(Copyright © 1999 Piero Scaruffi | Legal restrictions - Termini d'uso )
This monography is a rather technical account of how life could have
arisen on the Earth.
Morowitz' postulate is that life's definition is the definition of a living cell, and therefore he narrows down on the cell, and eukaryotes (multicellular organisms) in particular. Cells of eukaryotes have a membrane that separates the cell from the environment, and inside the membrane some organelles are contained. Morowitz' essay aims at explaining how this "partition" occurred and why it was so successful that it gave rise to the living kigndoms as we know them.
Morowitz argues against Monod's idea that life originated and evolved by chance. Morowitz has a different view. The fossil record shows that life occurred very early in the life of this planet, and then it spread very quickly: this seems to prove that life was a highly probable event, just about the opposite of what Monod claims.
Life is the property of an ecological system, not of a single, individual, isolated organism. An isolated living organism is an oxymoron. Life of any organism depends on a flow of energy, and, ultimately, life "is" that flow of energy. Morowitz has proven two theorems that analyze what happens during that flow of energy through the chemical systems that living organisms are made of: 1. those systems store energy in chemical bonds, i.e. their complexity steadily increases; and 2. those systems undergo chemical cycles of the kind that pervade the biosphere (e.g., the carbon cycle).
Morowitz first looks for the simplest living cell that can exhibit growth and replication and proves that, given the chemistry of life, it has to be a "bilayer vesicle" made of "amphiphiles" (a class of molecules, that includes, for example, fatty acids). Such a vesicle, thermodynamically speaking, represents a "local minimum" of free energy, and that means that it is a structure that emerges spontaneously. The bilayers spontaneously formed closed vesicles. The closure (the membrane) led to the physical and chemical separation of the organism from the environment. This, in Morowitz's mind, is the crucial event in the early evolution of life. Later, these vesicles may have incorporated enzymes as catalysts and all the other machinery of life. These vesicles are the "protocells" from which modern cells evolved.
I other words, Morowitz believes that first came membranes: first membranes arose, then RNA, DNA or proteins or something else originated life. First of all an organism has a border that differentiates it from the environment, that isolates it thermodynamically, that bestows it an identity, that enables metabolism. The second step is to survive: the membrane's content (the cell) must be able to interact with the environment in such a way that it persists. Then the cell can acquire RNA or DNA or whatever else and reproduce and evolve and so forth.