Darwin's Postulates



Charles Darwin (1809- 1882 A.D.), an English naturalist, was the most dominant figure among the biologists of the 19th century. He made an extensive study of nature for over 20 years and is known for his book Origin of Species. To explain the process of evolution by natural selection he broke it down into four simple postulates.


(1) The potential for a species to increase in number.

(2) The heritable genetic variation of individuals in a species due to mutation and sexual reproduction.

(3) Competition for limited resources.

(4) The proliferation of those organisms that are better able to survive and reproduce in the environment.


When food is abundant and growing conditions are favorable, a population has the potential to increase in number from generation to generation though sexual reproduction. This growth rate is exponential, however, exponential growth cannot continue indefinitely in a resource-limited environment. Eventually a population becomes so large that it runs out of free space, outgrows its food supply, or exhausts other assets. The upper limit on population density is called the environmental carrying capacity.


Trait differences are passed on from generation to generation through genes, as the biology textbook puts it, "tall parents tend to have tall offspring". This is probably the postulate we have covered the most in class. We looked at this topic from a mathematic perspective with punnet squares and statistics, from a chemistry perspective with nucleic acids and proteins, and from many other perspectives. After everything we saw and learned there is no doubt when it comes to inheritance. This explains why endemic species exist, why ethnicities tend to be clustered and why certain conditions are abundant in a family line.

Because we inherit our traits from two different organisms (mom & dad), we often look like a combination of both. However, there are some things that are out of our control like mutations in our genotype, which then result in changes in our phenotype. This too, adds to the variation in a certain species.


It is not hard to infer that there are unlimited wants and limited resources in the world, there is even a whole field of study for this: economics. Economics explains competition, but this is not exclusive to humans, competition for limited resources is inherent to every living organisms. Everyone has needs, even plants. Unfortunately, if certain needs are not met, it becomes a matter of life or death, this is where natural selection comes into play. Because of competition, only some get to live long enough to reproduce. The thing is, their offspring will have the traits needed to succeed in the competition for resources.


As I explained in the previous postulate, the genes of the organisms that thrive in a given environment are passed on in a higher frequency than the genes that do not tend to succeed, this is because the organisms that have the latter usually do not get to live long enough to reproduce and pass on their genes. This higher frequency, means a gene pool with with a higher percentage of traits that are advantageous to survive in the given environment. This is the basis of natural selection, now why is it called "natural", well because the environment is responsible for choosing the traits that will get passed on to the next generation.


Freeman, S., Allison, L., Black, M., Podgorski, G., Quillin, K., Monroe, J., & Taylor, E. (n.d.). Biological Science (5th ed.). Pearson.

Mayer, J. (n.d.). Population Dynamics. Retrieved April 06, 2016, from https://www.cals.ncsu.edu/course/ent425/library/tutorials/ecology/popn_dyn.html

Luskin, C. (2014, October 23). Natural Selection Struggles to Fix Advantageous Traits in Populations. Retrieved April 06, 2016, from http://www.evolutionnews.org/2014/10/natural_selecti_3090571.html

Pujari, S. (2014). 4 Main Theories of Evolution | Biology. Retrieved April 06, 2016, from http://www.yourarticlelibrary.com/biology/4-main-theories-of-evolution-explained-with-diagram-and-tables-biology/27220/