There are four basic causes of forces of evolution. These four forces are mutation, gene flow, genetic drift, and natural selection. Together, these forces help to change species over time into new species. The development of new species is called speciation. In order to discuss evolution, it is important to understand the various terms associated with evolution. The term species can only be properly applied to a life form that can successfully reproduce with each other. Successful reproduction is defined as the ability of the offspring to reproduce themselves. If offspring are sterile, it is not considered successful offspring. For this reason, mules, which are the product of two completely different species, are not considered successful offspring. They cannot reproduce. Two empire penguins, both the same species, can reproduce successfully. They are therefore considered the same from a genus and species aspect.
Species change over time. This is called speciation, when a new species develops from former species. Sometimes species develop into something that is no longer suitable to the environment. It will then become extinct. However, often species develop in methods that help them to interact with the environment in a more successful way. In this way, the species is likely to thrive. This force, that allows species to change over time and increase or decrease the survivability of the species is called natural selection. Nature selects what species will survive. If the environment changes, as we are witnessing with climate change, the species must adapt in future generations to survive with the changes. How species change is the result of a number of other factors though.

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Mutations are one way that species change. Mutations are random. There is no way to control mutations in the DNA. DNA is the “blueprint” of all living things. All offspring contain some of the original DNA of the parent. However, parents may pass down different DNA for specific genes because of changes in the DNA structure. Therefore, the offspring now possess genes that were not found in nature before the mutation (Larsen, 2010).

Gene flow also helps to create changes in evolution. Gene flow refers to a population. A population is a group of species that interact with each other. A group of polar bears in Canada is one population, while a group of polar bears in Norway is another population. They share genes among the population. If a polar bear from Canada travels to Norway and reproduces, it has added new genes to that population. This is gene flow. When populations remain isolated and do not have any new genetic material, they may develop into another species. They pass down isolated genes, and recessive genes may occur. This occurs in humans as well. The Amish do not tend to marry outside their small population. Therefore, they have a number of recessive diseases due to the lack of gene flow.

Genetic drift represents that long-term changes in the DNA of a species due to the “luck” of some members to reproduce. Oftentimes, the healthy or the members who are best suited to the environment reproduce successfully, and produce healthy offspring. This helps strengthen the species. However, it is important to recognize that luck is sometimes just as important. If an animal is killed by a hunter, the animal can no longer pass down its DNA. Overtime, only some of the members of the population will pass on the DNA. The DNA may change over generations as a result of this (Encyclopedia Britannica, 2017).

Mutation, natural selection, gene flow, and genetic drift are responsible for the wide number of species alive today. They are also partially responsible for the large number of species that are now extinct. It is important to recognize that now all extinctions are the result of evolutionary forces. Extinctions may be the result of a sudden, cataclysmic event, such as a meteor, or because of environmental changes, such as the damage humans do to the environment.

  • Encyclopedia Britannica. (2017). Genetic drift. Retrieved from:
  • Larsen, C. (2010). Genes and their evolution. Retrieved from: