work. The individuals with the the most useful traits are the ones that survive.
An example of this is the finches Darwin observed they are all part of the same species but each of them have individual traits that allow them to survive on their own environment.
2. Some of the variation is heritable
As I explained briefly above the the characteristics that helps the organism survive the most will most like be passed down. This process is what allows the organism to keep evolving, but it of course takes millions of years.
An example of this is that humans have come to alter is dog breeding. Humans have taken a wild animals and over the course of hundreds of years molded into different shapes and sizes depending on the traits they want to see passed on.
3.In every generation, more offspring a reproduced than can survive.
Nature is full of probability and odds, this is why organisms will reproduce more than necessary this increases the chances of a stronger organisms and speed up the process of natural selection, with only the fittests of the offspring being able to survive.
An example of this would be the turtles people like to see hatch on the beach. This turtles were left there and buried by their mother but nature is not forgiving. Most of the turtles won't make it to the ocean, they will get eaten by predators or get stepped on before they hatch. Only the fastests and sneakiest will make it and survive.
Non-random survival and reproduction
Nature does not choose who survives on who is the fluffiest or cutest, and the process is not random either. The organisms that survive are strongest, fastest, or sometimes the ones that hide the best.
An example of his us, humans. Only the smartest and strongest used to survive leading to the Homo sapien sapiens and the extension of our predecessor the Homo sapiens.
B. (n.d.). Introduction to Ecological Genetics. Retrieved April 08, 2016, from http://ib.berkeley.edu/courses/ib162/Week1.htm
B. S. (n.d.). Ch 3. Darwinian Natural Selection. Retrieved April 08, 2016, from http://faculty.buffalostate.edu/penaloj/bio405/outline3.html
L. N. (2012). Darwin’s Theory of Evolution. Retrieved April 08, 2016, from http://www.science4all.org/article/darwins-theory-of-evolution/