Is Biology Reducible to the Laws of Physics?
Darwinian Reductionism: Or, How to Stop Worrying and Love
Molecular Biology. Alex Rosenberg. x + 263 pp. University
of Chicago Press, 2006. $40.
Alex Rosenberg is unusual among philosophers of biology in adhering
to the view that everything occurs in accordance with universal
laws, and that adequate explanations must appeal to the laws that
brought about the thing explained. He also believes that everything
is ultimately determined by what happens at the physical
level—and that this entails that the mind is "nothing
but" the brain. For an adherent of this brand of physicalism,
it is fairly evident that if there are laws at "higher"
levels—laws of biology, psychology or social
science—they are either deductive consequences of the laws of
physics or they are not true. Hence Rosenberg is committed to the
classical reductionism that aims to explain phenomena at all levels
by appeal to the physical.
It is worth mentioning that, as Rosenberg explains, these views are
generally assumed by contemporary philosophers of biology to be
discredited. The reductionism that they reject, he says,
holds that there is a full and complete explanation of
every biological fact, state, event, process, trend, or
generalization, and that this explanation will cite only the
interaction of macromolecules to provide this explanation.
Such views have been in decline since the 1970s, when David Hull
(The Philosophy of Biological Science ) pointed
out that the relationship between genetic and phenotypic facts was,
at best, "many/many": Genes had effects on numerous
phenotypic features, and phenotypic features were affected by many
genes. A number of philosophers have elaborated on such difficulties
in subsequent decades.
The question then is whether Rosenberg's latest book, Darwinian
Reductionism: Or, How to Stop Worrying and Love Molecular
Biology, constitutes a useful attack on a dogmatic orthodoxy or
merely represents a failure to understand why the views of an
earlier generation of philosophers of science have been abandoned.
Unfortunately I fear the latter is the case. More specifically, his
portrayal of the genome as a program directing development, which is
the centerpiece of his reductionist account of biology, discloses a
failure to appreciate the complex two-way interactions between the
genome and its molecular environment that molecular biologists have
been elaborating for the past several decades.
In earlier work, Rosenberg accepted the consensus among philosophers
of biology that biology couldn't be reduced to chemistry or physics.
But whereas most philosophers saw this as a problem for philosophy
of science, and for traditional models of reduction, Rosenberg
concluded that it was a problem for biology, a problem indicating
that the field's purported explanations were neither fundamental nor true.
However, in his most recent book Rosenberg is more sanguine about
biology. As the title suggests, the new idea is that recognition of
the pervasiveness of Darwinism in biology will enable us to assert
reductionism after all. Rosenberg is an admirer of Dobzhansky's
famous remark that nothing in biology makes sense except in the
light of evolution:
Biology is history, but unlike human history, it is history
for which the "iron laws" of historical change have been
found, and codified in Darwin's theory of natural selection. . . .
[T]here are no laws in biology other than Darwin's. But owing to the
literal truth of Dobzhansky's dictum, these are the only laws
The suggestion is that something Rosenberg calls "the principle
of natural selection" is actually a fundamental physical law.
Natural selection, according to him, is not a statistical
consequence of the operation of many other physical (or perhaps
higher-level) laws, as most philosophers of biology believe. Rather,
it is a new and fundamental physical law to be added to those
already revealed by chemistry and physics. I won't try to recount
Rosenberg's arguments for this implausible position.
The largest part of the book motivates reductionism from a quite
different direction by defending the view that genes literally
embody a program that produces development. Rosenberg introduces
this view by recounting some work on the development of insect
wings. There is a rather disturbing tendency in this exegesis to
suggest an imputation of agency to the genes that are implementing
this program. He says that the genes fringe and
serrate "form the wing margin," for example, and
"wingless builds wings." He also maintains that
in Drosophila, "2500 genes . . . are under direct or
indirect control of eyeless." As the last two examples
illustrate and Rosenberg explains, genes are frequently identified
by what doesn't happen when they are deleted. But Rosenberg seems
quite untroubled by the dubious inference from what doesn't happen
to the conclusion that making this happen is what the genes
"do" when in place. These reifications provoke a range of
worries, but at a minimum, a defense of such ways of speaking will
need to address another growing philosophical consensus to which
Rosenberg is an exception, that the gene is a concept that no longer
has an unproblematic place in contemporary biology.
Rosenberg does attempt a defense of the gene, but his arguments are
unconvincing. The biggest problem is that he never says what he
means by a gene. He refers uncritically to estimates of the number
of genes in the human genome; although he does outline some of the
difficulties with these estimates, he does not seem to appreciate
their force. As a positive contribution, it appears that all he has
to offer is the proposal that genes are "sculpted" out of
the genome by natural selection to serve particular functions. The
central point of critics of the gene concept is that functional
decomposition identifies multiple overlapping and crosscutting parts
of genomes. The "open reading frames" to which biologists
refer when they count the genes in the human genome not only can
overlap but are sometimes read in both directions. Subsequent to
transcription they are broken into different lengths, edited,
recombined and so on, so that one "gene" may be the
ancestor of hundreds or even thousands of final protein products.
Sophisticated would-be reductionists, such as Kenneth Waters, have
tried to accommodate this point. Rosenberg seems just to ignore it
as happily as he ignores most of the literature that has expounded
the difficulties (for example, What Genes Can't Do, by
Lenny Moss , and The Concept of the Gene in Development
and Evolution, edited by Peter Beurton, Raphael Falk and
Hans-Jörg Rheinberger ).
The problem might have been ameliorated if Rosenberg had paid more
attention to the increasingly diverse constituents recognized in the
genome apart from the genes he needs to run his programs. The lack
of concern with the genome is highlighted, for example, when in the
course of a single paragraph he says that sculpting of the genome by
natural selection has resulted in "a division mainly into
genes" and refers to 95 percent of the human DNA sequence
appearing to be "mere junk" (another hypothesis that has
been widely rejected). It is conceivable that Rosenberg means to
define genome so as to exclude the junk, although I have
never encountered such a usage before. What is clear, though, is
that he sees the genome merely as a repository for the
informationally conceived genes supposed to run the developmental
program. Attention to the increasingly understood complexities of
the genome as a material object would have made the misguided nature
of the enterprise much clearer.
A further problem is that some of the biology in the book is dated.
For example, Rosenberg says that "there are about 30,000 to
60,000 genes in our genome," but in fact there is a fairly
stable consensus now that the number is about 23,000. More striking
is his remark that alternative splicing is "uncommon but not
unknown," whereas it is actually widely accepted that such
splicing occurs in more than 70 percent of human genes. Although
Rosenberg has researched some biological topics in detail, the book
contains other lapses as well. He appears to be unaware, for
instance, that methylation occurs in contexts other than sexual
imprinting. And I was struck by his remark that the world is now
mainly populated by sexual species; in fact, the overwhelming
majority of organisms now, as ever, are prokaryotes and (relatively)
simple asexual eukaryotes. It is admittedly difficult or impossible
to stay fully au courant with the latest in molecular
biology, but a careful reading of the manuscript by a practitioner
would have been very helpful.
Because I have been involved for many years in criticism of the
earlier orthodoxy that Rosenberg continues to defend, it is not
surprising that I am unconvinced by his reactionary argument. And it
is of course very often a good thing for philosophers to confront
the orthodoxies of their discipline. But the standards for
undermining orthodoxy are inevitably high, and Rosenberg does not
come close to meeting them.
The subtitle invites us to learn to love molecular biology. Many of
the philosophers whom Rosenberg's views contradict greatly admire
the achievements of molecular biology. Love, however, is well known
for being blind. I would encourage Rosenberg to settle for admiration.