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

Drifting and Lifting Through Design Space 125
CHAPTER SIX
Threads of Actuality in
Design Space
1. DRIFTING AND LIFTING THROUGH DESIGN SPACE
The actual animals that have ever lived on Earth are a tiny subset of the
theoretical animals that could exist. These real animals are the products
of a very small number of evolutionary trajectories dvough genetic
space. The vast majority of theoretical trajectories through animal space
give rise to impossible monsters. Real animals are dotted around here
and there among the hypothetical monsters, each perched in its own
unique place in genetic hyperspace. Each real animal is surrounded by
a little cluster of neighbours, most of whom have never existed, but a
few of whom are its ancestors, its descendants and its cousins.
—RICHARD DAWKINS 1986a, p. 73
The actual genomes that have ever existed are a Vanishingly small subset
of the combinatorially possible genomes, just as the actual books in the
world's libraries are a Vanishingly small subset of the books in the imaginary
Library of Babel. As we survey the Library of Babel, we may be struck by
how hard it is to specify a category of books that isn't Vast in membership,
however Vanishingly small it is in relation to the whole. The set of books
composed entirely of grammatical English sentences is a Vast but Vanishing
subset, and the set of readable, sense-making books is a Vast but Vanishing
subset of it. Vanishingly hidden in that subset is the Vast set of books about
people named Charles, and within that set (though Vanishingly hard to find)
is the Vast set of books purporting to tell the truth about Charles Darwin, and
a Vast but Vanishing subset of these consists of books composed en-
tirely in limericks. So it goes. The number of actual books about Charles
Darwin is a huge number, but not a Vast number, and we won't get down to
that set (that set as of today, or as of the year 3000 A.D. ) by just piling on the
restricting adjectives in this fashion. To get to the actual books, we have to
turn to the historical process that created them, in all its grubby particularity.
The same is true of the actual organisms, or their actual genomes.
We don't need laws of biology to "prevent" most of the physical possibilities
from becoming actualities; sheer absence of opportunity will account
for most of them. The only "reason" all your nonactual aunts and uncles
never came into existence is that your grandparents didn't have time or
energy (to say nothing of the inclination) to create more than a few of the
nearby genomes. Among the many nonactual possibles, some are—or were—
"more possible" than others: that is, their appearance was more probable than
the appearance of others, simply because they were neighbors of actual
genomes, only a few choices away in the random zipping-up process that
puts together the new DNA volume from the parent drafts, or only one or a
few random typos away in the great copying process. Why didn't the nearmisses
happen? No reason; they just didn't happen to happen. And then, as
the actual genomes that did happen to happen began to move away from the
locations in Design Space of the near-misses, their probability of ever
happening grew smaller. They were so close to becoming actual, and then
their moment passed! Will they get another chance? It is possible, but Vastly
improbable, given the Vast size of the space in which they reside.
But what forces, if any, bend the paths of actuality farther and farther away
from their locations? The motion that occurs if there are no forces at all is
called random genetic drift. You might think that drift, being random, would
tend always to cancel itself out, bringing the path back to the same genomes
again and again in the absence of any selective forces, but the very fact that
there is only limited sampling in the huge space (which has a million
dimensions, remember!) leads inevitably to the accumulation of "distance"
between actual genomes (the upshot of "Dollo's Law").
Darwin's central claim is that when the force of natural selection is imposed
on this random meandering, in addition to drifting there is lifting. Any
motion in Design Space can be measured, but the motion of random drift is,
intuitively, merely sideways; it doesn't get us anywhere important. Considered
as R-and-D work, it is idle, leading to the accumulation of mere typographical
change, but not to the accumulation of design. In fact, it is worse
than that, for most mutations—typos—will be neutral, and most of the typos
that aren't neutral will be deleterious. In the absence of natural selection, the
drift is inexorably downward in Design Space. The situation in the Library of
Mendel is thus precisely like the situation in the Library of Babel. Most
typographical changes to Moby Dick can be supposed to be practically