Namibia has a long history of protecting its environment and its wildlife. It is one of just a few nations in the world that expressly includes principles of conservation in its Constitution, requiring the adoption of policies aimed at maintaining biological diversity and utilising "natural resources on a sustainable basis for the benefit of all Namibians, both present and future." Namibia’s Nature Conservation Ordinance (NCO), one of the nation's principal legislation regarding environmental conservation and wildlife crime prevention, has been in force for over 40 years. After Namibia's poaching problem of the 1970s and 1980s, the population rates for the nation's two most vulnerable species, the Black Rhinoceros and the African Elephant, largely recovered during the 1990s and 2000s. However, the number of poaching incidents in Namibia has increased at a staggering rate in the past 6 years. In the context of the entire black rhino population, these numbers are even more alarming - it is estimated that a mere 5,000 remain in the wild, approximately 1,850 of which live in Namibia. Elephants and rhinoceroses are especially at risk of poaching due to the value of their tusks and horns, but other animals are increasingly in danger as well. For example, lion and giraffe bones are also being used in illegal wildlife trade. Pangolins - mammals that are often called "scaly anteaters" and that also live in Namibia - are also being increasingly trafficked for their scales and meat, and for use in Chinese medicinal products. Indeed, the pangolin is the most trafficked mammal in the world.