Ecological Structures
Life and the Earth's Environment
What is Life?
Materials for Life
Capturing Energy for Life
Evolution & the Environment
Disruptive Forces on Ecosystems
Measurement of Impact on Ecosystems
Sustainability & Ecological Integrity
Approaches to the Natural Environment
Global and Regional Scales
Global Agreements
Philosophies for Sustainability
Internet Links
Other Resources
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Ecological System
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What is Life?

"Life is not an inherent property of matter. Life is indeed associated with matter, but it appears only under very specific conditions and, when it does, it expresses itself in very diverse and individual ways...We shall come closest to understanding the principle of life if we can discover the principles according to which life could begin...How life did begin, however, can only be understood by appeal to historical evidence."
  -- Manfred Eigen 1

"Being alive is being sensitive to specific cues in the environment, to transduce and amplify minute signals into definite actions. Being alive is to achieve the long-range coordination of astronomical numbers of submicroscopic, molecular reactions over macroscopic distances. It is to be able to summon energy at will and engage in extremely rapid and efficient energy transduction"
  -- Mae-Wan Ho 2

What is special about living systems and their relationship to the environment? In this unit, we seek to understand some of the organizing principles of living systems, recognizing with humility what Manfred Eigen and Mae-Wan Ho say--that we can only understand what happened, not why it did.

Reflection on the nature of life even for a short while brings to mind the awesome variety, coherence, and organization in the functioning of live organisms. Exchange of materials with the environment and adaptation to environment are also evident. While we can try to understand these interactions, and guess at how life might have evolved on Earth, we can only guess at how life did begin and survive. In the words of the Nobel Laureate Manfred Eigen, "life is historical reality."


[1] Eigen, Manfred. Steps Towards Life: A Perspective on Evolution.

[2] Mae-Wan Ho. The Rainbow and the Worm, Singapore: World Scientific Publications, 1994. p. 10



  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.