Self and the Beginning of Life 61“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanitysurvive and propagate, giving rise to individual diversity, adaptation, and
eventually the production of new species. This mechanism, called natu-
ral selection, is the theme of Darwinian evolution. “Selection” is possible
because organisms produce more offspring than natural resources can
support, and the survival of the fittest is a matter of competition.
Darwinian evolution received a boost in the early 20th century,
when genetics was accepted and integrated into the theory. It was then
realized that gene mutation is a major cause of variation across genera-
tions. The mechanism of mutation was explained in the mid-20th cen-
tury by the recognition of DNA as the genetic material and the advent
of the double-helical Watson-Crick model of DNA, which provides a
molecular mechanism for replication and inheritance. The natural ten-
dency to make occasional errors in copying a DNA chain is the reason
why mutation spontaneously occurs. With this insight Darwinian evo-
lution can be reduced from the biological to the molecular level — the
so-called “molecular evolution”. For example, a mutation that changes
one nucleobase in the DNA can alter the protein sequence, making it
more, or less, active as an enzyme, thus affecting the chance of survival
for the organism.
However, I like to point out that molecular evolution makes sense
only in the context of cellular life, for ultimately it is the survival of the
cell that counts. Contrary to this idea, some people equate changes in
the DNA molecule (or any other replicating molecule), under any cir-
cumstances, as molecular evolution in the Darwinian sense. They insist
that, when extrapolated to the pre-biotic era, the speed of replication
and abundance of a hypothetical DNA molecule, even in a cell-free sit-
uation, qualifies for evolution.
For the sake of argument, it will be helpful for me to recount an
experiment performed by Spiegelman and his colleagues in the 1960s,
considered by some to be a prototype of pre-cellular “molecular evo-
lution”.^81 Spiegelman and his colleagues studied the in vitro replica-
tion of an RNA virus called Q-beta. (Normally only DNA is capable of
replication, but in Q-beta, RNA is the genetic material and it functions