Corey J. Maley and Gualtiero Piccininithe distribution of blood types is relatively fixed. In smaller populations, however, traits can end
up dominating others merely because of chance, and become fixated.
Providing an evolutionary explanation of a psychological trait is especially challenging for
two additional reasons. First, psychological traits leave few if any traces in the fossil record, so it is
difficult to identify the psychological traits of ancestral organisms. Second, typical psychological
traits are the result of a complex interplay between innate and environmental factors, making
it difficult to identify variations in psychological traits that are genetically heritable and hence
subject to evolutionary effects. Both of these challenges apply to phenomenal consciousness.
Finding a place for phenomenal consciousness within evolutionary history faces two addi-
tional challenges: there is little consensus on what the physical basis of consciousness is, and
there is no consensus on how phenomenal consciousness relates to its physical basis. On the
latter question, there are two relevant options. Option one is that phenomenal consciousness is
produced by its physical basis but has no physical effects of its own. This view is known as epi-
phenomenalism; many metaphysical views about phenomenal consciousness are committed to it.
Option two is the opposite of option one: phenomenal consciousness has physical effects of its
own. If option two is correct, a further question is whether the physical effects of phenomenal
consciousness confer adaptive advantages—i.e., they perform at least one function. If they do
perform functions, a final question is whether phenomenal consciousness is indispensable to
fulfilling its functions or its functions can also be fulfilled by non-conscious systems.
4 Consciousness as AdaptationMany mental faculties and capacities have obvious functions. For example, perceptual sys-
tems have the function of acquiring usable information about the environment, and motor
control systems are for initiating purposeful behavior. Mental faculties and capacities with
clear functions are likely to have been selected for by evolution because of the advantages
conferred on organisms by the functions they perform.^2 By contrast, it is especially difficult
to see how phenomenal consciousness could have a function, and thus how it could have
been selected for.
Nevertheless, various functions of phenomenal consciousness have been proposed, such as
allowing organisms to construct an internal model of the world, perform certain inferences,
learn in certain ways, perform voluntary actions, or represent themselves. If any of these adapta-
tionist hypotheses is correct, it is likely that these functions are what phenomenal consciousness
was selected for, and that would be the basis for the evolutionary explanation of consciousness.
According to adaptationism about phenomenal consciousness, when phenomenal conscious-
ness arose during evolutionary history, it conferred an adaptive advantage to organisms that had
it; because of this adaptive advantage, phenomenal consciousness was selected for (Barron and
Klein 2016; Feinberg and Mallatt 2013; Ginsburg and Jablonka 2010; Grinde 2013).
If phenomenal consciousness has a function, one follow-up question is whether phenomenal
consciousness is nomologically necessary to perform that function. If so, then that function
cannot be performed by any non-conscious system: the only way that evolution can gener-
ate organisms that perform that function is to select for phenomenally conscious organisms.
Establishing that phenomenal consciousness is nomologically necessary to perform a function
is hard: it would require determining the physical nature of phenomenal consciousness and
establishing that such a nature is required to perform the function of consciousness. But there
is no consensus on the physical nature of phenomenal consciousness—or on its function, for
that matter. Therefore, the nomological necessity of phenomenal consciousness for its function
is unlikely to be established any time soon.