Having discussed the systems view of life in its biological dimension (Chapters 7–11), its cognitive dimension (Chapters 12–13), and its social dimension (Chapter 14), and having proposed a conceptual framework that integrates these three dimensions (Section 14.3), we shall now, in the last part of our book, include the ecological dimension in our synthesis of the systemic conception of life.

In fact, we could have (and, perhaps, should have) begun this discussion with the ecological dimension, since it is well known that no individual organism can exist in isolation. Animals depend on the photosynthesis of plants for their energy needs; plants depend on the CO2 produced by animals, as well as on the nitrogen fixed by microorganisms at their roots; and together plants, animals, and microorganisms regulate the entire biosphere and maintain the conditions conducive to life. As Harold Morowitz (1992, p. 54) reminds us,

Indeed, according to Gaia theory (discussed in Section 8.3.3), the evolution of the first living organisms went hand in hand with the transformation of the planetary surface from an inorganic environment to the self-regulating biosphere. “In that sense,” writes Morowitz (1992, p. 6), “life is a property of planets rather than of individual organisms.”