The sun, the moon and the stars would have disappeared long ago...had they happened to be within the reach of predatory human hands.
Havelock Ellis, The Dance of Life, 1923

Nature provides a free lunch, but only if we control our appetites.
William Ruckelshous

We abuse land because we regard it as commodity belonging to us. When we see land as community to which we belong, we may begin to use it with love and respect.
Aldo Leopold, A Sand Country Almanac

Don't blow it - good planets are hard to find.
Quoted in 'Time'