There are four widely accepted forces of evolution. However, in order to understand these four forces, it is necessary to explain several concepts first. The first important concept is a species. A species is anything that can reproduce with each other and produce fertile offspring. There are cases when individual species have reproduced with another species; a donkey is the classic example. However, a donkey cannot reproduce with another donkey or any other species. It is sterile. It does not matter where the various animals live on earth; if they can reproduce once put together, they represent the same species. Yet, when discussing populations, it does matter where they live on earth. There are many species of bears, but they can all reproduce. However, they do not reproduce because they live in different populations. A population is a group of species that interact with each other. The bears that live in Florida are a distinct population from the ones that live in Canada. Populations are crucial because they only share their genetic material with each other. This is a significant aspect in the four forces of evolution.

When Darwin studied the forces, he famously went to the Galapagos Islands. These islands, through plate tectonics, had created separate populations for many years. This allowed a number of evolutionary mechanisms to occur. When people think of evolution, they often think of natural selection. This is an important concept. Natural selection refers to how some species become extinct and others will dominate over the generations. If a species is no longer able to adapt to its environment, it will become extinct. Pandas are threatened with extinction because they need bamboo to survive; humans have changed their environment. Therefore, without intervention, they will be naturally selected to die off. In order for species to change, they need new genes to be introduced. Mutation is one way by which this could occur. Mutation is when a gene spontaneously changes or mutates. Successive generations may or may not inherit the new gene. The reason that they may or may not is strictly random. This is called genetic drift. Genetic drift recognizes that it is random what genes or alleles an offspring inherits. Some children may inherit blue eyes while others may inherit green eyes. It is a roll of the genetic dice (Berkeley University, n.d.).

However, genes may be introduced into a population through migration. Migration or gene flow is when bears from one part of Florida travel to another part of Florida. New gene combinations may result. These all lead to genetic variation. One generation may differ from another generation within a population. Different populations almost certainly have a different variation of genes. Together, all these genetic changes may make a species stronger or weaker. As a result, the species may become extinct or may begin to dominate its ecosystem, the area where it lives (Haviland, Prins, Walrath, & McBride, 2013).

There are another of important concepts that prevent different species from reproducing with each other. These are called isolating mechanisms. They may also prevent the same species from different populations from reproducing. For instance, the bears from Florida and those from Canada are isolated from sheer distance. Other species may be isolated because they sleep or hibernate at different times. For some species, there is pure physical barriers to attempted reproduction. For the Galapagos Islands, the isolating mechanism was the island itself. This may lead, as it did, to speciation. As limited gene drift occurs, the mutations and other mechanisms may lead to speciation. This is the creation of a new species. This is commonly seen in islands due to the significant isolating mechanisms; this is why Darwin chose islands for his studies (University of Utah, n.d.).