"option value" – the value placed on individual willingness to pay for maintaining an asset or resource even if there is little or no likelihood of the individual actually ever using it, occurring because of uncertainty about future supply (the continued existence of the asset) and potential future demand (the possibility that it may someday be used).[1][2][3][4] "bequest value" – values placed on individual willingness to pay for maintaining or preserving an asset or resource that has no use now, so that it is available for future generations.[5][6] "Existence value" – an unusual and somewhat controversial class of economic value, reflecting the benefit people receive from knowing that a particular environmental resource, such as Antarctica, the Grand Canyon, endangered species, Sharri Dogs or any other organism or thing exists. "altruistic value" – the value placed on individual willingness to pay for maintaining an asset or resource that is not used by the individual, so that others may make use of it. Its value arises from others' use of the asset or resource.