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

192 BIOLOGY IS ENGINEERING Darwin Is Dead—Long Live Darwin! 193
nonical or wild-type text of that work was, but the identity of the work would
hardly be in jeopardy. James Joyce's Ulysses would be a good case in point.)
Eigen points out that this distribution of the "essence" over a variety of
nearly identical vehicles turns out to make that essence much more movable,
much more adaptable, especially in "rugged" fitness landscapes, with
multiple peaks and few smooth slopes. It permits the essence to send out
efficient scouting parties into the neighboring hills and ridges, ignoring
wasteful exploration of the valleys, and thereby vastly (not Vastly, but
enough to make a huge difference) enhancing its capacity to find higher
peaks, better optima, at some distance from its center, where the (virtual)
wild type sits. 1
The reasons it works are summarized by Eigen as follows:
Functionally competent mutants, whose selection values come close to
that of the wild type (though remaining below it), reach far higher population
numbers than those that are functionally ineffective. An asymmetric
spectrum of mutants builds up, in which mutants far removed from the
wild type arise successively from intermediates. The population in such a
chain of mutants is influenced decisively by the structure of the value
landscape. The value landscape consists of connected plains, hills, and
mountain ranges. In the mountain ranges, the mutant spectrum is widely
scattered, and along ridges even distant relatives of the wild type appear
with finite [that is, not infinitesimal] frequency. It is precisely in the mountainous
regions that further selectively superior mutants can be expected.
As soon as one of these turns up on the periphery of a mutation spectrum
the established ensemble collapses. A new ensemble builds up around the
superior mutant, which thus takes over the role of the wild type___ This
causal chain results in a kind of 'mass action', by which the superior mutants
are tested with much higher probability than inferior mutants, even
if the latter are an equal distance away from the wild type. [Eigen 1992,
p. 25.]
So there is a tight interaction between the shape of the fitness landscape
and the population that occupies it, creating a series of feedback loops,
1. The similarity between these themes and the themes I develop in Consciousness
Explained (1991a) about the need to break up the Cartesian Theater, with its Central
Meaner, and distribute its intelligence work around to a variety of peripheral agents, is of
course no accident. It is, however, mainly a case of convergent evolution, so far as I can
determine. I had not read any of Eigen's work at the time I was writing my book, though
it certainly would have inspired me if I had. A useful bridge between Eigen on molecules
and me on consciousness is Schull 1990 on the intelligence of species, and my commentary,
Dennett 1990a.
leading—usually—from one temporarily stable problem-setting to another.
No sooner do you climb a peak than the whole landscape pitches and billows
into a new mountain range and you start climbing all over again. In fact, the
landscape is constantly shifting under your feet (if you are a quasi-species of
viruses ).
Now, this is really not as revolutionary as Eigen claims. Sewall Wright
himself, in his "shirting balance theory," tried to explain how multiple peaks
and shifting landscapes would be traversable not by individual "wild-type"
exemplars, but by various-sized populations of variants, and Ernst Mayr has
stressed for many years that "population thinking" is at the heart of Darwinism,
something overlooked by geneticists at their peril. So Eigen has
really not revolutionized Darwinism but, rather—no small contribution—
created some theoretical innovations that clarify and strengthen underappreciated
and imperfectly formulated ideas that had been around for years.
When Eigen (1992, p. 125) says, "The (quantitative) acceleration of evolution
that this brings about is so great that it appears to the biologist as a surprising
new quality, an apparent ability of selection to 'see ahead', something that
would be viewed by classical Darwinians as the purest heresy!" he is
indulging in a familiar form of overdramatization, ignoring the many
biologists who at least anticipated, and perhaps even fomented, his "revolution."
After all, when traditional Darwinian theorists postulate fitness landscapes
and then randomly sprinkle genotypes on them in order to calculate what
theory says would happen to them, they know that, in nature, genotypes don't
just get thrown randomly into pre-existing parts of the world. Every model of
a time-consuming process has to start at some arbitrary "moment"; the curtain
rises and the model then plots what happens next. If we look at such a model
and see that at the "outset" it shows a bunch of candidates down in the
valleys, we can be pretty sure that the theorist recognizes that they weren't
"always" down there—whatever that would mean! Wherever on the fitness
landscape there are candidates at one time, there were peaks before, or those
candidates wouldn't be there, so these must be relatively new valleys these
candidates are occupying, a new predicament that evolution has placed before
them. Only that assumption could justify locating the candidates in the
valleys in the first place. Eigen's contribution reinforces the appreciation that
we have to add these complications to the models if we want them actually to
do the work that Darwinians have always supposed that their simpler models
could do.
It is certainly no accident that our appreciation of the need for these much
more complicated models coincides in time (almost down to the month, and
certainly to the year) with our capacity to build and explore such models on
existing computers. No sooner do more powerful computers become
available than we discover with their help that more complex