Scientists have agreed upon the four forces of evolution, the basics of the evolutionary process. Natural selection is the first of these, wherein the creature with the best adaptation to its environment will not necessarily produce more offspring than another within the same environment, but will have a higher survivability, thus working to continue to spread the adaptation. Genetic drift is the next force of evolution, a random process which plays a factor in determining the gene variants that survive. The third of these forces is gene flow, or gene migration, which occurs when genes are transported from one population to another, as is the case when pollen from genetically modified plants affects and fertilizes a non-genetically enhanced variant of the same plant. The fourth force of evolution is mutation, a random change to the DNA of an organism which may impact everything from its most basic physiology to how it appears to how it behaves, for an extreme example of mutagenic properties, a look to the X-men describes this particular aspect very well.
Population is the standard unit used when speaking of evolution; it has to do not with a species as a whole, unless macro evolution comes into play, but rather looks at the changes within a population, or a group of organisms, in a specific area. Looking at the same species within two different areas, two different populations of the same species, in other words, each of these two populations may work to evolve in completely different ways, providing inherent changes in appearance and in behavior as a result of the area in which they reside.
Genetic variation plays another factor, for without it, some of the most basic mechanisms of evolution could not occur. Genetic variation has to do with mutations, the flow of the genes, and sex. One mutation does not typically make a difference, more accurately it takes a group of mutations in gene structure to result in a drastic, visible change; sex introduces new genes into the mix, and gene flow allows for the transportation of genes from one population to another. These three different aspects make up the overall concept of gene variation, proving the necessity of this particular factor in the evolutionary process.
Isolating mechanisms serve to prevent two different species from being able to reproduce with each other, and come in two different types, prezygotic isolating mechanisms and postzygotic isolating mechanisms. Prezygotic isolating mechanisms work to ensure that the egg and sperm of two different species may not produce a fertilized egg and are comprised of six different aspects including geographic isolatin, habitat isolation, temporal isolation, behavioral isolation, mechanical isolation and physiological isolation. Postzygotic isolating mechanisms consist of hybrid mortality, hybrid sterility and hybrid inferiority; in other words, the hybrid is more likely to die, be sterile (as with a mule), and be inferior to the two organisms that created it.
Speciation occurs when the genetic changes that occur within a population are large enough that one set may no longer reproduce with another set, essentially and effectively creating two different and distinct species. These evolutionary processes are occurring each and every day and serve to provide a fascinating background for the world at large. Through an understanding of these changes, it is possible to understand evolution as a whole.