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

198 BIOLOGY IS ENGINEERING Function and Specification 199
made the fundamental assumption that the wings were functional, and that
their function was flight (which might not be as obvious to them as we, who
have seen them do it, think), they could use this assumption to "read off' the
implicit information about an environment for which these wings would be
well designed. Suppose they then asked themselves how all this aerodynamic
theory came to be implicit in the structure, or, in other words: How did all
this information get into these wings? The answer must be: By an interaction
between the environment and the seagull's ancestors. ( Dawkins 1983a
explores these issues in more detail.)
The same principle applies at the most basic level, where the function is
specification itself, the function on which all other functions depend. When
we wonder, with Monod, how the three-dimensional shape of the proteins
gets fixed, given that the information in the genome must underspecify them,
we see that only a pruning of the nonfunctional (or less functional) could
explain it. So the acquisition of a particular shape by a molecule involves a
mixture of historical accident on the one hand and the "discovery" of
important truths on the other.
From the outset, the process of the design of molecular "machines" exhibits
these two features of human engineering. Eigen (1992, p. 34) provides
a good instance of this in his reflections on the structure of the DNA code.
"One might well ask why Nature has used four symbols, when she might just
as well have made do with two." Why indeed? Notice how naturally and
inevitably a "why" question arises at this point, and notice that it calls for an
"engineering" answer. Either the answer is that there is no reason—it is
historical accident, pure and simple—or there is a reason: a condition was or
is present that makes this the right way or best way for the coding system to
get designed, given the conditions that obtained. 4
All the deepest features of molecular design may be considered from the
engineering perspective. On the one hand, consider the fact that macromolecules
come in two basic shape categories: symmetrical and chiral (with
left-handed and right-handed versions). There is a reason why so many
should be symmetrical:
The selective advantage in a symmetrical complex is enjoyed by all the
subunits, while in an asymmetric complex the advantage is only effective
in the subunit in which the mutation arises. It is for this reason that we find
so many symmetric structures in biology, "because they were able to make
the most effective use of their advantage, and thus—a posteriori—won the
4. Eigen suggests that there is a reason why there are four letters, not two, but I am not
going to pass it on. Perhaps you can figure out for yourself what it might be before seeing
what Eigen says. You already have at your fingertips the relevant principles of engineering
to give it a good shot.
selection competition; this was not, however, because symmetry is—a priori—an
indispensable requirement for the fulfillment of a functional purpose." [Küppers
1990, p. 119, incorporating a quotation from Eigen and Winkler-Oswatitsch
1975.]
But what about the asymmetric or chiral shapes? Is there a reason why
they should be one way—left-handed, say—rather than the other? No, probably
not, but: "Even if there is no a priori physical explanation for the
decision, even if it was just a brief fluctuation that gave one or the other
equivalent possibility a momentary advantage, the self-reinforcing character
of selection would turn the random decision into a major and permanent
breach of symmetry. The cause would be a purely 'historical' one" (Eigen
1992, p. 35 ). 5
The shared chirality of organic molecules (in our part of the universe ) was
thus probably another pure QWERTY phenomenon, or what Crick (1968) has
called a "frozen accident." But even in the case of such a QWERTY
phenomenon, if the conditions are just right and the opportunities and hence
pressures are great enough, the tables might be turned and a new standard
established. This is apparently just what happened when the DNA language
displaced the RNA language as the lingua franca of encoding for complex
organisms. The reasons for its preferability are clear: by being doublestranded,
the DNA language permitted a system of error-correcting or
proofreading enzymes, which could repair copying errors in one strand by
reference to its mate. This made the creation of longer, more complicated
genomes feasible (Eigen 1992, p. 36).
Note that this reasoning does not yield the conclusion that double-stranded
DNA must develop, for Mother Nature had no advance intention to create
multicellular life. It just reveals that // double-stranded DNA happens to
begin to develop, it opens up opportunities that are dependent on it. Hence it
becomes a necessity for those exemplars in the space of all possible life
forms that avail themselves of it, and if those life forms prevail
5. Danny Hillis, the creator of the Connection Machine, once told me a story about some
computer scientists who designed an electronic component for a military application (I
think it was part of a guidance system in airplanes). Their prototype had two circuit
boards, and the top one kept sagging, so, casting about for a quick fix, they spotted a brass
doorknob in the lab which had just the right thickness. They took it off its door and
jammed it into place between the two circuit boards on the prototype. Sometime later,
one of these engineers was called in to look at a problem the military was having with the
actual manufactured systems, and found to his amazement that between the circuit
boards in each unit was a very precisely milled brass duplicate of the original doorknob.
This is an Ur-story that has many well-known variations in engineering circles and among
evolutionary biologists. For instance, see Primo Levi's amusing account of the mystery of
the varnish additive in The Periodic Table ( 1984).