Category: Complexity

In 1964 Quastler's book The Emergence of Biological Organization was published posthumously. In 2002, Harold J. Morowitz described it as a "remarkably prescient book" which is "surprisingly contemporary in outlook". In it Quastler pioneers a theory of emergence, developing model of "a series of emergences from probionts to prokaryotes".

The work is based on lectures given by Quastler during the spring term of 1963, when he was Visiting Professor of Theoretical Biology at Yale University. In these lectures Quastler argued that the formation of single-stranded polynucleotides was well within the limits of probability of what could have occurred during the pre-biologic period of the Earth. However, he noted that polymerization of a single-stranded polymer from mononucleotides is slow, and its hydrolysis is fast; therefore in a closed system consisting only of mononucleotides and their single-stranded polymers, only a small fraction of the available molecules will be polymerized. However, a single-stranded polymer may form a double-stranded one by complementary polymerization, using a single-stranded polynucleotide as a template. Such a process is relatively fast and the resulting double-stranded polynucleotide is much more stable than the single single-stranded one since each monomer is bound not only along the sugar phosphate backbone, but also through inter-strand bonding between the bases.

The capability for self-replication, a fundamental feature of life, emerged when double-stranded polynucleotides disassociated into single-stranded ones and each of these served as a template for synthesis of a complementary strand, producing two double-stranded copies. Such a system is mutable since random changes of individual bases may occur and be propagated. Individual replicators with different nucleotide sequences may also compete with each other for nucleotide precursors. Mutations that influence the folding state of polynucleotides may affect the ratio of association of strands to dissociation and thus the ability to replicate. The folding state would also affect the stability of the molecule. These ideas were then developed to speculate on the emergence of genetic information, protein synthesis and other general features of life.

Lily E. Kay says that Quastler's works "are an illuminating example of a well reasoned epistemic quest and a curious disciplinary failure". Quastler's aspiration to create an information based biology was innovative, but his work was "plagued by problems: outdated data, unwarranted assumptions, some dubious numerology, and, most importantly, an inability to generate an experimental agenda." However Quastler's "discursive framework" survived.

Forty-five years after Quastler's 1964 proposal, Lincoln and Joyce described a cross-catalytic system that involves two RNA enzymes (ribosymes) that catalyze each other's synthesis from a total of four component substrates. This synthesis occurred in the absence of protein and could provide the basis for an artificial genetic system.