**1. Introduction**

534 The Complex World of Polysaccharides

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1542.

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The Red Queen Effect is an evolutionary hypothesis [1]. This evolutionary concept is named for the Red Queen´s comment to Alice in Through the Looking Glass that "it takes all the running you can do, to stay in the same place". It posits that multicellular organisms with long life cycles must constantly change, adaptation process driven by the changing conditions of the environment, in order to survive the onslaught of potentially lethal pathogens which have much shorter life cycles and can thus evolve orders of magnitude faster.

Viruses play a relevant role in these new evolutionary mechanisms by transferring of genes to and from the hosts they parasite [2]. Over the past three decades, it has become apparent that viruses are ubiquitous, abundant and ecologically important in the environment [3]. As phylogenetic analysis shows, nearly all organisms of all kingdoms have become infected by viruses since the beginning of life. The great impact that viruses can have on the genetic systems is well illustrated by the evolution of mitochondria. In reference [4] have shown, the existence of a strong selection pressure has pushed for the replacement of cellular enzymes by viral ones in mitochondria and chloroplasts. In both organelles, this replacement has been associated with profound modifications in the mechanism of DNA replication and chromosome structure [5]. The fact that viruses are probably very ancient allows better understanding their extraordinary diversity, explaining why most viral proteins inferred from genome sequencing have no cellular homologues [6]. Besides, the existence in the biosphere of an unlimited reservoir of viral proteins has provided opportunities at different steps of the evolutionary process, to introduce new functions into organisms.

© 2012 Carlucci et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

At the present, it remains controversial the inclusion of viruses in the "tree of life". Several authors assume viruses are non-living organisms and believe their properties are driven solely by thermodynamically spontaneous reactions while others give priority to the fact that phylogenetic tree is based on the genomic content of its components, not the physical manifestations of these genomes. Moreover, the fact that viral genomes carried inside virions encode gene products that allow for adaptation and response to changing intracellular and extracellular conditions favors the inclusion of these agents in the tree of life [7,8].

The oligosaccharides chains (glycans) attached to cell surface and extracellular proteins and lipids are known to mediate many important biological roles [9,10]. However, for many glycans, there are still no evident functions that are of obvious benefit to the organism that synthesizes them. In 1949, Haldane postulated "Now every species of mammal and bird so far investigated has shown quite surprising biochemical diversity by serological tests. The antigens concerned seem to be proteins to which polysaccharides are attached. We do not know their functions in the organism, though some of them seem to be part of the structure of the cell membrane. I wish to suggest that they may play a part in disease resistance, a particular race of bacteria or virus being adapted to individuals of a certain range of biochemical constitutions, while those of other constitutions are relatively resistant" [11]. In [12], suggested that glycan diversification in complex multicellular organisms is driven by evolutionary selection pressures of both endogenous and exogenous origin. They also argued that exogenous selection pressures mediated by viral and microbial pathogens and parasites that recognize glycans have played a more prominent role, favoring intra-and interspecies diversity.
