Everything about Stabilizing Selection totally explained
Stabilizing selection, also referred to as
purifying selection or
ambidirectional selection, is a type of
natural selection in which
genetic diversity decreases as the
population stabilizes on a particular
trait 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.
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.
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