(Copyright © 2000 Piero Scaruffi | Legal restrictions - Termini d'uso )
DeDuve provides a detailed and fascinating history of life on the earth, how it "emerged" and how it developed, from the first catalysts of life all the way down to the mind.
His excursion covers the origin of life, genes, cells, evolution, brain, consciousness.
Life started with the spontaneous formation of organic molecules which are widely available in the universe. Organic matter is made of a combination of carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur (the "CHNOPS" principle). The prebiotic conditions of the Earth enabled them to grow in a recursive relationship which eventually gave rise to nucleic acids and proteins. Life is this network of mutually binding chemical reactions. Life was bound to rise under the conditions of prebiotic Earth.
Life is a deterministic process that occurs whenever the proper conditions are in place.
DeDuve believes that the same principle that gave rise to the chemistry of life ("protometabolism") must preside over the chemistry of today's life (metabolism).
DeDuve then analyzes how "base pairing" (the "doubling" in the double helix of DNA) is but a special case of a general mechanism of nature, "molecular complementarity". This phenomenon opened the "age of information", in which chemistry that had nothing to do with transmitting information gave rise to replication, hereditarity and evolution, processes which are based on information. RNA emerged before proteins did and were responsible for the survival and reproduction of the early forms of life. RNA molecules were the first catalysts of life. Catalysts sped up the chemical reactions required by life. Because of the fragility of proto-life forms, the process that led to RNA molecules must have been extremely rapid.
Replication was initiated by single-stranded RNA molecules but soon led to double-stranded nucleid acids. The mechanism of pairing naturally enables the process of replication, as originally noted by Crick himself (the double works as a negative and a positive, one being the template for the assembly of the other). RNA molecules made of the four A,G,U and C bases had the advantage that could be replicated, thanks to base pairings. RNA genes were born. Selection began operating. Protein synthesis began occurring.
The next quantum leap was the formation of the genetic code and the assembly of a translation apparatus. Then, the separation of replication and translation gave rise to DNA.
Membranes, outer defenses were born because the protocell had to devise new more efficient ways to derive energy from the environment (transmitting signals from the cell to the environment and viceversa, binding with the environment). Life became a property of discrete, autonomous units.
At the same time, cell division began to support replication.
Each step in the growth of life was providing an incremental selective advantage.
In other words, information-based chemistry allowed for the assembly of a cellular structure, which is the one common ancestor to all forms of life on Earth.
DeDuve believes in one and only one origin of life for the simple reason that life is one: there is only one "life" we are familiar with, the one made of genetic code, metabolism, etc. All "living" creatures share the same "living" processes.
Multi-cellular organisms were created over a long period of time (possibly as long as one billion years). Prokaryotes (bacteria) evolved into eukaryotes: the cell grew more complex, the cell became capable of eating other cells, the cell established endosymbiosis (permanent symbiosis) with other cells.
The next accelerating factor was sexual reproduction, again due to constrained chance, which led to the biodiversity we are familiar with in our age and to the complex interplay of organisms within the same ecosystem. The next major step was the development of brains, and the advent of consciousness, which is now reshaping the course of life on Earth. Both life and mind are deterministic consequences of the matter of this universe, not mere chance events.
A leitmotiv of the evolution of life is "constrained contingency": mutations occur by chance, but are constrained by physical, chemical and environmental factors. DeDuve therefore reconciles chance and necessity.