A pattern of small, random deviations between sides in the size of a given trait -the random component of bilateral asymmetry, i.e., subtle random deviations from perfect bilateral symmetry. It arises when genetic or environmental stressors disrupt developmental processes that normally promote symmetrical growth. Fluctuating asymmetry is of particular interest because of its potential as a biomonitor of environmental quality. It is a relatively new tool for assessing the impact of environmental and genetic stresses on populations. One of the main advantages of FA is its increased sensitivity relative to other bioindicators. If effective, this tool could allow biologists to monitor populations and make recommendations before a severe problem arises, often without the high cost of other solutions.