Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
A History of Life
The Belgian biologist Christian de Duve assembled a detailed explanation of how life started and developed, an explanation that is consistent with the data available from Geology, Paleontology and Anthropology.
One of the guiding principles in his search for the origins of life is that the same principle that gave rise to the chemistry of life ("proto-metabolism") must preside over the chemistry of today's life (metabolism).
Life started, in his opinion, with the spontaneous formation of organic molecules that 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 that 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.
In sharp contrast with Monod, life turns out to be a deterministic process that is likely to occur whenever the proper conditions are in place.
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, inheritance and evolution, processes which are based on information. RNA emerged before proteins did and was 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, i.e. outer defenses, were born because the protocell had to devise 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.
Information-based chemistry allowed for the assembly of a cellular structure, which is the one common ancestor to all forms of life on Earth.
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.
Each step in the growth of life was providing an incremental selective advantage.
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.
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.
Complexity and Specialization
Darwin himself objected to the idea that there might be a trend towards complexity in nature. Nothing in the laws of evolution implies that life should evolve towards increased complexity. Nevertheless, the facts seem to tell a different story: eukaryotic cells are more complex than prokaryotic ones, animals and plants are more complex than protists, and so on.
The British biologist Ronald Fisher, tried, indirectly, to justify that fact with his fundamental law: the rate of increase in the average fitness of a population equals the genetic variance in fitness. This law is like the second law of Thermodynamics, which implies that entropy can never decrease. Fisher’s law says that the average fitness of a population can never decrease (because variance is never a negative number).
The British biologist John Maynard-Smith and the Hungarian biologist Eors Szathmary argued against Fisher’s theory and instead proposed that the increase in complexity may originate from very few episodic evolutionary transitions whose goal was not to increase complexity. Their “major transitions” share a common aspect. Each transition affected biological units that were capable of independent replication, and each transition turned them into biological units that needed other biological units in order to replicate. For example, independently replicating nucleid acids evolved into chromosomes (assemblies of molecules that must replicate together). Also, sexless life was replaced by species that have male and female members, and that can replicate only if a male and a female “cooperate”. Ants and bees can only replicate in colonies.
Another side of the same coin is the history of specialization. How this happened is not clear but there must have been a point in time when a set of identical organisms “deteriorated” (or, better, differentiated) into functionally specialized organisms. There was a time when only RNA existed; that world decayed into a world of DNA (that carries out the genetic functions) and proteins (that carry out the function of catalysts). The monolithic cells of prokaryotes evolved into the combination of nucleus, cytoplasm and organelles of the eukaryotes. A world of hermaphrodites morphed into a world of sexual organisms. The members of beehives have specific roles. And so forth.
In these major transitions, sets of identical biological units were replaced by sets of specialized units that needed to cooperate in order to survive and replicate.
Maynard-Smith and Szathmary interpret these transitions also on the basis of information theory: they involve a change in the language that encodes information and a change in the medium that expresses that language. In other words, they are about the way in which information is stored and transmitted.
Maynard-Smith defined progress in evolution as an increase in information transmitted from one generation to another.
The key to evolution is heredity: the way information is stored, transmitted and translated. Evolution of life as we know it relies on information transmission. And information transmission depends on replication of structures.
Evolution was somewhat accelerated, and changed in character, by and because of dramatic changes in the nature of biological replicators, or in the way that information is transmitted by biological replicators. New kinds of coding methods made possible new kinds of organisms.
Today, replication is achieved via genes that utilize the genetic code. But this is only the latest episode in a story that started with the most rudimentary replicators. RNA is capable of playing both the roles of replicator and enzyme, as discovered by the US biophysicist Carl Woese. Thus Maynard-Smith thinks likely that the first replicators were made of RNA.
Szathmary showed that this would also explain why the genetic alphabet consists of four letters: four bases are optimal for ribo-organisms. The genetic alphabet evolved when enzymes were ribozymes and organisms with protein enzymes have simply inherited it. At first RNA molecules performed both the job of information management and of constructing the structures specified in that information.
The first major breakthrough in evolution, the first major change in the technique of replication, was the appearance of chromosomes: when one gene is replicated, all are.
A second major change came with the transition from the solitary work of RNA to the dual cooperation of DNA and proteins: it meant the shift from a unitary source of replication to a division of labor: on one hand the nucleic acids that store and transmit information (i.e., the birth of the genetic code as it is today), and on the other hand the proteins that construct the body. Metabolism was born out of that division of labor and was facilitated by the chemical phenomenon of autocatalysis. Autocatalysis allows for self-maintenance, growth and reproduction. Growth is autocatalysis.
Early on, monocellular organisms (prokaryotes) evolved into multicellular organisms (eukaryotes). The new mechanism that arose was gene regulation: the ability to switch on different genes in different cells depending on the stimuli that the cell receives. The code didn't simply provide the instructions to build the organism, but also how cells contributed to the organism.
Asexual cloning was eventually made obsolete by sex, and sex again changed the rules of the game by shuffling the genetic information before transmitting it. The living world split into animals, plants and fungi that have different information-transmission techniques.
Individuals formed colonies, that developed other means of transmitting information, namely "culture”; and finally social behavior led to language, and language is a form of information transmission itself.
Each of these steps "invented" a new way of coding, storing and transmitting information.
Maynard Smith does not continue the story to what is truly unique about humans: morality. Over the centuries humans have progressively abandoned or at least decried old habits such as war, torture, slavery, racism, gender discrimination, pollution.
Maynard-Smith also introduced Game Theory into Biology. The premise of game theory is that individuals are rational and self-interested Maynard Smith applied this definition to populations (instead of individuals) and interpreted the two attributes biologically: rationality means that population dynamics tend towards stability, and self-interest means fitness relative to the environment.
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