The Nature of Science 11Another issue in the philosophy of science has come up as a result of the creationism con-
troversy. Berkeley lawyer (not a scientist or a theologian or a philosopher of science) Phillip
Johnson criticizes science because it makes the “naturalistic assumption.” In other words, sci-
ence assumes only natural, not supernatural, processes in the attempt to understand nature.
To Johnson, this is unfair; if science excludes the supernatural even before the debate can
begin, then it excludes the possibility of any conclusion but evolution. In his book Darwin
on Trial, Johnson writes, “Naturalism assumes the entire realm of nature to be a closed sys-
tem of material causes and effects, which cannot be influenced by anything from ‘outside.’
Naturalism does not explicitly deny the mere existence of God, but it does deny that a super-
natural being could in any way influence natural events, such as evolution, or communicate
with natural creatures like ourselves” (Johnson 1991:114–115). Johnson’s attack concludes by
arguing that if supernatural causes were allowed, other conclusions besides evolution (such
as creationism) might be reached.
This argument is so confused and disingenuous that it almost doesn’t require rebuttal.
As Pennock (1999:190) points out, Johnson has conflated two entirely different naturalistic
concepts. Ontological or metaphysical naturalism (the kind mentioned in the Johnson quotes
above) makes the bold claim that the natural is all that exists and that there is no super-
natural. That is an interesting philosophical issue, but that does not reflect what scientists
are doing. Instead, scientists practice methodological naturalism, where they use naturalistic
assumptions to understand the world but make no philosophical commitment as to whether
the supernatural exists or not. Scientists don’t exclude God from their hypotheses because
they are inherently atheistic or unwilling to consider the existence of God; they simply can-
not consider supernatural events in their hypotheses. Why not? Because, as we saw with
Gosse’s Omphalos hypothesis, once you introduce the supernatural to a scientific hypothesis, there
is no way to falsify or test it. Once you introduce the untestable supernatural explanation, you
are no longer doing science—it’s a “science stopper.” We might want to say, “It is this way
because God willed it so” or “And then a miracle occurs” (fig. 1.1), and for some religious
people, that is all that need be said. But scientists are not allowed to do this, because it is
completely untestable and therefore outside the realm of science. If scientists do offer evi-
dence that falsifies the statement that “God did it this way,” do you think that fundamental-
ists would accept the evidence? As we will demonstrate throughout this book, the evidence
for evolution supplies just such a falsification, but creationists must deny it to salvage their
untestable hypotheses. Ironically, Johnson spends a whole chapter (chapter 5) in Darwin on
Trial talking about Karl Popper and the falsifiability criterion, but he completely misses the
point as to why it requires methodological naturalism for science to work in the first place.
In fact, there have been many scientific tests of supernatural and paranormal expla-
nations of things, including parapsychology, ESP, divination, prophecy, and astrology. All
of these nonscientific ideas have been falsified when subjected to the scrutiny of scientific
investigation (see Isaak 2006; also 2002 for a review). Johnson loudly complains that the
supernatural has been unfairly excluded from the debate, but this is clearly not true. Every
time the supernatural has been investigated by scientific methods, it has failed the test.
As Isaak (2002) put it,
Indeed, many supernatural explanations are rejected not because they are super-
natural but because they cannot or do not lead anywhere. It is possible to come up
with any number of possible explanations for anything—lost socks could be caused
by extradimensional vortices which our observations prevent from forming; hiccups