At the heart of Locke's system of intergenerational ethics is a concern for preservation of the human species. That is the primary and fundamental law which is the standard and measure of all the other natural laws depending from it; f64 it is referenced at least eight times in the Second Treatise of Government.f65 Of course, the principle has many more direct applications today than it did in Locke's time. In the 17th century, it would have been difficult to conceive of any action or set of actions which could entirely eliminate humanity. Today we can imagine such scenarios all too easily, the most obvious ones involving nuclear or biological war, or global climate change.
Locke adheres closely to the biblical notion that the earth exists for humankind as a sort of intergenerational commons. He cites King David for the proposition that "God gave the world to Adam and his posterity in common."f66 This notion, taken literally, fixes all landed property interests as varying species of tenancy or trust. Of course, one of a tenant's chief obligations is to maintain property in as good and useful a condition as it was originally received. f67 Accordingly each generation, as tenant, is expected to steward the earth for both the landlord (God) and later tenant-generations. Scott Gerber paraphrases Locke aptly: "Every individual is acting as a trustee of his Creator's property, with the purpose of the trust being the preservation of mankind." f68 As noted above,f69 the use of the landlord tenant analogy to describe intergenerational relations was anything but new by Locke's time. The metaphor was destined to become standard fare among the founders and their contemporaries.
A natural corollary to the "world as commons" idea is Locke's absolute prohibition against waste
and destruction. If all our possessions are but temporary gifts from the Creator, then we obviously have an
obligation to exercise due care in our custody of those possessions. "Nothing was made by God for man to
spoil or destroy." f70
Locke applies this prohibition in a variety of ways. For instance, an individual in the state of nature who claims a property interest in particular fruits of nature is bound to use or consume the claimed fruits before they spoil, "else he took more than his share and robbed others." f71 While this prohibition of waste or spoilage could be understood simplistically as no more than a mandate for resource development, f72 there is more to it than that. In paragraph 6 of the Second Treatise, Locke identifies preservation as an affirmative value to be weighed alongside other values and property interests: