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

122 THE POSSIBLE AND THE ACTUAL
space of the Library of Mendel, but it does put a difficult burden of proof on
anyone who thinks that there are laws of biology over and above the laws of
mathematics and physics. Consider the fate of "Dollo's Law," for instance.
'Dollo's Law' states that evolution is irreversible....[But] There is no reason
why general trends in evolution shouldn't be reversed. If there is a trend
towards large antlers for a while in evolution, there can easily be a subsequent
trend towards smaller antlers again. Dollo's Law is really just a statement
about the statistical improbability of following exactly the same
evolutionary trajectory twice (or indeed any particular trajectory), in
either direction. A single mutational step can easily be reversed. But for
larger numbers of mutational steps... the mathematical space of all possible
trajectories is so vast that the chance of two trajectories ever arriving at the
same point becomes vanishingly small __ There is nothing mysterious or
mystical about Dollo's Law, nor is it something that we go out and 'test' in
nature. It follows simply from the elementary laws of probability. [Dawkins
1986a, p. 94.]
There is no shortage of candidates for the role of "irreducible biological
law." For instance, many have argued that there are "developmental laws" or
"laws of form" that constrain the relation between genotype and pheno-type.
In due course we will consider their status, but already we can locate at least
some of the most salient constraints on biological possibility as not "laws of
biology" but just inescapable features of the geometry of design space, like
Dollo's Law (or the Hardy-Weinberg Law of gene frequency, which is
another application of probability theory, pure and simple).
Take the case of the horned birds. As Maynard Smith notes, there aren't
any, and we don't know why. Might it be because they are ruled out by a
biological law? Are horned birds flat impossible? Would they have to be
inviable in any and all possible environments, or is there simply no path at all
"from here to there" because of restrictions on the genome-reading process?
As we have already noted, we should be impressed by the severe restrictions
encountered by this process, but we should not be carried away. Those
restrictions may not be a universal feature, but a temporally and spatially
local feature, analogous to what Seymour Papert has dubbed the QWERTY
phenomenon in the culture of computers and keyboards.
The top row of alphabetic keys of the standard typewriter reads QWERTY.
For me this symbolizes the way in which technology can all too often serve
not as a force for progress but for keeping things stuck. The QWERTY
arrangement has no rational explanation, only a historical one. It was
introduced in response to a problem in the early days of the typewriter:
The keys used to jam. The idea was to minimize the collision problem by
separating those keys that followed one another frequently.... Once
Possibility Naturalized 123
adopted, it resulted in many millions of typewriters and ... the social cost
of change ... mounted with the vested interest created by the fact that so
many fingers now knew how to follow the QWERTY keyboard. QWERTY
has stayed on despite the existence of other, more "rational" systems.
[Papert 1980, p. 33.] 12
The imperious restrictions we encounter inside the Library of Mendel may
look like universal laws of nature from our myopic perspective, but from a
different perspective they may appear to count as merely local conditions,
with historical explanations. 13 If so, then a restricted concept of biological
possibility is the sort we want; the ideal of a universal concept of biological
possibility will be misguided. But as I have already allowed, this does not
rule out biological laws; it merely sets the burden of proof for those who want
to propose any. And in the meantime, it gives us a frame-work for describing
large and important classes of regularity we discover in the patterns in our
biosphere.
CHAPTER 5: Biological possibility is best seen in terms of accessibility (from
some stipulated location) in the Library of Mendel, the logical space of all
genomes. This concept of possibility treats the connectedness of the Tree of
Life as a fundamental feature of biology, while leaving it open that there may
also be biological laws that will also constrain accessibility.
CHAPTER 6: The R and D done by natural selection in the course of creating
actual trajectories in the Vast space of possibilities can be measured to some
extent. Among the important features of this search space are the solutions to
problems that are perennially attractive and hence predictable, like forced
moves in chess. This explains some of our intuitions about originality,
discovery, and invention, and also clarifies the logic of Darwinian inference
about die past. There is a single, unified Design Space in which the processes
of both biological and human creativity make their tracks, using similar
methods.
12. Others have exploited the QWERTY phenomenon to make similar points: David
1985, Gould 1991a.
13. George Williams (1985, p. 20) puts it this way: "1 once insisted that'... the laws of
Physical science plus natural selection can furnish a complete explanation for any biological
phenomenon' [Williams 1966, pp. 6-7]. I wish now I had taken a less extreme
view and merely identified natural selection as the only theory that a biologist needs in
addition to those of the physical scientist. Both the biologist and the physical scientist
need to reckon with historical legacies to explain any real-world phenomenon."