Biological evolution is simply heritable change through time. It is important to understand because it lays the foundation to understanding all of biology, including health sciences.
Genetic Variation
Without genetic variation, the basic mechanism of evolutionary change could not operate. The three primary sources of genetic variation are mutations, gene flow, and nonrandom mating (University of California, Berkeley, 2007). First, mutations are random changes in the DNA of an individual. The environment may have an effect of the rate of mutations but does not generally influence the direction of the mutation. This can be seen in the Lederberg Experiment which showed that certain bacteria had a resistance to penicillin before the bacteria was ever exposed to the antibiotic (University of California, 2007). There are several ways mutations can occur, but the two main causes are when DNA fails to replicate properly and when external influences (chemicals or radiation) damage DNA.
The second factor relating to genetic variation is gene flow. Gene flow is the movement of genes from one population to another. Examples of gene flow range from pollen being transported from flower to flower by insects to people moving from city to city (University of California, 2007). It is reasonable to assume that species that are inactive have a lower rate of gene flow between populations while species that are active have a higher rate of gene flow (Scott, 2004). Gene flow is important within evolution because it can introduce or reintroduce a gene within the population, which increases the genetic variation of the population (University of California, 2007). It also can make two distant populations genetically similar or it can cause speciation between populations.
The last component of genetic variation is nonrandom mating. Nonrandom mating results with some individuals within a population having a greater opportunity to mate than others because of easily observable traits that are regulated by cultural and social values (University of California, 2007). Random mating is very unlikely to occur in nature for several reasons. One reason is that it just easier to mate with an individual that is close than one that is far away. Nonrandom mating guarantees that certain desirable genes are passed along to the next generation while undesirable ones die out.
Genetic Drift
Genetic variation is a crucial part of evolutionary change, but its counterpart genetic drift is another important factor for keeping the evolutionary train running. Genetic drift is when some individuals leave behind more descendents than others thus passing along a few more genes to the next generation purely by chance (University of California, 2007). This process is entirely random and does not work to produce adaptations.
Natural Selection
Natural selection is probably the least understood mechanism of evolution. It is the process that allows favorable traits that are heritable to become more common in future generations (Scott, 2004). One of the most popular examples is the Galapagos finches which have evolved strong, thick beaks to break tougher seeds during droughts. Fitness is the measure of how successful an organism is when passing along their DNA. For example if the survival rate for pink spotted frogs is low, but the survival rate for green spotted frogs are high, one could say that the green spotted frogs have a higher fitness than pink spotted frogs. Adaptation is a feature that has evolved through natural seletion. Adaptations can range from behaviors that ward off predators to increased ear size to regulate the body temperature like elephants.
Work Cited:
- Misconceptions of Evolution. (2006). http://evolution.berkeley.edu/evosite.
- The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California. Accessed on November 10, 2007.
- Scott, E. C.(2004). Evolution Vs. Creationism An Introduction. London: University Of California Press.
Written by Erika Storbeck and Rebecca M. Price