Corey J. Maley and Gualtiero PiccininiAll of these theories have merits, and different aspects of them seem to accord well with our
introspective experience. If they are correct, the functions they assign to phenomenal conscious-
ness may be what consciousness was selected for. Each theory also faces the problem that many
cognitive states and processes, which involve carrying and processing information, occur entirely
unconsciously. It is not clear why the specific states or processes identified by these theories
should require phenomenal consciousness.
On the other hand, simply because a function could be realized in a non-conscious system,
that does not mean that the conscious system in question does not, in fact, have that function.
For example, consider the Krebs cycle. In aerobic organisms, the Krebs cycle is a series of bio-
chemical reactions that uses (among other things) oxygen to produce ATP, which is used by
cells as a source of energy, and carbon dioxide, which is a waste product. It is also possible to
produce energy without the Krebs cycle; for example, anaerobic organisms cannot use the Krebs
cycle because it requires oxygen. It would be wrong to say that the Krebs cycle lacks the func-
tion to produce energy, just because some other mechanism also produces energy in a different
way. In the case of consciousness, then, the mere fact that some other mechanism could perform
whatever putative function one thinks consciousness has does not prove that consciousness lacks
that function.
Still, there is an important point that follows from these considerations. While it is true that
the Krebs cycle has the function of producing energy in aerobic organisms, it could have been
some other mechanism. The fact that it is the Krebs cycle, and not some other mechanism, is a
contingent fact of evolutionary history. Similarly, if consciousness has a function that some other
mechanism could perform, then it might also be a contingent fact of evolutionary history that
we have consciousness. Had evolutionary history been different, we might have had a mental life
in which we are not conscious, yet our mental life would otherwise be identical.
From the point of view of evolution by natural selection, the possibility that we could have
evolved without phenomenal consciousness—that is, that we could have evolved to be zom-
bies—is not surprising: many traits are a matter of contingent historical happenings. But from
the point of view of our mental life, this is quite surprising. If anything seems to be the core
of who we are, of what it is to be human, and what makes life worth living, it is phenomenal
consciousness. That consciousness is just another contingent trait is in tension with the idea that
being conscious is essential to being human.
In summary, adaptationism about consciousness presupposes that consciousness has a func-
tion, but all of the extant theories that propose a function for consciousness face the same
challenge: it seems possible that the proposed functions could also occur in a non-conscious
system. If that is the case, the proposed functions might be functions of non-conscious systems
that merely correlate with phenomenal consciousness, without being functions of phenomenal
consciousness itself. If so, consciousness itself cannot be an adaptation. This leads us to theories
that do not propose a function for consciousness. The theories that propose that consciousness
does exist, yet has no function, are incompatible with adaptationism about consciousness. They
are compatible with the view that consciousness is either a byproduct of other traits or an evo-
lutionary accident.
5 Consciousness as a Byproduct or Evolutionary AccidentPhenomenal consciousness may have no function, and thus may have no adaptive value what-
soever. However, it may still be possible to explain consciousness using the resources of evolu-
tionary biology; we simply have to look beyond natural selection. In particular, if phenomenal
consciousness has no adaptive value, then it may be a byproduct of some other biological trait