of consciousness. Why, and in what sense, was it necessary to develop
something like consciousness in the nervous systems of animals?
Couldn’t zombies have evolved instead? Here, the answer is both yes
and no.
As I noted in the Introduction, conscious experience is not an all-ornothing
phenomenon; it comes in many shades and flavors. There is a
long history of consciousness on this planet. We have strong, converging
evidence that all of Earth’s warm-blooded vertebrates (and probably
certain other creatures) enjoy phenomenal experience. The basic brain
features of sensory consciousness are preserved among mammals and
exhibit strong homologies due to common ancestry. They may not have
language and conceptual thought, but it is likely that they all have sensations
and emotions. They are clearly able to suffer. But since they do all
this without verbal reports, it is almost impossible to investigate this issue
more deeply. What we must understand is how Homo sapiens managed
to acquire—over the course of our biological history and
individually as infants—this amazing property of living our lives in the
Ego Tunnel successfully and without realizing it. First, let’s not forget that evolution is driven by chance, does not
pursue a goal, and achieved what we now consider the continuous optimization
of nervous systems in a blind process of hereditary variation
and selection. It is incorrect to assume that evolution had to invent
consciousness—in principle it could have been a useless by-product.
No necessity was involved. Not everything is an adaptation, and even
adaptations are not optimally designed, because natural selection can
act only on what is already there. Other routes and solutions were and
remain possible. Nevertheless, a lot of what happened in our brains and
in those of our ancestors clearly was adaptive and had survival value.
Today, we have a long list of potential candidate functions of consciousness:
Among them are the emergence of intrinsically motivating
states, the enhancement of social coordination, a strategy for improving
the internal selection and resource allocation in brains that got too
complex to regulate themselves, the modification and interrogation of
goal hierarchies and long-term plans, retrieval of episodes from longterm
memory, construction of storable representations, flexibility and
sophistication of behavioral control, mind reading and behavior prediction
in social interaction, conflict resolution and troubleshooting, creating
a densely integrated representation of reality as a whole, setting a
context, learning in a single step, and so on. It is hard to believe that
consciousness should have none of these functions. Consider one example
only.
There is a consensus among many leading figures in the consciousness
community that at least one of the central functions of phenomenal experience
is making information “globally available” to an organism. Bernard
Baars’s global-workspace metaphor has a functional aspect: Put simply,
this theory says that conscious information is that subset of active information
in the brain that requires monitoring because it’s not clear which
of your mental capacities you will need to access this information next.
Will you need to direct focal attention at it? Will you need to form a concept
of it, to think about it, to report it to other human beings? Will you
need to make a flexible behavioral response—one that you have selected
and weighed against alternatives? Will you need to link this information to episodic memory, perhaps in order to compare it with things you
have seen or heard before? Part of Baars’s idea is that you become conscious
of something only when you don’t know which of the tools in
your mental toolbox you’ll have to use next.
Note that when you learn a difficult task for the first time, such as tying
your shoes or riding a bicycle, your practicing is always conscious. It
requires attention, and it takes up many of your resources. Yet as soon as
you’ve mastered tying your shoes or riding a bicycle, you forget all about
the learning process—to the point that it becomes difficult to teach the
skill to your children. It quickly sinks below the threshold of awareness
and becomes a fast and efficient subroutine. But whenever the system is
confronted with a novel or challenging stimulus, its global workspace is
activated and represented in consciousness. This is also the point when
you become aware of the process.
Of course, a much more differentiated theory is needed, because
there are degrees of availability. Some things in life, such as the ineffable
shade of Green No. 25, are available for attention, say, but not for memory
or conceptual thought. Other things are available for selective motor
control but are accessed so quickly you don’t really attend to them: If
100-yard sprinters were to wait until they consciously heard the starter’s
shot, they would already have lost the race; fortunately, their body hears
it before they do. There are many degrees of conscious experience, and
the closer science looks, the more blurry the border between conscious
and unconscious processing becomes. But the general notion of global
availability allows us to tell a convincing story about the evolution of
consciousness. Here is my part of the story: Consciousness is a new kind
of organ.
Biological organisms evolved two different kinds of organs. One
kind, such as the liver or the heart, forms part of an organism’s “hardware.”
Organs of this type are permanently realized. Then there are “virtual
organs”—feelings (courage, anger, desire) and the phenomenal
experience of seeing colored objects or hearing music or having a certain
episodic memory. The immune response, which is realized only
when needed, is another example of a virtual organ: For a certain time, it
creates special causal properties, has a certain function, and does a job for the organism. When the job is done, it disappears. Virtual organs are
like physical organs in that they fulfill a specific function; they are coherent
assemblies of functional properties that allow you to do new things.
Though part of a behavioral repertoire on the macro level of observable
traits, they can also be seen as composed of billions of concerted microevents—
immune cells or neurons firing away. Unlike a liver or a heart,
they are realized transiently. What we subjectively experience are the
processes brought about by the ongoing activity of one or many of such
virtual organs.
Our virtual organs make information globally available to us, allowing
us to access new facts and sometimes entirely new forms of knowledge.
Take as an example the fact that you are holding this book in your hands
right now. The phenomenal book (i.e., the conscious book-experience)
and the phenomenal hands (i.e., the conscious experience of certain parts
of a bodily self) are examples of currently active virtual organs. The neural
correlates in your brain work for you as object emulators, internally
simulating the book you are holding, without your being aware of the
fact. The same is true of the conscious hand-experience, which is part of
the bodily subject emulator. The brain is also making other facts available
to you: the fact that this book exists, that it has certain invariant surface
properties, a certain weight, and so on. As soon as all this information
about the existence and properties of the book becomes conscious, it is
available for the guidance of attention, for further cognitive processing,
for flexible behavior.
Now we can begin to see what the central evolutionary function of
consciousness must have been: It makes classes of facts globally available
for an organism and thereby allows it to attend to them, to think
about them, and to react to them in a flexible manner that automatically
takes the overall context into account. Only if a world appears to you in
the first place can you begin to grasp the fact that an outside reality exists.
This is the necessary precondition for discovering the fact that you
exist as well. Only if you have a consciousness tunnel can you realize
that you are part of this reality and are present in it right now.
Moreover, as soon as this global stage—the consciousness tunnel—
has been stabilized, many other types of virtual organs can be generated and begin their dance in your nervous system. Consciousness is an inherently
biological phenomenon, and the tunnel is what holds it all together.
Within the tunnel, the choreography of your subjective life
begins to unfold. You can experience conscious emotions and thereby
discover that you have certain goals and needs. You can apprehend
yourself as a thinker of thoughts. You can discover that there are other
people—other agents—in the environment and learn about your relationship
to them; unless a certain type of conscious experience makes
this fact globally available to you, you cannot cooperate with them, selectively
imitate them, or learn from them in other ways. If you are
smart, you may even begin to control their behavior by controlling their
conscious states. If you successfully deceive them—if, say, you manage
to install a false belief in their minds—then you have activated a virtual
organ in another brain.
Phenomenal states are neurocomputational organs that make survivalrelevant
information globally available within a window of presence.
They let you become aware of new facts within a unified psychological
moment. Clearly, being able to use all the tools in your mental toolbox
to react to new classes of facts must have been a major adaptive advantage.
Every new virtual organ, every new sensory experience, every new
conscious thought had a metabolic price; it was costly to activate them,
if only for a couple of seconds or minutes at a time. But since they paid
for themselves in terms of additional glucose, and in terms of security,
survival, and procreation, they spread across populations and sustain
themselves to this day. They allowed us to discriminate between what
we can eat and what we can’t, to search for and detect novel sources of
food, to plan our attack on our prey. They allowed us to read other
people’s minds and cooperate more efficiently with our fellow hunters.
Finally, they allowed us to learn from past experience.
The interim conclusion is that making a world appear in an organism’s
brain was a new computational strategy. Flagging the dangerous
present world as real kept us from getting lost in our memories and our
fantasies. Flagging the present enables a conscious organism to plan
different and more efficient ways of escape or of deceiving or stalking
its prey, namely by comparing internal dry runs of the target behavior with the features of a given world. If you have a conscious, transparent
world-model, you can, for the first time, directly compare what is actual
with what is only possible, the actual world with simulated possible
worlds you’ve designed in your mind. High-level intelligence means
not only having offline states in which you can simulate potential
threats or desired outcomes but also comparing the real situation with
a number of possible goal-states. After you have found a path from the
real world into the most desirable possible world in your mind, you
can begin to act.
It is easy to overlook the causal relevance of this first evolutionary
step, the fundamental computational goal of conscious experience. It is
the one necessary functional property on which everything else rests.
We can simply call it “reality generation”: It allowed animals to represent
explicitly the fact that something is actually the case. A transparent
world-model lets you discover that something is really out there, and by
integrating your portrait of the world with the subjective Now, it lets
you grasp the fact that the world is present. This step opened up a new
level of complexity. Thus, having a global world-model is a new way of
processing information about the world in a highly integrated manner.
Every conscious thought, every bodily sensation, every sound and every
sight, every experience of empathy or of sharing the goals of another human
being makes a different class of facts available for the adaptive, flexible,
and selective form of processing that only conscious experience can
provide. Whatever is elevated to the level of global availability suddenly
becomes more fluid and more context-sensitive and is directly related to
all other contents of your conscious mind.
The functions of global availability can be specific: Conscious color
vision gives you information about nutritional value, as when you notice
the luscious red berries among the green leaves. The conscious experience
of empathy provides you with a nonlinguistic form of knowledge
about the emotional states of a fellow human being. Once you have this
form of awareness, you can attend to it, adapt your motor behavior to it,
and associate it with memories of the past. Phenomenal states do not just
represent facts about berries or about the feelings of other human beings;
they also bind these things into a global processing stage and allow you to use all your mental capacities to explore them further. In short,
individual conscious experiences from the object level upward are virtual
organs that transiently make knowledge available to you in an entirely
new data format—the consciousness tunnel. And your unified
global model of a single world provides a holistic frame of reference in
which all this can take place.
If a creature such as Homo sapiens evolves the additional ability to
run offline simulations in its mind, then it can represent possible
worlds—worlds that are not experienced as present. This species can
have episodic memory. It can develop the ability to plan. It can ask itself,
“How would a world look in which I had many children? What would
the world be like if I were perfectly healthy? Or if I were rich and famous?
And how can I make these things happen? Can I imagine a path
leading from the present world into this imagined world?”
Such a being can also enjoy mental time travel, because it can switch
back and forth between “inside-time” and “outside-time.” It can compare
present experiences to past ones—but it can also hallucinate or get lost
in its own daydreams. If it wants to use these new mental abilities properly,
its brain must come up with a robust and reliable way to tell the difference
between representation and simulation. The being must stay
anchored in the real world; if you lose yourself in daydreams, sooner or
later another animal will come along and eat you. Therefore, you need a
mechanism that reliably shows you the difference between the one real
world and the many possible ones. And this trick must be achieved on
the level of conscious experience itself, which is not an easy problem. As
I discussed, conscious experience already is a simulation and never
brings the subject of experience—you—into direct contact with reality.
So the question is, How can you avoid getting lost in the labyrinth of
your conscious mind?
A major function of the transparent conscious model of reality is to
represent facticity—that is, to generate a rock-bottom frame of reference
for the organism using it: something that unfailingly defines what is
real (even if it isn’t); something you cannot fool around or tamper with.
Transparency solved the problem of simulating a multitude of possible inner worlds without getting lost in them; it did so by allowing biological
organisms to represent explicitly that one of those worlds is an actual
reality. I call this the “world-zero hypothesis.”
Human beings know that some of their conscious experiences do not
refer to the real world but are only representations in their minds. Now
we can see how fundamental this step was, and we can recognize its
functional value. Not only were we able to have conscious thoughts, but
we could also experience them as thoughts, rather than hallucinating or
getting lost in a fantasy. This step allowed us to become superbly intelligent.
It let us compare our memories and goals and plans with our present
situation, and it helped us seek mental bridges from the present to a
more desirable reality.
The distinction between things that only appear to us and real, objective
facts became an element of our lived reality. (Please note that this
is probably not true of most other animals on this planet.) By consciously
experiencing some elements of our tunnel as mere images or
thoughts about the world, we became aware of the possibility of misrepresentation.
We understood that sometimes we can be wrong, since reality
is only a specific type of appearance. As evolved representational
systems, we could now represent one of the most important facts about
ourselves—namely, that we are representational systems. We were able
to grasp the notions of truth and falsity, of knowledge and illusion. As
soon as we had grasped this distinction, cultural evolution exploded, because
we became ever more intelligent by systematically increasing
knowledge and minimizing illusion.
The discovery of the appearance/reality distinction was possible because
we realized that some of the content of our conscious minds is
constructed internally and because we could introspectively apprehend
the construction process. The technical term here would be phenomenal
opacity—the opposite of transparency. Those things in the evolution
of consciousness that are old, ultrafast, and extremely reliable—such as
the qualities of sensory experience—are transparent; abstract conscious
thought is not. From an evolutionary perspective, thinking is very
new, quite unreliable (as we all know), and so slow that we can actually observe it going on in our brains. In conscious reasoning, we witness the
formation of thoughts; some processing stages are available for introspective
attention. Therefore, we know that our thoughts are not given
but made.
The inner appearance of a fully realistic world, as present in the here
and now, was an elegant way of creating a frame of reference and a reliable
anchor for all those kinds of mental activity necessary for higher
forms of intelligence. You can grasp and design possible worlds only if a
robust first-order reality is already in place. That was the fundamental
breakthrough—as well as the central function of consciousness as such.
As it turned out, the consciousness tunnel possessed obvious survival
value and was adaptive because it supplied a unified and robust frame of
reference for higher levels of reality-modeling. Nevertheless, all this is
not even half the story: We need to take one last step up the ladder, a big
one. Our brief tour d’horizon concludes with the deepest and most difficult
puzzle of all: the subjectivity of consciousness.
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