remains a valid observation that the natural world at the dawn of the industrial age was characterized by highly diverse ecosystems and supported highly diverse human cultures. In the past few generations, however, as fundamental ecological changes have taken place, the world's heritage of natural and cultural diversity has been diminished.
These shifts have both caused, and been caused by, social changes. The world's collection of highly diverse cultural adaptations to local environmental conditions has begun to be replaced in many locations by a world culture dominated by very high levels of material consumption. Economic growth based on the conversion of fossil fuels to energy has greatly expanded international trade. Improved public health measures have spurred a rapid expansion of human numbers, requiring new approaches to resource management. These approaches have overwhelmed the conservation measures (formal or informal) of local communities, bringing overexploitation and poverty to many rural communities, and great wealth to cities and certain individuals, as urban elites in both industrial and developing countries control policies in such a way that primary productivity is very poorly rewarded.
Technological innovations have tended to promote exploitation of biological resources and to weaken traditional management systems, especially when a dominant group moves into a region occupied by technologically less advanced groups. The dominant society has the option of moving on to fresh resources when an area is exhausted, and it derives no particular advantage from adopting traditions of sustainable use. Its members are able to earn virtually all the immediate cash benefits of a forest, for example, but pay almost none of the long-term environmental costs. In addition, they capture a very small fraction of the potential cash benefits from the forest through short-term exploitation, rather than greater income from judicious long-term management in cooperation with local peoples.
At the same time, the subordinated groups lose any advantage from traditions of conservative use that might have been favored in times when they could exclude other groups from their territory. These traditions evolved when costs and benefits were internalized in the decisions made by communities, but as local peoples have had to assume the higher environmental costs of resource degradation, often their only rational response has been to join the exploiters in seeking greater benefits as well. This is the real tragedy of the commons: traditional management systems that were effective for thousands of years become obsolete in a few decades, replaced by systems of