The simplest molecules grouping the four most common elements of the universe H,C,O and N (with the exception of the biologically inert He) are isocyanate HNCO and formamide H2NCOH. Reasons for the availability of formamide on prebiotic Earth are presented. We review evidence showing that formamide in the presence of largely available catalysts and by moderate heating yields the complete set of nucleic bases necessary for the formation of nucleic acids. Formamide also favours the formation of acyclonucleosides and the phosphorylation and trans-phosphorylation of nucleosides, thus providing a plausible chemical frame for the passage from a simple one-carbon compound to nucleic polymers. Physico-chemical conditions exist in which formamide favours the stability of the phosphoester bonds in nucleic polymers relative to that of the same bonds in monomers. Starting from a formamide-laden environment subject only to the laws of chemistry, a hypothesis is outlined sketching the passage towards an aqueous world in which Darwinian rules apply.
Life is a sturdy phenomenon and its initial steps bona fide originated from robust chemical frames based on firm thermodynamic ground. These assumptions on the simplicity and the necessity of the pre-biogenic processes are mitigated by the consideration that the genetic mechanisms onto which relies life-as-we-know-it today are combinatorially elaborated. In passing from the initial self-organization of chemical information to the potentially infinite complexity of interplaying genotypes and phenotypes that we experience today, evolution did necessarily play the key role.
We have focused on two aspects of the problem: the definition of a plausible chemical frame into which the first spontaneous syntheses could have taken place; the evolutionarily relevant selective properties and constrains that the first informational polymers had to deal with. The two aspects are intimately connected.
Is formamide a plausible prebiotic precursor?
The nature of the chemicals that played the role of prebiotic precursors on primitive Earth is still a debated argument. In a general approach to the problem, the following physical and chemical properties of the simple organic compounds under consideration should be taken into account. Namely: (i) the relative abundance of the starting biogenic materials, to be considered a pre-requisite for the early onset [1–4] of genetic processes on this planet; (ii) their stability; (iii) their ability to react to give more complex structures following reproducible pathways. The formation of precursors based on simple chemical processes, and the quasi-simultaneous presence of all the building blocks to be used for the assembling of informational molecules, are other important requisites.