4 4 2C H A P T E R 2 0 ■ S c i e n t i f i c R e a s o n i n gessential protein, or if you suppose that the genetic material becomes shuf-
fled in a way that allows for differences in the rates at which proteins are
formed, it looks as though disaster will ensue. Crucial pieces will be missing,
or won’t be present in the right proportions, so that everything will break
down. How then could organisms with the pertinent structures or processes
have evolved from organisms that lacked them?
Behe offers numerous instances of molecular machines that, he claims,
could not have been built up in stages by natural selection. Among his most
influential examples is a discussion of devices that some bacteria use for
motion, flagella. He contrasts the bacterial flagellum with a different motor,
used by other cells, the cilium. “In 1973 it was discovered that some bacteria
swim by rotating their flagella. So the bacterial flagellum acts as a rotary
propeller—in contrast to the cilium, which acts more like an oar.”* Both flag-
ella and cilia are intricate structures, and Behe describes the many molecular
parts and systems that have to be present if they are to do their jobs. He con-
cludes that the complexity of the organization dooms any attempt to explain
its emergence as the result of natural selection. “As biochemists have begun
to examine apparently simple structures like cilia and flagella, they have dis-
covered staggering complexity, with dozens or even hundreds of precisely
tailored parts. It is very likely that many of the parts we have not consid-
ered here are required for any cilium to function in a cell. As the number
of required parts increases, the difficulty of gradually putting the system
together skyrockets, and the likelihood of indirect scenarios plummets.
Darwin looks more and more forlorn.”** Indeed, the most famous portraits
of Darwin hardly make him look exactly cheerful, but it’s worth asking why
examples like these should render him more forlorn.
Perhaps it seems obvious. Natural selection depends upon mutations that
are not produced in response to the organism’s needs. The bacteria are at
the mercy of chance, which will fling in this variant protein or that, with
negligible probability that the latest novelty will fit with what went before
or will contribute to the design project of building a flagellum. In essentials,
however, this is precisely parallel to an old creationist strategy, just the one
that Darwin sidestepped in the case of the eye. Behe has specified how the
intermediates are to be formed, and it isn’t surprising that his preferred sce-
nario has the air of impossibility.
What exactly is known about the bacterial flagellum? During the past
few decades, careful molecular studies have identified the genes that direct
the assembly of the motor, and have explored the ways in which it is put* Behe, Darwin’s Black Box, 70. Behe uses the example of the bacterial flagellum as a parade case
in many of his writings and presentations. See, for example, “Design at the Foundation of Life,”
in Science and Evidence for Design in the Universe (San Francisco, CA: Ignatius Press, 2000), 120 ff.
** Behe, Darwin’s Black Box, 73.97364_ch20_ptg01_423-448.indd 442 15/11/13 12:09 3M
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