4 4 3S c i e n t i f i c R e v o l u t i o n stogether in the development of an individual bacterium. Some mutations
in these genes allow for bacteria to move, albeit less efficiently. What is cur-
rently missing, however, is that systematic study of the differences among
bacteria with flagella and bacteria without that would parallel the knowl-
edge attained in the case of vision. A sufficiently intensive study of the ge-
nomes of bacteria that lack flagella would enable biologists to explore the
potential role of some of the crucial genes, and of the proteins they give rise
to, when others are absent, and thus enable them to make more progress
with Behe’s apparently formidable challenge.
Most sciences face unsolved problems—indeed the exciting unsolved
problems are the motivators for talented people to enter a field. Chemists
still struggle to understand how newly made proteins fold into their three-
dimensional shapes as they are synthesized. To take an instance closer to
hand, Behe’s own discussion acknowledges that there’s still a lot to learn
about the molecular structure and functions of cilia. Unsolved questions are
not typically written off as unsolvable—nobody proposes that there’s some
special force, unknown to current chemistry (an “intelligent force” perhaps?)
that guides the proteins to their proper forms, or some hand that assembles
the cilium in the development of an individual bacterium. Why, then, should
we believe that the problem of the bacterial flagellum is unsolvable? Just be-
cause, in the absence of systematic molecular studies of bacteria with and
without flagella, we can’t currently give a satisfactory scenario for the evolu-
tion of the bacterial flagellum under natural selection, why should we con-
clude that further research couldn’t disclose how that evolution occurred?
We are beguiled by the simple story line Behe rehearses. He invites us
to consider the situation by supposing that the flagellum requires the in-
troduction of some number—20, say—of proteins that the ancestral bacte-
rium doesn’t originally have. So Darwinians have to produce a sequence of
21 organisms, the first having none of the proteins, and each subsequent
organism having one more than its predecessor. Darwin is forlorn because
however he tries to imagine the possible pathway along which genetic
changes successively appeared, he appreciates the plight of numbers 2–20,
each of which is clogged with proteins that can’t serve any function, pro-
teins that interfere with important cellular processes. These organisms will
be targets of selection, and will wither in the struggle for existence. Only
number 1, and number 21, in which all the protein constituents come
together to form the flagellum, have what it takes. Because of the dreadful
plight of the intermediates, natural selection couldn’t have brought the bac-
terium from there to here.
The story is fantasy, and Darwinians should disavow any commitment to
it. First, there is no good reason for supposing that the ancestral bacterium
lacked all, or even any, of the proteins needed to build the flagellum. It’s a
common theme of evolutionary biology that constituents of a cell, a tissue,
or an organism are put to new uses because of a modification of the genome.97364_ch20_ptg01_423-448.indd 443 15/11/13 12:09 3M
some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materiallyCopyright 201^3 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights,
affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.