allowable to reduce the natural resource stock for an increase in the stock of knowledge. According to Locke's principle, each generation should leave "enough and as good for others" that follow on. Apart from the imprecision of this rule, this raises the question of whether there should be 'betterment' for future generations. If incomes are low and poor socio-economic conditions prevail, economic 'betterment' of future generations would seem appropriate. If economic growth or development did not occur in a very poor society, living in some sort of a stationary state with nature, income might be sustainable. However, the society might be vulnerable to natural disasters, to some extent at the mercy of nature and the prevailing economic conditions may be undesirable, a situation facing our ancestors in the past. What one needs to attain and sustain is a satisfactory standard of living. Once this is achieved there, is no reason why future generations should have a higher one. In order to achieve a minimum satisfa ctory standard of living in society, it is likely to be necessary to deplete natural resource stocks and in some cases reduce biodiversity, e.g., eliminate populations of slow growing species, in order to generate sufficient surplus income to enable additions to the stock of knowledge to be made. However, as biodiversity declines, the marginal opportunity cost of removing more diversity is likely to increase and do so at an increasing rate. At the same time uncertainty about the impact of eliminating further species may spiral. Therefore, the importance of applying the precautionary principle and conserving biodiversity may increase because the· economic value of retaining remaining options may rise. Consequently, the application of safety- oriented rules such as the safe minimum standard approach to species conservation may attain increasing support.