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

314 CONTROVERSIES CONTAINED A Clutch of Harmless Heresies 315
Darwinism even if they were confirmed. Probably the best known has been
championed in recent years by the maverick astronomer Fred Hoyle, who
argues that life did not originate—could not have originated—on Earth, but has
to have been "seeded" from outer space (Hoyle 1964, Hoyle and Wickramasinghe
1981). Francis Crick and Leslie Orgel (1973, and Crick 1981)
point out that this idea of panspermia has been championed in various forms
since early in the century, when Arrhenius ( 1908) coined the term, and,
however unlikely it may seem, it is not an incoherent idea. It is not (yet)
disprovable that primitive life forms (something as "simple" as a macro or as
complex as a bacterium) arrived by asteroid or comet from some other region
of the universe and colonized our planet. Crick and Orgel go a step further: it is
even possible that the panspermia was directed, that life began on Earth as a
result of our planet's being deliberately "infected" or colonized by life forms
from somewhere else in the universe that got a head start on us, and indeed
indirectly produced us. If we can now send a spacecraft loaded with life forms
to another planet—and we can, but should not—then, by parity of reasoning,
others could have done it. Since Hoyle—unlike Crick and Orgel—has voiced
the suspicion (1964, p. 43) that, unless panspermia is true, "life has little
meaning, but must be judged a mere cosmic fluke," it is not surprising that
many, including Hoyle himself, have supposed that panspermia, if confirmed,
would shatter Darwinism, that dreaded threat to the meaning of life. And since
panspermia is often treated with derision by biologists—"Hoyle's Howler"—
the illusion is fostered that here is a grave threat indeed, one that strikes at the
very core of Darwinism. Nothing could be further from the truth. Darwin
himself surmised that life began on Earth in some warm little pond, but it
might equally have started in some hot, sulfurous underground pressure-cooker
(as has recently been proposed by Stetter et al. 1993), or, for that matter, on
some other planet, whence it traveled here after some astronomical collision
pulverized its birthplace. Wherever and whenever life started, it had to
bootstrap itself by some version of the process we explored in chapter 7—that
is what orthodox Darwinism insists upon. And as Manfred Eigen has pointed
out, panspermia would do nothing to solve the difficult problem of how this
bootstrapping happened: "The discrepancy between the numbers of sequences
testable in practice and imaginable in theory is so great that attempts at
explanation by shifting the location of the origin of life from Earth to outer
space do not offer an acceptable solution to the dilemma. The mass of the
universe is 'only' 10 29 times, and its volume 'only' 10 57 times, that of the Earth"
(Eigen 1992, p. 11).
The reason orthodoxy prefers to assume a birthplace on Earth is that this is
the simplest and most scientifically accessible hypothesis. That does not
make it true. Whatever happened, happened. If Hoyle is right, then (darn it)
we will find it much harder to confirm or disconfirm any detailed hypoth-
eses about exactly how life started. The hypothesis that life began on Earth has
the virtue of putting some admirably tough constraints on storytelling: the whole
story has to unfold in under five billion years, and it has to start with conditions
known to have existed on Earth in the early days. Biologists like having to work
within these constraints; they want deadlines and a short list of raw materials, the
more demanding the better. 1 So they hope that no hypothesis will ever be
confirmed that opens up vast possibilities that will be well-nigh impossible for
them to evaluate in detail. The arguments that Hoyle and others have given for
panspermia all belong in the phylum of "otherwise there's not enough time," and
evolutionary theorists much prefer to keep the geological deadlines intact and
hunt for more cranes to do all the lifting in the time available. So far, this policy
has borne excellent results. If Hoyle's hypothesis were someday confirmed, it
would be a gloomy day for evolutionary theorists, not because it would overthrow
Darwinism, but because it would make important features of Darwinism less
disconfirmable, more speculative.
For the same reason, biologists would be hostile to any hypothesis that
proposed that ancient DNA had been tampered with by gene-splicers from
another planet who became high-tech before we did, and played a trick on us.
Biologists would be hostile to the hypothesis, but would have a hard time
disproving it. This raises such an important point about the nature of evidence
in evolutionary theory that it is worth exploring in greater detail, with the
help of a few thought experiments (drawn from Dennett 1987b, 1990b).
As many commentators have noted, evolutionary explanations are inescapably
historical narratives. Ernst Mayr (1983, p. 325) puts it this way.
"When one attempts to explain the features of something that is the product of
evolution, one must attempt to reconstruct the evolutionary history of this
feature." But particular historical facts play an elusive role in such explanations.
The theory of natural selection shows how every feature of the
natural world can be the product of a blind, unforesightful, nonteleolog-ical,
ultimately mechanical process of differential reproduction over long periods of
time. But of course some features of the natural world—the short legs of
dachshunds and Black Angus beef cattle, the thick skins of tomatoes—are the
products of artificial selection, in which the goal of the
1. For just this reason, biologists have mixed emotions about the recent (apparent)
discovery by J. William Schopf (1993) of fossil microbes roughly a billion years older
(3.5 billion instead of 2.5 billion) than orthodoxy has recently supposed. If confirmed,
this would drastically revise a lot of standard assumptions about the intermediate deadlines,
giving more time for the evolution of advanced forms ("Whew!"), but only by
reducing the time available for the process of molecular evolution to get all the way to
microbes ("Uh oh!").