Giglio-Tos and Pierantoni: A General Theory of Symbiosis that Still Works

Abstract

Giglio-Tos’(GT) theory explained basic features of life and its evolution on the premise that communities tend towards more mutualistic interactions, eventually reaching symbioses. Pierantoni’s characterizations of bacterial and fungal symbioses corroborated a main prediction of this theory—the symbiotic origins of eukaryotic organelles-at a time when another—the switch from haplont to diplont gender systems—came into conflict with Mendelian genetics. The correct switch soon became evident—diplont gender systems derived by reuniting both determinants of haplont gender in the same haploid complement—easily correcting components of GT’s theory affected by having assumed a different one. Soon GT’s basic premises were amply justified by reformulations of older theories also in terms of mathematical models, such as showing that radically different equilibria can easily arise between the same host and symbiote or parasite (Kostitzin) or that complex communities, tightly bound by adversary interactions, tend to be more prone than others to collapse due to perturbations (Volterra). The smallish, at times very small, and ephemeral populations of more fragile communities can easily react to changes in conditions by different, largely haphazard selective modifications; each component species then changes mostly through selective replacements and hybridizations among its modified populations.

At variance from haplonts in which a single change in conditions of life is rather likely to directly fix previously rare alleles, in diplont, multicellular, interbreeding organisms a new selective regime will mainly modify common genotypic polymorphisms, eliminate part of them and select new ones. Novel plastic adjustements are thus easily modified also through polymorphisms, usually turning them into coexisting morphs which, later on, often “segregate” into distinct lineages. For various “Darwinisms”, instead, even crossbreeding multicellular organisms would mostly change as a direct effect of rare, fitter variants being fixed by a single change in conditions, altough far too unlikely, slow and “costly” to account for fast change. According to these Darwinisms, the above positions would be wrong for reasons such as that their Malthusian struggles would be “typological”, or their “group selection” would too easily result in symbioses often entailing “inheritance of acquired characters”. The older theories now have a scarce following, being bitterly opposed by contemporary “;Darwinisms”, arriving at much the same conclusions as the older ones in more sophisticated ways, as well as by popular theories that claim being radically alternative to them. Much as it was a century ago, both Darwinisms and anti-Darwinisms now consider natural selection only in its most inefficient modes of operation so that evolution would pose hard theoretical challenges according to the former while natural selection would be nearly powerless according to the latter. The older theories can easily account also for recent empirical knowledge, perhaps through more detailed specifications such as those on the origins of cells and coding by Cordón, de Duve and Ohnishi, namely cellular coding quite likely arose from collective modifications in communities of RNA organisms, commensual or parasitic and then symbiotic of protocols.