44 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”would they do? First and foremost, they should also be able to replicate
themselves. But since no self-replicating ribozyme has ever been found
among present-day RNA, the attempt to simulate its existence in the
ancient world can only be carried out in the laboratory.
In 1993, Bartel and Szostak generated a great deal of excitement
by demonstrating that, from a mixture of RNA with random sequences,
a species of RNA can be selected in test tube to perform template-
directed polymerization.^41 Although such notable progress represents
proof of principle, the artificially “evolved” RNA enzyme was obtained
under conditions that could not have been provided by nature on the
early Earth. Some of the problems are listed below: (1) The reactions
were carried out in a well-protected, confined environment (test tubes
or other reaction containers) with pure ingredients, whereas in the
real world all reactions were exposed to a chaotic chemical mix, sub-
jected to unlimited dilutions and multiple side reactions. (2) The reac-
tions were carried out in a highly specific sequence with highly precise
timing, requiring repeated purifications, isolations, and amplifications.
(3) A “relay running” procedure was followed in which no starting
reagent sees its way through the end product. By this I mean that once a
desired product (however small the amount) is identified in each inter-
mediate step, the experimenters purchased (from a chemical company)
a large supply of that product in pure form and used it for the next
reaction step. (4) Some enzyme reagents used were obtained from pre-
existing life forms, such as transcriptase, reverse transcriptase, and DNA
polymerase. (5) Some steps required sophisticated equipment available
only in modern technology, such as the apparatus for polymerase chain
reaction (PCR) and affinity columns utilizing biotin-streptavidin pairing.
In short, the “selection” process was planned by highly intelligent exper-
imenters and carried out in a modern laboratory setup, not by nature
in a primeval environment. Yet, in spite of this degree of sophistication,
the replicative function of the artificially generated ribozyme was slow
and error-prone, and the copied segment was of limited length. Thus,