The origins of life and the mechanisms of biological evolution Francisco Carrapiço * Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Vegetal, Centro de Biologia Ambiental, Bloco C2, Campo Grande, 1749-016 Lisboa, Portugal ABSTRACT Evolution is usually taught as the result of mutations and genetic recombinations combined with natural selection, but most living forms have symbiotic relationships with microorganisms, and in this sense symbiogenesis seems to play a very important role in the origin and life evolution. Symbiosis is an important support for the acquisition of new genomes and new metabolic capacities, which drives living forms’ evolution. In this sense, the evolutionary changes can be explained by an integrated cooperation between organisms, in which symbiosis acts, not as an exception, but rather as the rule in nature. Beginning with the eukaryotic cell formation, symbiogenesis appears to be the main evolutionary mechanism in the establishment and maintenance of biomes, as well as the foundation of biodiversity, based on rather suddenly evolutionary novelty, which challenges the Darwinian gradualism. These principles can be applied to the life on Earth and beyond. Keywords: biological evolution, origins of life, symbiosis, symbiome 1. INTRODUCTION In a recent work 1 Gilbert V. Levin has theorized, in a brillant way, the application of Darwinian principles to the evolution of life on Mars, suggesting that the “Mars life evolved from microorganisms identical, or similar to, the early forms that have been identified on Earth” and “Martian and Earth life forms are of common ancestry, therefore genetically similar, and sharing common metabolism and chirality”. We believe that these principles can be extended, incorporating symbiogenic mechanisms in biological evolution. For many scientists, symbiosis is still considered as an exception among biological phenomena and not as a common rule in nature. This issue reflects itself in an interpretative reality of the biological evolution where symbiosis remains mainly peripherical to contemporary evolutionary theory 2 , and often considered as a special type of host-parasite relationship. The approach of the traditional evolutionist authors, in relation to this phenomenon, consists in a point of view that emphatizes symbiosis as a residual aspect of the evolution problem. Recent data 3,4,5 , however, point to the exact opposite direction, demonstrating that symbiosis is a factor of evolutive change, giving rise rather suddenly to evolutionary novelty which, in our point of view, challenges several Darwinian and neo-Darwinian tenets, namely gradualism. This situation has important consequences, not only in the way we perceive evolution, but also in the conceptual organization and tenets of Modern Synthesis. 2. SYMBIOGENESIS AND THE ORIGIN AND EVOLUTION OF LIFE After the first studies on lichens in the XIX century, namely the knowledge of its biological structure and the symbiotic relationships established between the alga and the fungi, symbiosis appears as a new mode of organization of living * e-mail: f.carrapico@fc.ul.pt; phone: +351 217500381; fax: + 351 217500048; web: azolla.fc.ul.pt Invited Paper Instruments, Methods, and Missions for Astrobiology IX, edited by Richard B. Hoover, Gilbert V. Levin, Alexei Yu. Rozanov, Alexander Spirin, Proc. of SPIE Vol. 6309, 63090O, (2006) · 0277-786X/06/$15 · doi: 10.1117/12.681946 Proc. of SPIE Vol. 6309 63090O-1