John Maynard Smith & Eors Szathmary:
THE MAJOR TRANSITIONS IN EVOLUTION (W. H. Freeman, 1995)


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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.

The British biologist John Maynard-Smith and the Hungarian biologist Eors Szathmary believe that evolution was somewhat accelerated, and changed in character, by and because of dramatic changes in the nature of biological replicators, or in the way information is transmitted by biological replicators. New kinds of coding methods made possible new kinds of organisms.

They propose 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. In other words, each "major transition" seems to produce (or be produced by) cooperation. For example, independently replicating nucleid acids evolved into chromosomes (assemblies of molecules that must replicate together). For example, 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.

This also opens a window on the history of socialization, or cooperative behavior. Far from being a recent invention, socialization arose when specialization arose. Originally, one can envision a world of multifunctional self-sufficient biological entities. When these evolved into specialized entities, the need for them to socialize was born. Division of labor among a group of specialists is more effective than a multifunctional non-specialist but only if the specialists cooperate. And thus the multifunctional cell led to cellular organization and eventually to bodies with specialized limbs and organs that eventually led to societies of specialists (ants, bees, humans). Altruism, or at least division of labor and cooperation, appeared very early in the history of life, as soon as molecules were enclosed within membranes.

After all, cooperation was inherent in Mendel's laws: a gene's chances of surviving in future generations depends on the success of the cell that hosts that gene, a success that depends on the success of all the other genes that determine the life of that cell. Hence a gene has a vested interest in "cooperating" with the other genes. The cell would not survive if its genes did not form an efficient society.

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 step in a story that started with the earliest, 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. This would also explain why the genetic alphabet consists of four letters: four bases are optimal for ribo-organisms. The genetic alphabet evolved when 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 informations.

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, 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.


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