This definition is fairly broad and doesn't include the modern definition of evolution which includes several processes that produce and redistribute variation. They are as follows:
1). Increase Variation
•Mutation (a change in DNA; includes point mutation where changes occur in DNA bases, and/or in chromosome number or structure; Mutations are caused by radiation, harmful chemicals and replication errors. Though these are usually unfavorable in the present, they can be favorable in the long run, and because mutations are recessive, it can take a long time for them to become obvious or dominant within a population.)
•Recombination (exchange of genetic material between paired chromosomes during meiosis; crossing over; by itself, recombination doesn't change allele frequencies or cause evolution. It instead changes the composition of parts of chromosomes and can affect how some genes act.These changes can then be acted upon by natural selection. Natural selection is defined as genetic changes of certain traits due to biological variation.)
•Gene flow (exchange of genes between populations; occurs because people move among populations, which increases the variation and reduces the difference between two populations)
2). Decrease Variation
•Genetic Drift/Founder Effect (Results when a small population is involved; made by random factors in small populations. The Founder Effect is a type of genetic drift where allele frequencies are altered in small populations that are taken from or are remnants of large populations. This isolation could lead to this species becoming so different or "drifting" so far that they are no longer able to mate with anyone that is not inside of their small population. It also operates on the idea that humans don't reproduce alleles in the same proportions that they receive them. This results in some alleles being passed on while others aren't. This phenomenon is up to chance and causes allele frequencies to randomly fluctuate from generation to generation.)
•Non-random Mating (Humans select their mates based on some type of criteria. Major histocompatibility complex or MHC plays a major part in this. The basic idea is that these genes detect favorable odors, the most favorable odors being those that come from individuals whose DNA is the most different from your own. {1} The long-term effect here is the alteration of gene frequency. Humans either marry within a group, whether it be social class, culture, religion, gender or race. This is known as endogamy and results in genetic drift. Exogamy, which is marrying outside of a group, results in gene flow.
Examples:
During the Industrial Revolution, the pollution caused trees to turn a darker color. In response to this environmental change, light colored moths also began to change color, becoming darker-colored to blend in with the trees for protection from birds. The ones that remained light-colored died off because they were easy targets for the birds, leaving the darker-colored ones safe.
Another example of evolution is seen in domesticated animals. Darwin focused on domestication because he believed it gave rise to more variation. He believed that this was mostly because of their environment. The best example of this is the morphology of the dog from the wolf. Darwin also noted that all domesticated animals tended to evolve in the same direction.we see this primarily in animals response to humans, namely in their loss of the "species-specific wild-animal behavorial response to humans." {2} We also see variation in body size, body shape and hair type.
Resources:
{1} http://m.rspb.royalsocietypublishing.org/content/275/1652/2715.long
{2} http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763232/
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