Chemical evolution feedback loops

The origin of life probably occurred in three phases (fig. 1.23) (1) The earliest phase was a period of chemical evolution during which the compounds needed for the nu-cleation of life must have been formed. These compounds include the most important class of biological macromolecules, the nucleic acids. In this phase of evolution, the synthesis of nucleic acids was noninstructed. (2) As soon as some nucleic acids were present, physical forces between them must have led to an instructed synthesis, in which the already formed molecules served as templates for the synthesis of new polymers. It seems likely that feedback loops selected out certain nucleic acids for preferential synthesis. At some point during this period of instructed synthesis more nucleic acids and possibly protein macromolecules were formed. The products of this phase of mo-... 

Generally speaking, the chance to establish autocata-lytic cycles during chemical evolution (Orgel 2003) with or without external selecting influences is rather small. On the other hand, some (not all of the) similarities between product patterns of prebiotic simulation experiments and contemporary biochemistry suggest that the principal biochemical structures kept constant throughout the existence of life on Earth. Hence auto-catalytic feedback loops came into existence only later. 

One definition is that emotions are a chain of events, made np of feedback loops that are meant to restore an individual to a state of equilibrium (Plutchik, 2001). They are very complex because they are usually chemically mediated and influence many metabolic pathways. They are evolution-arily important because they are responsible for heightened awareness of threats, selection of mates, defense of territory, and maintenance of social order (Fignre 6.22.1). 

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