intense selection in the opposing direction. We strongly encourage those responsible for managing harvested wild populations to take into account possible selective effects of harvest management and to implement monitoring programs to detect exploitation-induced selection before it seriously impacts viability.
Humans have exploited wild populations of animals for food, clothing, and tools since the origin of hominids. Human harvest of wild populations is almost always nonrandom. That is, individuals of certain size, morphology, or behavior are more likely than others to be removed from the population by harvesting. Such selective removal will bring about genetic change in harvested populations if the selected phenotype has at least a partial genetic basis (Table 7.1). For example, the frequency of elephants (Loxodonta africana) without tusks increased from 10% to 38% in South Luangwa National Park, Zambia, apparently brought about by poaching of elephants for their ivory (Jachmann et al., 1995). Similarly, trophy hunting for bighorn sheep (Ovis canadensis) in Alberta, Canada, caused a decrease in horn size because rams with larger horns had a greater probability of being removed from the population by hunting (Coltman et al., 2003). It has also been suggested that the greater difficulty of catching introduced brown trout (Salmo trutta) than native North American species of trout is the result of angling for brown trout in Europe for hundreds of years before their introduction to North America (Miller, 1957). Moreover, harvest need not be selective to cause genetic change; uniformly increasing mortality independent of phenotype will select for earlier maturation (Law, 2007).
In agriculture, the practice for thousands of years has been to use the most productive animals (and plants) as breeding stock, with the goal of increasing the frequency of desirable phenotypes. Aquaculture has adopted similar objectives over its shorter history (Gjedrem, 2005). In contrast, the opposite has been true in the exploitation of wild animal populations. The most desirable individuals have been harvested, leaving behind the less desirable to reproduce and contribute genes to future generations. Therefore, harvest of wild populations has tended to increase the frequency of less desirable phenotypes in wild populations.
There has been surprisingly little consideration of human-induced selection in the wild until recently [reviewed in Allendorf et al. (2008)]. Even more surprising perhaps is the absence of any detailed consideration of this effect by Darwin because he had such a passion for hunting as a young man. In several places, Darwin commented on the lack of wildness of birds on islands where they have not been hunted by humans (Darwin, 1958b, p. 231; 1962, p. 400). In his lengthy consideration of “Selection by