Why internal states are important

Case study: agency in viruses?

Image of influenza virus.
Copyright Linda M. Stannard, Department of Medical Microbiology, University of Cape Town, 1995.

The phenomenon of phenotypic plasticity is perhaps the best prima facie candidate for agency in viruses. Phenotypic plasticity can be defined as the ability of organisms with the same genotype to vary their developmental pattern, phenotype or behaviour in response to varying environmental conditions (Ancel and Fontana, 2002).

A well-known case of phenotypic plasticity in viruses is the lysis-lysogeny decision, whereby parasitic lambda-phage viruses adopt a bet-hedging strategy in order to cope with fluctuations in the availability of their hosts (E. coli bacteria). When a virus invades a host bacterium, it may kill the host immediately by multiplying until the host's cell walls burst (lysis) or it remain quiescent and may confer immunity to infection upon its host (lysogeny). The strategy is described in detail in the Appendix. The important point is that the actual decision to invade or lie low is a random one, which depends entirely on thermal background noise. As one researcher puts it:

"...Thermal fluctuation at the molecular level makes for diversity in cells that start out under identical conditions," says Arkin. "The phage actually makes use of noise as a survival mechanism: sometimes it pays to multiply and infect as many hosts as possible, sometimes it pays to lie low. Either way, the viral population is prepared to cope with changing conditions" (cited in Preuss, 2000, italics mine).

Preuss's (2000) article describes the viral DNA as making a decision. Should we take this literally? If not, why not?

First, as the article states, it is random noise which determines whether the viral DNA is expressed or remains quiescent. It would be a misuse of the English language to describe this as a decision: decisions, by their very nature, require rational justification.

Second, the behaviour displayed by the viruses is in no way self-initiated: it is driven entirely by external environmental changes (thermal fluctuations). Before we can describe a piece of behaviour as a "decision", there has to be some kind of agency involved. At the very least, internal states of the organism (as well as external conditions) must influence the behaviour observed.

The foregoing discussion suggests two conclusions regarding the kind of behaviour in organisms that serves to identify intentional agency (and hence mental states):

A.1 Behaviour by an organism must vary in response to non-random internal states before it can be regarded as a manifestation of a mental state.

A.2 Behaviour by an organism must vary in response to its internal states, as well as external conditions, before it can be regarded as a manifestation of a cognitive mental state.