Darwin's Four Postulates
The Origin of Species
Postulate #1
In All Species There Is Heritable Variation
Darwin argued that every single thing in the planet derived its genotype from that of those who procreated it. Then why is no offspring an exact clone of the parents? While the offspring may possess different genes for different traits, only some of these are expressed, depending on whether they are dominant or recessive. The large variety of genes present in a population that is not isolated makes it impossible for a child to be exactly the same as the parents.
Postulate #2
More Progeny Are Produced Than Can Survive
This postulate is directly related to Darwin's idea of Natural Selection, the means through which species evolved. Certainly, every generation of a specific species will contain more than one offspring; in some cases, they will contain a myriad of them, each with a different traits. Nevertheless, not all of them will possess the traits that are necessary for surviving the conditions that are present in the environment to which they are introduced. These conditions may range from the harshness of climatic conditions, to overall accessibility to food sources, to deadly predators, to epidemic viruses. Only the individuals that possess traits that enable them to cope with these conditions will grow and procreate.
Polar Bears
Their fur by itself allows them to survive in the cold weather, but they must also acquire other abilities, such as swimming and climbing, in order to do so.
Antelopes
They are exposed to one of the quickest predators alive. If they are quick enough, they will survive, but it is not uncommon for them to be ultimately preyed on.
Mating
Darwin believed that the organisms that exhibited the most "desirable" qualities would be those that ultimately mated and procreated.
Postulate #3
Survival And Reproduction of Individuals Is Not Random
This postulate extends the idea expressed in the previous one. Darwin argued that species do not survive and, furthermore, procreate arbitrarily - their survival is based on their possession of traits that enable them to cope with the conditions of the environment in which they are found. Naturally, because the "fittest" survive, they will eventually mate and produce offspring that possess the genes and express some of the traits that allowed for the survival of the parental generation.
Camouflage
One of the many mechanisms that are seen throughout the Animal Kingdom.
Poisonous Frog
These animals release toxic chemicals that are extremely harmful to anyone that touches them, humans included.
Cobra
Snakes like this may seem defenceless and puny... but looks are truly deceiving.
Postulate #4
More Fit Phenotypes Are Present In Subsequent Generations
Every species that exists today is an example of this final postulate. Had we not acquired distinct traits that made us more capable of dwelling in this planet, we would not exist in our present state. Human beings are fascinating in the sense that they developed organs that allowed them to manipulate the world almost to their liking, such as brains and hands with opposable thumbs. However, we are not the only example of "fit" phenotypes. Throughout the rest of the animal kingdom, we find a plethora of species whose phenotypes reflect fascinating features and mechanisms that enable them to fight threats, such as camouflage and body poison. But even in the simplest things, from beak shape to neck size, the traces of evolution and natural selection are evident in all living things. We are the product of an incredible process that has been taking place for millions of years - and that will surely keep on going for eternity.
Giraffes
Developed long necks to reach food and be on the lookout for predators.
Snow Leopards
Their fur makes them almost invisible in the snowy mountains where they are found.
Flying Squirrels
They can jump from tree to tree by gliding, gracefully escaping from predators.
Sources
Buffalo State University. (n.d.). Chapter 3: Darwinian Natural Selection. Retrieved April 7, 2015, from:
http://faculty.buffalostate.edu/penaloj/bio405/outline3.html
Evansville University. (n.d.). Natural Selection. Retrieved April 7, 2015, from:
http://faculty.evansville.edu/de3/b32003/lecture%20summaries/selection.pdf
http://ib.berkeley.edu/courses/ib162/Week1.htm
University of Georgia. (n.d.). Natural Selection. Retrieved April 7, 2015, from:
http://wallace.genetics.uga.edu/groups/evol3000/wiki/d0776/Natural_Selection.html
University of Michigan. (2010, October 10). Evolution and Natural Selection. Retrieved April 7, 2015, from:
http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html