(Copyright © 2000 Piero Scaruffi | Legal restrictions - Termini d'uso )
This book is a popular introduction to the ideas embraced in
THE MAJOR TRANSITIONS IN EVOLUTION.
Over the millennia life has become more complex but nothing in the law of evolution says that future generations will be more complex (it merely says that future generations will be "better adapted"). To understand "the origin of complexity" (which would be a better title for this book) one has to look at how adaptation is improved from one generation to the next one. What is transmitted is not a specific structure but the instructions for constructing that structure (the genetic information). John Maynard Smith and Eors Szathmary believe that the mechanism for storing and transmitting information have changed. These mechanisms have caused life to become more complex.
Life is defined by two complementary process: metabolism (growth) and evolution. Neither is unique to living beings but the combination of the two is. Growth is largely the byproduct of the chemical process of autocatalysis, which also accounts for self-maintenance and reproduction. In other words, a metabolic system must be (chemically speaking) autocatalytic. The process of evolution has a more convoluted origin.
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, the first genes. 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. At first RNA molecules performed both the job of information management and of constructing the structures specified in that informations. 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"), 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 code didn't simply specify 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. Protists split into animals, plants, fungi, that have different information-transmission techniques. Individuals formed colonies, that developed other means of transmitting information, namely "culture╬Ú╬Ý; 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.
For each of these steps the authors provide detailed but speculative explanations, a sort of "whodunit" of biology.