Natural, Relaxed, and Artificial Selection

Hasan Mahmud

Natural Selection

• Is the basis of the other types of selection• Competition Variation• Heriatble Difference in survival

• Relaxed and Artificial Selection are simply natural selection under different

• Each of the two change different parameters and

Relaxed Selection

• Is a selective phenomena that occurs when selective pressures are either elimated or dramatically reduced

• Are many new cases as society becomes more and more complex

Examples of Relaxed Selection

• When selective pressures are reduced or eliminated they can be biotic or abiotic

• Biotic examples – Predation elimination – Elimination of pathogen

• Abiotic examples– Changes in light and temperature and water– Changes soil and mineral composition

Modern Medicine

• Modern Medicine– Elimination of Many diseases that used to be

lethal– Compensation for Chronic and Genetic Diseases– Helps with common health problems• Sight problems• Hearing problems

Other Examples

• Malaria resistance– Without the pressure of possible infection there is

no heterozygous advantage• Galapagos – Without the presence of predators

and the abundance of food many animals in the Galapagos have become much larger than their main land counterparts

Problems with Relaxed Selection

• Many of the problems with relaxed selection only come into play when those pressures are re-introduced

• While some times the organism has come up with new way to deal with the pressures other times can be very costly to the pouplation

Artificial Selection

• Usually through intention human involvement the selection of non-essential traits in a population

• Many times the means through which selection is done is harmful to the population

• Artificial selection is done for two purposes– To increase production such as milk, eggs, meat– Enhancement of desired traits e.x dogs horses

Misconception of Artificial Selection

• Artificial Selection does and cannot create new traits

• Uses recessive traits or enhances existing traits to unusual expression

• Many of the artificially created species can still breed with ancestral species

Problems with Artificial Selection

• While some examples of artificial selection are not intentional – Initial domestication of Animals– Initial enhancement of crops

• Many examples of Artificial Selection are done through in breeding – Purebred dogs– Race horses

Connections

• Artificial, Relaxed, and Natural Selection are not separate and different forces

• Each is just a subset of the larger evolutionary force

• Artificial selection is taken to the extreme where there is a desired goal

• Relaxed selection is the absence of pressure and the evolutionary pathways that forms

Works Cited • http://images.google.com/imghp?gbv=2&um=1&hl=en&btnG=Search+Images• 1 Bryant, Edwin H. "Fitness Decline under Relaxed Selection in Captive Populations."

Conservation Biology 13 (2001): 665-69. • 2 "Evolution and Natural Selection." Evolution and Natural Selection. 10 Oct. 2008. Universtiy of

Michigan. 5 Nov. 2008 <http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html>.

• 3 Foster, Susan A., and John A. Endler. "Effects of Relaxed Selection Evolutionary Behavior." Geographic Variation in Behavior.

• 4 Gayle, Lisa. "Genetic Disorders." Encyclopedia of Childhood and Adolescence 42 (1998).• 5 Guyon, Isabelle. "An introduction to variable and feature selection." The Journal of Machine

Learning Research 3 (2003): 1157-182. • 6 Innan, Hideki. "Pattern of polymorphism after strong artificial selection in a domestication

event." Biological Science 109 (2004): 106667-0672. • 7 "Malaria and the Red Cell." 02 Apr. 2002. Information center for sickle and thalessis Disease. 28

Nov. 2008 <http://sickle.bwh.harvard.edu/index.html>.• 8 Robertson, A. "A Theory of Limits in Artifical Selection." Proceedings of the Royal Society of

London. Series B, Biological Sciences 153 (2000): 234-49.