0. Abstract
Neuroscience aims to explain mental health problems as well
as provide other useful clinical information such as measuring severity and
predicting treatment response using nomothetic techniques which rely on type
identity. Davidson’s anomalous monism states that there is token identity but
not type identity for mental events. I will argue that evolution favours type identity
for at least some mental functions in hominids (including those likely to of
interest to clinical neuroscience such as anxiety) because natural selection
can only work through genetics replicating physical structures and processes. I
will discuss several possible defences of anomalous monism. Rejecting evolution
entirely as a theory creates too many problems and trying to argue evolution
has not influenced the development of the mind is unlikely to be true. The
concept of multiple realisation does not apply to minds belonging to evolution
of members of the same species. It may be that some aspects of mental
functioning have anomalous monism properties but others have been influenced by
evolution and have type identity properties and are accessible to neuroscience allowing
potential clinical utility for these techniques.
1.1
Anomalous monism’s challenge to the neuroscience
of mental health
Applied neuroscience has several goals in mental health. The first is explanation –
how do the mental states and events of clinical interest arise i.e. their
mechanisms which can lead onto methods of how to prevent undesirable mental
states and promote more desirable mental states and how to alter undesirable
mental states into more desirable ones (leaving aside whose values determine
desirability). Furthermore, if we have a better idea of the explanation of
mental states of clinical interest then we can change diagnostic criteria of
psychiatric disorders from mostly descriptive constructs to those based on
explanation.
A further goal of neuroscience in mental health is to
identify biomarkers which can have several clinical functions: assess risk of
developing a condition, in order to confirm a diagnosis or measure a trait, to
measure severity of a clinical state (which can also be used as a proxy marker
of treatment response), to identify the stage of someone’s illness , as a predictor
of treatment response and to help estimate prognosis (Davis et al, 2015 and
Steele & Paulus, 2019).
Are these goals of neuroscience possible according to
philosophy of mind? One influential position by Davidson outlines three
principles which all operate: “at least some mental events interact causally
with physical events” , that where causality exists it “will fall under strict
deterministic laws” and “there are no strict deterministic laws on the basis of
which mental events can be predicted and explained” (Davidson, 1970: 208). In
anomalous monism there is token identity of mental events/ states that is the mental
event/ state is also a physical event/ state (the physical state/event is the
token of the mental state/event in the physical realm). So, the mental event/ state supervenes on the
physical event/ state but it cannot be reduced to a physical state and any
examination of the physical event/ state will not allow a prediction of the
mental event/ state. Type identity of mental events/ states with physical
events/states means that you can predict the mental event/state from knowing
the physical event/state and that the equivalent mental event/state in
different individuals would be accompanied by the same physical event/ same in
them (as discussed in Heil, (2013A:128-130) but Davidson objects to
“psychophysical laws” applying between mental events/ states, as this would
lead to physical events/states having causal deterministic interactions with
each other and this would eliminate mental events/ states forming “reasons” for
behaviour such as thinking it is going to rain and taking an umbrella outside
as they are just the mental event/ state marker of the real deterministic
interactions at the physical level (Heil, 2013: 130-132) hence token identity
but no type identity.
Neuroscience especially in its application in mental
health clinical practice relies on nomothetic research methods. In other words
for a group of participants whose common principle is that they have a mental event/
state x (for instance depression, hallucinations or responding to a treatment) at
least some of them must have sufficient similarities in brain structure and/ or
processes which allows this similarity to be detected and demonstrated in
research participants and then extrapolated to patients in clinical practice. There
are formidable methodological difficulties for this type of clinical
neuroscience research (Steele & Paulus, 2019) even if type identity exists
but anomalous monism would a priori mean such research is impossible. There is
no type identity i.e. mental events/ states are not “reducible” to physical
events/states.
1.2
Is evolution involved in the development of the
human mind?
Davidson presents an ontological description of mind’s
relationship to the brain but how did the mind come about in humans - the ultimate
subject of interest of neuroscience in mental health? Evolution is the most
widely accepted theory explaining the development of physical human attributes
such as the eyes, the structure of cells or the functioning of the
cardiovascular system. Has evolution shaped the brain’s development and what
are the implications for the mind and anomalous monism?
Evolution is a process involving selection pressures that
preferentially favours certain attributes to be passed down to the next
generation in organisms if they allow them to produce more viable offspring.
This might be because this attribute (which may be discontinuous/ categorical
or a particular point on a spectrum such as increased length or a particular
colour) increases the lifespan of the organism (increasing the opportunity to
produce offspring) or increased fertility increasing the numbers of viable
offspring. Conversely certain attributes may be selected against because they
reduce the likelihood of viable offspring. This natural selection is a dynamic
process as the attributes’ advantage depends on its fit with the environment
which fluctuates through time.
A classic example are moths with a darker coloured variant –
this variant was more thought to be more easily spotted whilst resting on tree
barks by predators so tended to have shorter lifespans with subsequently less
offspring and was a rare variant. When the industrial revolution produced
pollution darkening tree barks which favoured the darker variant surviving by
being harder to spot against the dark bark then this dark variant became more
common.
Some attributes are selected for despite some disadvantages
because they offer some selection advantages such as sickle cell trait in
humans which can result in sickle cell disease but in the milder sickle cell
trait offers increased resistance to malaria a common dangerous endemic illness
in regions where sickle cell trait is commonly found.
A “Whiggish progress” view of evolution as continual
improvement ignores that fluctuating variation in attributes in response to
changing environments occurs through time. Whilst being aware of this tendency
there does appear to be a dramatic increase in brain size through time in
hominids. This bigger brain has survival costs – it requires a large proportion
of the body’s nutritional intake as energy to power its neural activity; it’s
lengthy maturation time requires many years of parenting and protection and the
large head combined with a bipedal gait tilting the pelvis increases
reproductive casualties dramatically for both mother and child in the form of
death and disease and associated impairment.
Given all these costs of the large brain through hominid
evolution what could be the gain in survival advantage or increased viable
offspring that justifies the selection of increasing brain size by evolutionary
forces? I will start by eliminating some brain functions as possibilities.
The brain has regulatory input into the cardiovascular and
respiratory systems but in humans there does not appear to be any impressive
additional abilities from the brain that would be favoured by evolution.
Control of the endocrine system resides in the hypothalamic-pituitary areas but
again there does not appear to be any human-specific evolutionary advantages.
None of these areas described above seem particularly enlarged in size.
The human cerebral cortex is dramatically enlarged. It is
involved in initiation and control of movement along with the basal ganglia and
cerebellum. Yet there is nothing particularly amazing about human movement such
as speed or agility compared to other species, the bipedal gait tends to make
us slower on the ground but it does free up our hands. Yes the hands are
capable of precision and manipulation but in the natural environment this does
not add up to much in terms of enhanced survival or increased viable offspring
by itself – the advantages come when the hands can be used to manipulate
objects created by people using the advantages created by the another function
which we shall discuss in the next paragraph. The cerebral cortex is also
involved in processing sensory perception but human senses are again not
outstanding compared to many other species to justify such an enlarged brain.
The final major brain function is to incorporate a variety
of data – external sensory perceptions, interoceptive information (such as
hunger), relevant past data such as memories, possible scenario planning/
anticipation of events and subsequent action and evaluation / responses (such
as emotions) . This evaluation of data (which may come from a variety of
locations in the brain) and then initiation of action takes place in the
cerebral cortex and involves the cerebellum and deeper ganglia such as the
amygdala. Given that the cerebral cortex is the part of the hominid brain that
has been greatly enlarged through evolution it seems likely that this function
is the evolutionary advantage that has been selected for – it has allowed us to
make tools, form complex societies and perform more advanced hunting, practice
agriculture and herding all of which increased our foodstuff availability
increasing survival and numbers of viable offspring. These brain functions may
be taken to be mind functions in many cases. A mind is “guided by representations”
(Heil 2013B, 138) – the various data the brain receives is converted into
representations and these guide actions. This is compatible with anomalous
monism (and also with type identity theories of mind states with brain states).
The rest of this section will proceed with the assumption of anomalous monism
or type identity.
Dennet classified several times of minds developed through
evolutionary processes as discussed by Heil (2013B:
138-40) - Darwinian minds react in
predictable ways to stable environments, next are Skinnerian minds learn
through trial and error to act in the most optimal ways in their environment, then
there are Popperian minds which create mental representations of their
environment to test internally to decide the optimal actions and finally
Gregorian minds are capable of self-conscious representation i.e. they are
conscious of themselves carrying out the representation. Animals with the more
advanced types of mind also contain in themselves the earlier types of minds.
So far only humans can be shown to have Gregorian minds but for example can
have their behaviour altered by operant conditioning as Skinnerian minds are. In
this case the evolutionary selection pressure seems to be increasing adaptive
capability of the organism whilst in their environment at least until the
Popperian to Gregorian transition.
One can ask though will evolution be involved in the mind? Using
Maslow’s hierarchy of needs with
“physiological needs” as an essential base of needs such as food and water and
then safety and security (I quibble with the order but that can be set aside
for now) then an organism that ignores these essential needs, for example does
not recognise when it needs to prioritise seeking food or water or does not
avoid danger is clearly at a risk of premature death reducing survival. An
organism that does not seek to create opportunities to reproduce is similarly
less likely to create viable offspring. Hence there will be selection pressures
to create brains that monitor interoceptive signals triggering scanning the
external environments for opportunities to seek to meet these physiological
needs or to monitor the environment for threats and respond appropriately.
So evolutionary processes exert selection pressures to
create brains and hence minds that can meet these needs. As a simple example it
is advantageous for organisms to have mental events such as “I am hungry
therefore I should seek food” which can also be understood as reasons for
behaviour. If higher levels of Maslow’s
needs (such as self-actualisation) can be shown to exert evolutionary positive
selection pressure then evolution will favour the development of brains and
hence minds that seek to meet that meet these minds. It is not necessary to
show all levels of need have an evolutionary input from an applied neuroscience
point of view just that evolution influences at least some brain/ mind
functions of clinical interest such as anxiety. I am not deploying an
expansionist evolutionary theory that all mind activity is influenced by
evolution – that the ability to write plays or fill out spreadsheets is all
down to natural selection – just that the neuroscience of mental health only
requires type identity for brain and mind states that have clinical usefulness
as discussed in 1.1.
1.3
The mechanism of evolution affecting the mind
and the challenge for anomalous monism
An example relevant to clinical neuroscience that has been
influenced by natural selection due to its usefulness increasing survival by
promoting avoidance of threatening situations is anxiety, the subject of a
recent set of editorials in the American Journal of Psychiatry (Cisler (2020),
Kalin (2020), Kessler (2020) and Smoller (2020)). They discussed how high
degrees of anxiety are common across many psychiatric disorders, it is an
evolutionary conserved mechanism, many different aspects of anxiety share
common genetic factors, that several neurological circuits that seem to perform
cross-species equivalent roles have been discovered in rodents, other primates
and humans and that neuroscience techniques can also be used for several roles
such as identifying common neural signatures of clinical problems or
investigating correlates of effective behaviour therapy. It does seem plausible
that anxiety would be influenced by natural selection.
If an organism lacked an anxiety response to threats it is
more vulnerable to shorter lifespan if it has no anxiety to drive avoidance of
predation or other dangers. Conversely too much anxiety will lead to excessive
inhibition of behaviour and passing up opportunities to seek food or seek mates
thus reducing lifespan or numbers of offspring. Thus, evolution is likely to
lead a variety of degrees of anxiety responses in a population with the
environment determining the appropriate level. Some anxiety disorders such as
phobias are clearly influenced by evolution – we tend to develop phobias to dangerous
situations that are part of our evolutionary inheritance (such as snakes,
spiders or situations where we can be pounced upon such as busy spaces) rather
than contemporary dangerousness (such as guns). Other mental disorders often
generate anxiety (for example persecutory delusions) which will then involve
anxiety mechanisms influenced by evolution.
For natural selection to have a positive selection pressure
for attributes it relies on the organism with the advantageous attribute to
pass it on to their offspring -fidelity of replication. (A negative selection
pressure will be where the trait is disadvantageous for survival or having less
viable offspring and so there is less offspring carrying this trait). The
attributes or traits are passed on by genetic transmission. For genetic
transmission though to act as the mechanism by which natural selection is
carried out then it requires the advantageous trait or attribute to be largely
replicated in the offspring from the parent organism. If the alteration in
kidney structure or the modification in the clotting process enhances an
organism’s survival, then this is what needs to be passed on to its offspring.
So genetic material must produce a similar copy in offspring. If there is no
similarity then natural selection cannot work – if an attribute is advantageous
but is not passed on by producing similar structure and or process in the
offspring then it is only advantageous in the generation of organism it arose
in and stops there. This would mean evolution would not occur as there is no
mechanism through which advantages could be passed on.
Genetics works primarily through DNA sequences being
translated into amino acid sequences and hence proteins. These proteins then
lead to structural and/ or process changes directly or indirectly. Proteins are
biological and hence physical in nature and so are any results of their
influence and thus potentially accessible to scientific measurement. There is no evidence of genetic transmission
of non-physical material. This means that if a mental function is affected by
evolution – and it seems likely that at least some mental functions (discussed in
1.2 and anxiety earlier in this section) will be affected by evolution
– then genetic transmission will be expected to create a close similarity in
structure and/ or processes between parent and offspring such as an organised
neurological circuit or altered levels of neurotransmitter activity. This close
similarity for inherited structure and process has to lead to similarities in
mental function (i.e. type identity) which is the attribute being selected for.
If the structure/ process being inherited does not lead to similarity in mental
function then natural selection will not be able to take place and in 1.2 there is strong evidence to suggest
natural selection in hominids has favoured the development of mental functions
such that are found in current humans. Natural
selection therefore means type identity for at least the mental functions
influenced by natural selection thus opening the door to neuroscientific
investigations for them.
It may be that some mental functions are replicated as a
capability and other factors then build upon a common underlying structure
(such as a distributed circuit) to produce final mental end-products (perhaps
between individuals they have very different connections between neurones and
consequent activity). For mental functions though that are more basic to
survival and evolutionarily conserved in species that there is greater fidelity
of replication as natural selection is unlikely to rely on a more haphazard
arrangement or indeed that this haphazard arrangement to be conserved.
Clinical neuroscience does not need to be able to explain
the production of all mental contents of mental health problems to be useful,
for example they can used as a diagnostic marker or to measure illness severity
(see 1.1). Depression can affect mental functions likely to be influenced
by natural selection such as appetite, sleep regulation and ability to
concentrate – neuroscience could be used to measure severity of the impact of
depression on these functions. Anxiety disorders are often maintained by
operant conditioning and this Skinnerian mind function has been developed
through natural selection Heil (2013B: 138-40) then clinical neuroscience has
the possibility of demonstrating the neural signature of these processes.
Hallucinations are a perception without an appropriate stimulus and are found
in several types of mental health problems – these to some degree involve
mental functions involving perception to some extent which will have been
influenced by natural selection which gain implies type identity for these
processes again opening the door to clinical neuroscience.
2.1 Defending anomalous monism against evolution’s challenge
Several counter arguments can be deployed to fend off
this challenge. Firstly, one can assert that that evolution is only a theory and
reject it out of hand. This causes multiple difficulties – why are so many
biologists wrong about a theory that seems to have much usefulness it leaves
the problem of how did species come about and their similarities and
differences? If we resort to creationist theories we could equally be opening
the door to occasionalism and anomalous monism is lost by the back door.
Secondly, evolution may be accepted but it may be argued
that it does not apply to the mind. The
mental functions that we may regard as comprising the mind (such as
consciousness in the broad sense, abstract thought, emotions, memories) may be an accidental
by-product of evolution: a spandrel - “by-products of the development of other
traits, but they themselves have never possessed any adaptive function” (Murphy
& Woolfolk, 200: p.243). Yet as discussed in 1.2. this argument it
has several difficulties. What are these other traits that the mind got a free
ride on? What else could explain the investment in increasing brain size in
hominids as other possibilities seem unlikely? How did the mind develop in
humans if not through evolutionary processes?
The third argument is that multiple realisation for analogous
structures/ functions occurs due to evolution (such as eyes in insects,
cephalopods and vertebrates) means no type identity is required for mental
functions but multiple realisation applies to different species or even alien
species or different types of entities such as computers with artificial intelligence
having similar functions to mental functions of human minds. This however does
not apply to members of the same species and at least some mental functions
such as pain are likely to be based on “uniform physical processes” in humans
(Papineau 2010: 189-190). Clinical
neuroscience is ultimately interested in the human species not aliens or Robbie
the Robot.
The argument can be further developed for example that
some higher mental functions such as problem solving and learning capabilities may
be “variably realized at the physical level across different individuals” even
if these capabilities are selected for by evolution (Papineau, 2010: 186-187). The
division between mind functions with evolutionary input and type identity (such
as anxiety) and those with evolutionary input but only for a “variably
realised” capability (such as a problem solving capability) or mental functions
with no evolutionary input (such as the ability to write a novel) may appear
conceptually “reasonably clear-cut, but on reflection it is by no means obvious
where it lies” (Papineau, 2010: 191). This analysis is compatible with Heil’s
analysis of Davidson’s position – that the “mental events” Davidson is
referring to are only a subset of particular activities of the mind such as
sentences involving propositional attitudes (Heil 2013A: 133-137). So a
capability for certain mental functions may show type identity to a certain degree
but the final realisation – altered by culture or experience – may be more
“variably realised” (see discussion in 1.3 about common circuits between
individuals but different connections between neurones within these circuits).
To use dreaded computer analogies acknowledging this is a
metaphorical not exact comparison it may be that evolution could be thought of
as creating the hardware and operating system (though the system settings may
be influenced by the particular environment the organism is in) and this
operating system allows a form of self-created programs to be made or the
programs to be created by external inputs (the metaphorical programmer of the
mind would be experience and meaning or extra-individual factors such as
sociological factors): these programs in themselves are not influenced by
evolution, but the capacity for these to be created were influenced by
evolution. Since the operating system and hardware is influenced by evolution
this allows type identity and a possible target of investigation by
neuroscience using nomothetic techniques. The programs running on the operating
system on the other hand, whilst using the operating system, can follow
Davidson’s anomalous monism principles and are not able to investigated by
neuroscience using nomothetic techniques. These programs may be regarded as
operating on a “different level” and be investigated and described using other
techniques such as qualitative research and schools of knowledge such as
non-reductive psychology or sociology (Thornton, 2015). So whilst the higher
level of thought triggering anxiety (“people are going to laugh at me because I
look vulnerable”) may have a token identity and be inaccessible to neuroscience
but the associated threat response is realised through anxiety neurological
circuits which show type identity and are accessible to neuroscience.
3.1 Conclusion
Davidson’s anomalous monism involves token identity and no
psychophysical laws for mental events but not type identity which would make
neuroscience for mental health problems using nomothetic techniques impossible.
Evolution is likely to have favoured the development of increased brains in
hominids and these are likely to be for mental functions. Evolution requires
the replication of structures and processes in the next generation which
necessitates type identity for at least some mental functions. A metaphorical
model of the computer hardware and operating system being influenced by
evolution and hence having type identity for some mental functions and
accessible to neuroscience using nomothetic techniques and programs whose
outputs may have token identity but not type identity which would be the
equivalent of Davidson’s mental events and better investigated with other
methods.
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