The Biological Evolution of Consciousnessthat itself was selected for—what Gould and Lewontin (1979) called a spandrel. Alternatively,
consciousness may simply be an evolutionary accident. Either way, while consciousness itself
has no function, it is intimately related to something else that does. We have referred to the
view that consciousness is either a byproduct or an accident of evolution as the Byproduct or
Accident View, i.e., BAV (Robinson, Maley, and Piccinini 2015). On this view, consciousness is
not explained by appealing to its function. BAV takes consciousness to be similar to many other
biological traits that are not explained via their direct adaptive value.
To begin with, let’s consider the possibility that consciousness is a byproduct of some other trait.
It may be that consciousness occurs when neural tissue of enough complexity is actively processing
information in a certain spatiotemporal region. Consciousness itself does not do anything. Or, if it
does do something, what it does has no adaptive value. In addition, consciousness is not identical to
the neural activity that gives rise to it. Although neural activity does have many functions, it simply
happens that consciousness is a byproduct of that kind of neural activity.
Consider a psychological process, such as human facial recognition, that (presumably) has
been selected for. This capacity relies on neural structures that process complex informa-
tion. These neural structures do many other things as well, such as generate small electrical
fields (which is what EEGs are able to detect), produce small amounts of heat, and so on. Of
the many things that these particular neural structures do, the ability to recognize faces was
selected for, whereas producing electrical fields and heat were not. It just so happens that a
certain amount of neural tissue functioning in a compact space generates electrical fields and
heat. Consciousness may well be like that: it is simply a byproduct of neural systems function-
ing in a certain way.
If consciousness is a byproduct of some other trait, a further question is whether it is a
contingent or necessary byproduct. It is a contingent byproduct if one of the following is the
case: either there are organisms that function just as well as conscious ones but without con-
sciousness, or there could have been such organisms had evolution proceeded differently. This is
analogous to the transparency of insect wings. Again, many insect wings are transparent, but this
is a contingent byproduct of what they are made of: add pigment during development and the
wings cease to be transparent. By contrast, consciousness is a necessary byproduct if, as a matter
of natural law, any physical process that performs certain cognitive functions gives rise to con-
sciousness—even though the physical processes themselves are unconscious and consciousness
has no functions of its own.
The other option is that consciousness is a frozen evolutionary accident. It may be that all
cognitive functions can be performed entirely unconsciously, without giving rise to any con-
scious state or process. Yet, at some time during evolution, some harmless mutation arose that
causes phenomenal consciousness to occur under certain circumstances—e.g., when certain
cognitive functions are performed. If this mutation were lost, we would lose all phenomenal
consciousness but keep on functioning exactly as before—just without consciousness. We’d
become zombies. But this mutation became fixated through random genetic drift. Since it’s
harmless, it sticks around. This is analogous to the proportion of blood types within the human
population. As far as we know, humans could do with only a single blood type, and no blood
type appears to confer any advantage over any other. At the same time, no blood type appears to
create any disadvantages either. Thus, the proportion of different blood types is an evolutionary
accident.
There are theories of consciousness—the most prominent among them Information
Integration Theory (IIT)—that attempt to explain consciousness without appealing to any
supposed function of consciousness whatsoever. According to IIT, consciousness is an emer-
gent property of certain systems that are capable of processing information in complex ways,