On the Evolution of Biochemical Syntheses

Abstract

A hypothesis is presented which might explain the evolution of stepwise reactions when the intermediate products confer no direct selective ad vantage on the individual: to wit, that the last step in the chain was the first to be acquired, the penultimate next, etc. It is suggested that the first living entity was a completely heterotropic unit, reproducing itself at the expense of prefabricated organic molecules in its environment. With the depletion of the specific substrates in the environment, further multiplication was limited until mutation made possible the utilization of other available substances. With this event the evolution of biosynthesis began. With the destruction of the organic environment, the conditions necessary for operation of the mechanism ceased to exist, and further evolution would rely on the chance combination of genes resulting in the development of short reaction chains utilizing substrates whose synthesis had previously been acquired.