Stabilizing selection

Stabilizing selection

value. Put another way, extreme values of the character are selected against. This is probably the most common mechanism of action for natural selection.

A classic example of this is human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis. However, the recent improvements in human nutrition in developed countries has led to rising rates of caesarean sections, since babies are routinely out-growing the female reproductive tract. [cite journal |author=Liston WA |title=Rising caesarean section rates: can evolution and ecology explain some of the difficulties of modern childbirth? |journal=Journal of the Royal Society of Medicine |volume=96 |issue=11 |pages=559–61 |year=2003 |pmid=14594971 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=14594971 |doi=10.1258/jrsm.96.11.559]

Stabilizing selection operates most of the time in most populations. This type of selection acts to prevent divergence of form and function. In this way, the anatomy of some organisms, such as sharks and ferns, has remained largely unchanged for millions of years.

Stabilizing selection can sometimes be detected by measuring the fitness of the range of different phenotypes by various direct measures, but it can also be detected by a variety of tests of molecular sequence data, such as Ka/Ks ratios, changes in allele frequency distributions, and the McDonald Kreitman test. [cite journal |author=Sheets HD, Mitchell CE |title=Why the null matters: statistical tests, random walks and evolution |journal=Genetica |volume=112-113 |issue= |pages=105–25 |year=2001 |pmid=11838761 |doi=10.1023/A:1013308409951] [cite journal |author=McDonald JH, Kreitman M |title=Adaptive protein evolution at the Adh locus in Drosophila |journal=Nature |volume=351 |issue=6328 |pages=652–4 |year=1991 |pmid=1904993 |doi=10.1038/351652a0]

ee also

*Directional selection
*Disruptive selection
*Koinophilia

References


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