"As a jarring illustration of our tendency to value the human side over the prerequisite physical/ecological side, imagine that somehow we manage to emerge from the coming centuries having established a truly sustainable existence. All resources are renewed by nature at the rate of extraction for human needs; population is steady and at a level just tolerable to the planet in terms of indefinite support. Diverse ecosystems are left to thrive in their natural states. But imagine that we are still plagued by cancer and other maladies, so that life expectancy is, say, 90 years. Then what if a team of researchers hits on a cure for (most forms of) cancer? Hurray! At last! Unambiguously good, right? Well, not so fast. All other elements held the same, longer life spans translate to a higher population, putting additional resource burdens on the planet that it cannot handle in the long term. In order to adopt and implement the cure for cancer, we would have to either deliberately reduce population or lower the standard of living to accommodate the change. All other considerations of the complex society about economic impacts, equity of distribution, legal and political facets, or interaction with religious belief systems must take a back seat to the most fundamental and important question: is this change physically viable on this finite planet in the long term?"