Darwin's Dangerous Idea - Evolution and the Meaning of Life

156 PRIMING DARWIN'S PUMP Molecular Evolution 157
plexity, that of the biological macromolecules, an almost unlimited variety
of structures is possible.
—BERND-OIAF KUPPERS 1990, p. 11
Our task is to find an algorithm, a natural law that leads to the origin of
information.
—MANFRED EIGEN 1992, p. 12
In describing the power of the central claim of Darwinism in the previous
section, I helped myself to a slight (!) exaggeration: I said that every living
thing is the descendant of a living thing. This cannot be true, for it implies an
infinity of living things, a set with no first member. Since we know that the
total number of living things (on Earth, up till now) is large but finite, we
seem to be obliged, logically, to identify a first member—Adam the
Protobacterium, if you like. But how could such a first member come to
exist? A whole bacterium is much, much too complicated just to happen into
existence by cosmic accident. The DNA of a bacterium such as E coli has
around four million nucleotides in it, almost all of them precisely in order. It
is quite clear, moreover, that a bacterium could not get by with much less. So
here is a quandary: since living tilings have existed for only a finite time,
there must have been a first one, but since all living things are complex, there
couldn't have been a first one!
There could only be one solution, and we know it well in outline: before
there were bacteria, with autonomous metabolisms, there were much simpler,
quasi-living things, like viruses, but unlike them in not (yet) having any
living things to live off parasitically. From the chemist's point of view,
viruses are "just" huge, complex crystals, but thanks to their complexity, they
don't just sit there; they "do things." In particular, they reproduce or selfreplicate,
with variations. A virus travels light, packing no metabolic
machinery, so it either stumbles upon the energy and materials required for
self-replication or self-repair, or eventually it succumbs to the Second Law of
Thermodynamics and falls apart. Nowadays, living cells provide concentrated
storehouses for viruses, and viruses have evolved to exploit them, but
in the early days, they had to scrounge for less efficient ways of making more
copies of themselves. Viruses today don't all use double-stranded DNA;
some use an ancestral language, composed of single-stranded RNA (which of
course still plays a role in our own reproductive system, as an intermediary
"messenger" system during "expression"). If we follow standard practice and
reserve the term virus for a parasitic macromolecule, we need a name for
these earliest ancestors. Computer programmers call a cobbled-together
fragment of coded instructions that performs a particular task a "macro," so I
propose to call these pioneers macros, to stress that although they are "just"
huge macromolecules, they are also bits of program or
algorithm, bare, minimal self-reproducing mechanisms—remarkably like the
computer viruses that have recently emerged to fascinate and plague us (Ray
1992, Dawkins 1993) 1 Since these pioneer macros reproduced, they met the
necessary Darwinian conditions for evolution, and it is now clear that they
spent the better part of a billion years evolving on Earth before there were
any living things.
Even the simplest replicating macro is far from simple, however, a composition
with thousands or millions of parts, depending on how we count the
raw materials that go to make it. The alphabet letters Adenine, Cytosine,
Guanine, Thymine, and Uracil are bases that are not too complex to arise in
the normal course of prebiotic affairs. (RNA, which came before DNA, has
Uracil, whereas DNA has Thymine.) Expert opinion differs, however, on
whether these blocks could synthesize themselves by a series of coincidences
into something as fancy as a self-replicator. The chemist Graham Cairns-
Smith (1982, 1985) presents an updated version of Paley's argument, aimed
at the molecular level: The process of synthesizing DNA fragments, even by
the advanced methods of modern organic chemists, is highly elaborate; this
shows that their chance creation is as improbable as Paley's watch in a
windstorm. "Nucleotides are too expensive" (Cairns-Smith 1985, pp. 45-49).
DNA exhibits too much design work to be a mere product of chance, Cairns-
Smith argues, but he then proceeds to deduce an ingenious—if speculative
and controversial—account of how that work might have been done. Whether
or not Cairns-Smith's theory is eventually confirmed, it is well worth sharing
simply because it so perfectly instantiates the fundamental Darwinian
strategy. 2
A good Darwinian, faced yet again with the problem of finding a needle in
a haystack of Design Space, would cast about for a still simpler form of
1. Warning: biologists already use the term macroevolution, in contrast to microevolution,
to refer to large-scale evolutionary phenomena—the patterns of speciation and
extinction, for instance, in contrast to the refinement of wings or changes in resistance to
toxins within a species. What I am calling the evolution of macros has nothing much to
do with macroevolution in that established sense. The term macro is so apt for my
purposes, however, that I have decided to stick with it, and try to offset its shortcomings
with this patch—a tactic Mother Nature also often uses.
2. For just this reason, Richard Dawkins also presents a discussion and elaboration of
Cairns-Smith's ideas in TheBlind Watchmaker (1986a, pp. 148-58). Since Cairns-Smith's
1985 account and Dawkins' elaboration are such good reading for nonexperts, I will refer
you to them for the delicious details, and provide just enough summary here to whet
your appetite, adding the warning that there are problems with Cairns-Smith's hypotheses,
and balancing the warning with the reassurance that even if his hypotheses are all
ultimately rejected—an open question—there are other, less readily understandable,
alternatives to take seriously next.