Evidence from artificial selection


Artificial selection demonstrates the diversity that can exist among organisms that share a relatively recent common ancestor. In artificial selection, one species is bred selectively at each generation, allowing only those organisms that exhibit desired characteristics to reproduce. These characteristics become increasingly well developed in successive generations. Artificial selection was successful long before science discovered the genetic basis. Examples of artificial selection would be dog breeding, genetically modified food, flower breeding, cultivation of foods such as wild cabbage, and others.

Overview


Artificial selection (or selective breeding) describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive ability (“Darwinian fitness”). As opposed to artificial selection, in which humans favor specific traits, in natural selection the environment acts as a sieve through which only certain variations can pass.

The deliberate exploitation of artificial selection has become very common in experimental biology, as well as the discovery and invention of new drugs. Artificial selection can also be unintentional; it is thought that domestication of crops by early humans was largely unintentional.

Contrast to natural selection


There is no real difference in the genetic processes underlying artificial and natural selection, and the concept of artificial selection was used by Charles Darwin as an illustration of the wider process of natural selection. The selection process is termed "artificial" when human preferences or influences have a significant effect on the evolution of a particular population or species. Indeed, many evolutionary biologists view domestication as a type of natural selection and adaptive change that occurs as organisms are brought under the control of human beings.

However, it is useful to distinguish between artificial selection that is unintentional or involves manipulating the environment only, and artificial selection that alter internal DNA sequences in the laboratory. Genetic manipulation in labs can be used to produce the same changes that could be attained by selective breeding faster by Cisgenesis. However, other changes such as Transgenesis introduce DNA into an organism that is not available in the species' gene pool.

Laboratory usage


The deliberate exploitation of selective power has become common in experimental biology, particularly in microbiology and genetics. In a ubiquitous laboratory technique in genetic engineering, genes are introduced into cells in cell culture, usually bacteria, on a small circular DNA molecule called a plasmid in a process called transfection. The gene of interest is accompanied on the plasmid by a reporter gene, or "selectable marker", which encodes a specific trait such as antibiotic resistance or ability to grow in high salt concentrations. The cells can then be cultured in an environment that would kill normal cells, but is hospitable to those that have taken up and expressed the genes on the plasmid. In this way expression of the reporter gene serves as a signal that the gene of interest is also being expressed in the cells.

Another technique used in drug development uses an iterative selective process called in vitro selection to evolve aptamers, or nucleic acid fragments capable of binding specific organic compounds with high binding affinity.

Studies in evolutionary physiology, behavioral genetics, and other areas of organismal biology have also made use of deliberate artificial selection, though longer generation times and greater difficulty in breeding can make such projects challenging in vertebrates.


Sources

Artificial Selection PowerPoint, University of Wisconsin-Madison

Buffum, Burt C. Arid Agriculture; A Hand-Book for the Western Farmer and Stockman, p. 232. Accessed at [1], June 20, 2010.

Lush, Jay L. Animal Breeding Plans, p. 21. Accessed at [2], June 20, 2010.

Jan Z. Wilczynski (December 1959), "On the Presumed Darwinism of Alberuni Eight Hundred Years before Darwin", Isis 50 (4): 459–466 [459–61], doi:10.1086/348801

Darwin 1859, p. [3]

Darwin 1859, pp. 197–198

Swallow JG, Garland T, Jr. (2005). Selection experiments as a tool in evolutionary and comparative physiology: insights into complex traits—an introduction to the symposium. Integr Comp Biol, 45:387–390.PDF

Garland T, Jr. (2003). Selection experiments: an under-utilized tool in biomechanics and organismal biology. Ch.3, Vertebrate Biomechanics and Evolution ed. Bels VL, Gasc JP, Casinos A. PDF

Garland T, Jr., Rose MR, eds. (2009). Experimental Evolution: Concepts, Methods, and Applications of Selection Experiments. University of California Press, Berkeley, California.

via Wikipedia