Reduction and Elimination in Philosophy and the Sciences

Are Lamarckian Explanations Fully Reducible to Darwinian ones? The Case of “Directed Mutation” in Bacteria — Davide Vecchi
environmental factors are irrelevant to mutational
responses (it has been established that there exist very
specific processes of mutational response triggered by
environmental stresses like starvation), nor on the
hypothesis that there is no targeting of specific genomic
regions, while growing evidence is accumulating in favour
of seeing mutational responses as evolved adaptive
responses of the organism. What can be safely said today
is that random variation is not the norm. Mutational
processes are highly biased and targeted affairs. Still, can
a revised and softened version of Darwinism suffice to
dispel the ghost of Lamarck? As Hall (1998) argues,
adaptive mutation is a different process from growthdependent
or “normal” bacterial mutation, even though it
clearly is a Darwinian process. The important questions on
this score are: how is the hypermutation state triggered? Is
it triggered by the environmental stress or by the selective
pressure? Is it regulated by specific genes, or rather by
some unspecified and unknown, possibly innate, capacity
of the organism? We still don’t know. For the same
reasons, I contend, we cannot answer the question of
whether we need an explanation of HSH in terms couched
via the language of intentionality and choice, or whether a
Darwinian explanation couched in terms of chance and
selection is all we need. Or so I will argue.
It could be argued that the phenomenon of adaptive
mutagenesis is purely Darwinian. From this perspective it
could be asked: what does the Lamarckian language of
intentionality, purpose and choice add to explanations
concerning adaptive mutations? Nothing is the answer:
Lamarckian concepts are simply redundant. To say that
organisms choose to mutate in particular ways, that they
deliberately try to reach a particular adaptive goal, that
they intend to change and adapt in specific ways, is
equivalent to invite inappropriate teleological talk. Even
though emphasis on the phenomenon has highlighted the
need to discriminate between mutations with different
characteristics concerning their basic properties
(environmental conditions, time and site of occurrence), it
is clear that the directional outcome is a product given by
the extreme reduction of design search space, by the
temporal and local increase in efficiency of the search, and
by a more general strategy of mutation rate increase.
A variant of the same dismissive attitude could
instead stress that instead of explanatory redundancy
(based on the application of Ockham’s razor), Lamarckian
explanations are reducible to Darwinian ones. This would
vindicate the hypothesis that Darwinism is a more
fundamental process than Lamarckism. In fact, it seems
that the “intentionality” of Lamarckian systems like those
supposedly governing adaptive mutational responses must
arise either by means of the cumulative effects of past
natural selection acting on ultimately random mutations, or
more simply by a more error-prone pathological response
of cells. Therefore the epistemic reducibility of Lamarckian
explanations seems to be achievable. So, even though the
orthodox and hardened Neo-Darwinian views on directed
mutation has been revised and updated, the revision of the
Darwinian view has not touched certain residual and
crucial elements constitutive of some meaning of
“randomness”, which make an appeal to the Lamarckian
language of intentionality inappropriate. This alternative
seems to illustrate the sensible view shared by most
practitioners.
However, I think that this epistemological move
cannot shed any light on the ontological issue pertaining to
the nature of mutation, and on the basic question concerning
the existence of genuine Lamarckian processes.
What could a genuine Lamarckian phenomenon be like?
Genuine intentionality would perhaps involve the
preferential environmental induction of useful and
beneficial mutations, which is not happening, or the
targeting of specific genes, which is still quite controversial.
But an equally promising avenue would be to consider
genuine intentionality as involving the choice of starved
and stresses cells to enter the hypermutation state. I think
that at this juncture lies the best chance to vindicate some
genuine Lamarckian credentials. If the hypermutation state
is triggered by some as yet unspecified and unknown
capacity of the organism, then Lamarckism could be
vindicated. Or better it would be if we were unable to find a
mechanistic basis for the cell response.
Intentionality does not seem to be needed to provide
explanations that save the known phenomena of adaptive
mutagenesis. Still, this could be simply appearance. The
crucial question remains: how do we explain the fact that
only a subpopulation of bacteria hypermutates? It seems
that some element in the environment triggers such a
state, or perhaps it is a cell that chooses to do so? Where
is the evidence in favour of the first “mechanical”
hypothesis? And is the first hypothesis simpler than the
second? And why is it simpler to hypothesise that the
bacterium senses an environmental signal rather than
hypothesising that it chooses to hypermutate? In the first
case we need a sensory mechanism, in the second just
agency of some kind. Furthermore, even a sensory
mechanism could be sufficient to phagocyte a slice of the
intentional cake.
The position of the reductionist and materialist rests
on the adoption of the argument from parsimony. But
voiced have been raised to argue against this adoption of
Ockham’s razor, and against a more general ontological
conservatism (Sober 2001), especially when the
intentionality hypothesis is ontologically as economical as
the alternatives. The issue is that as there are no
arguments in favour of the reification of intentionality as a
distinct and emergent quality, so there are no arguments
against.
So it could be that the more one digs into the
subject the more the Lamarckian language of choice
makes sense. In this sense it is not enough to point out
that polymerase IV and the down regulation of MMR are
involved in the process of hypermutation, that is, an errorenhancing
and a less efficient error-editing process. The
question remains of what triggers the state, of whether it is
the bacterium that “decides” to hypermutate.
Also note that in many ways a panpsychist
hypothesis, with the postulation of all its monads, is not
clearly more complex and therefore amenable to be
chopped off with one stroke of Ockham’s razor. Even
bacterial chemotaxis is nowadays described somehow in
terms of cells’ intentionality (cells are analogised to
nanobrains). The panpsychist perspective according to
which intentionality is everywhere remains simpler that any
emergentist view. If mentality and intentionality are basic
and primitive, then ascriptions of mentality are, despite the
risk of anthropomorphism, always justifiable. The idea that
there exists a continuum of levels of intentionality, rather
than an abrupt emergence of something totally new,
remains appealing.
The great appeal of the Darwinian account (e.g.
based on a blind variation and selective retention formula)
is that it offers a very general mode of explanation, and a
clear recipe to dispense of epiphenomenal intentionality
(Hull 1988). The active agent easily disappears from
selectionist accounts. But can we get rid of agency so
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