If we are to exercise our responsibilities so that all life can continue on earth, they must have a moral and philosophical basis. Simple self-interest, economic profit and absolute materialism are no longer enough... It has been made perfectly clear that a concern for any part of life on this planet — human, plant or animal, wild or tame — is a concern for all life. A threat to any part of the environment is a threat to the whole environment, but we must have a basis of assessment of these threats, not so that we can establish a priority of fears, but so that we can make a positive contribution to improvement and ultimate survival.

The Environmental Revolution: Speeches on Conservation, 1962–77 (1978)