Natural, Relaxed, and Artificial
Selection
Hasan Mahmud
Natural Selection
• Is the basis of the other types of selection
• Competition
• Heriatble
Variation
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
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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.