Corey J. Maley and Gualtiero Piccininiirreducible to the activity of their mechanistic components (Tononi 2008; Koch et al. 2016).
Instead of positing a function for consciousness, IIT begins with the supposition that phenom-
enal consciousness has a particular structure and proposes certain features and constraints on
physical systems that could be the physical substrate of phenomenal consciousness. According to
IIT, although consciousness itself does not (and perhaps, cannot) have a function, it may well be
a necessary byproduct of any system that processes information in the highly integrated man-
ner specified by the theory. It is the efficient processing of complex information that does the
work, rather than its byproduct, phenomenal consciousness. Therefore, what was selected for
by evolution was the efficient processing of complex information. Phenomenal consciousness
came along for free.
Analogously, some empirical approaches to the evolution of consciousness do not presup-
pose a function of consciousness. They involve identifying the cognitive or neural systems that
correlate with consciousness, identifying the species that possess those systems, and using that
information to infer when consciousness might have arisen (Mashour and Alkire 2013).
6 ConclusionPhenomenal consciousness might have evolved in one of three ways. If phenomenal consciousness
performs a function—that is, if it has physical effects that confer an adaptive advantage—it was
probably selected for. But it is difficult to establish that phenomenal consciousness has a func-
tion. In fact, many metaphysical and empirical theories of phenomenal consciousness posit that
consciousness has no function at all.
If phenomenal consciousness has no function, it might be a byproduct of some other trait
that does. For example, phenomenal consciousness might be a byproduct of a certain kind of
information integration; when that kind of information integration was selected for, phenom-
enal consciousness came along for the ride. Another possibility is that phenomenal conscious-
ness is a frozen evolutionary accident. Some adaptively neutral mutation might have caused
phenomenal consciousness to arise; later, random genetic drift might have caused phenomenal
consciousness to become fixated in the populations that had it.
There is no easy way to determine which of these explanations is correct. We need a better
understanding of the metaphysics of consciousness as well as the related question of whether
consciousness has a function. Philosophical work on the metaphysics of consciousness that
informs, and is informed by, empirical work on the evolution of consciousness is a relatively
nascent endeavor, with plenty of progress to be made. Although phenomenal consciousness and
its evolution remain mysterious, understanding the place of consciousness in our evolutionary
history may well lead to new insights into this central aspect of our mental life.^3
Notes1 Criterion (iii) may seem redundant, given that fitness—which is mentioned in criterion (i)—is often
defined in terms of reproductive success. In principle, however, a trait could spread in a reproductively
successful population due to factors other than the contribution of the trait to reproductive success.
Although this line of reasoning has been questioned (Fodor and Piattelli-Palmarini 2010), most biolo-
gists find it unproblematic: which factors directly contribute to fitness increases is an empirical question
(cf. Sober 2010).
2 In fact, etiological theories of function in philosophy attribute functions in organisms only to those
traits and features that have been selected for.
3 This material is partially based upon work supported by the National Science Foundation under grant
no. SES-1654982 to Gualtiero Piccinini.