Modern biology explains the development of life in terms of variation, selection, and adaptation, but it has yet to offer a coherent account of how or why conscious organisms evolved. It cannot say what consciousness is for, or what it does, in a way that fits cleanly within evolutionary logic. Natural selection acts on function. It explains the emergence of complex traits and structures by showing how they enhanced an organism’s chances of survival and reproduction. But consciousness, defined here not as behaviour or information processing but as subjective experience, has no clearly defined function. One can describe the adaptive advantages of perception or decision-making without invoking the felt experience of seeing red or making a choice (so this is directly related to the Hard Problem).
This leads some people to the conclusion that consciousness is an accidental, epiphenomenal by-product of brain activity, entirely lacking in causal power. But if that were the case, then it becomes unclear how evolution could have “selected” for it at all, because evolution does not select for non-functional by-products. Either consciousness has a function and influences behaviour, in which case its causal role must be identified, or it does not, in which case its evolution is inexplicable under the current paradigm. Evolution cannot select for properties that make no difference to behaviour, because natural selection operates entirely through behavioural consequences.
Further complicating the picture is the fact that we cannot observe consciousness in others directly. We infer its existence based on behaviour, but it is not at all clear why such behaviour could be, at least in principle, produced by unconscious systems. There is no empirical test to determine whether the behaviour is accompanied by conscious experience. This leads to a second major problem: we have not been able to define consciousness operationally, in terms that science can measure or model. Even if consciousness is somehow tied to brain complexity, there is no agreed-upon threshold where it is supposed to “turn on” (whatever that means), and no clear evolutionary lineage. The tools of evolutionary biology do not reveal when consciousness first appeared. There is no principled point in evolutionary history where subjective experience is supposed to appear and no empirical method for identifying such a transition.
This was Thomas Nagel's subject in Mind and Cosmos. Nagel’s central argument is that consciousness, reason, and value cannot be adequately explained by materialist or mechanistic frameworks alone. He painstakingly demonstrates why subjective consciousness cannot be merely an emergent feature of complex brains, and must somehow be a fundamental aspect of reality that demands its own form of explanation. In his view, the standard evolutionary model treats consciousness as an afterthought – something to be accommodated only once all physicalist assumptions are in place, but which fails to do justice to what consciousness is and how it appears in the world. He concludes that the only credible way to explain the evolution of consciousness naturalistically is in terms of a teleological naturalism in which mind is a basic and irreducible part of nature, not reducible to physical processes and not derivable from them through current scientific methods. In other words, he is saying that the most credible naturalistic explanation for the evolution of consciousness is that somehow it was destined to happen. He suggests this teleology must have been governed by currently unknown teleological laws, and that we should embark on a search for more examples of teleological processes in nature, so that we can develop a general theory of natural teleology. Nagel's book provoked a great deal of outrage and criticism, but personally I could not fault his arguments. The Two-phase Cosmology is a direct response to the challenge he issues at the end of it:
"I would like to extend the boundaries of what is not regarded as unthinkable, in the light of how little we really understand about the world. It would be an advance if the secular theoretical establishment, and the contemporary enlightened culture which it dominates could wean itself of [sic] the materialism and Darwinism of the gaps – to adapt one of its own pejorative tags. I have tried to show that this approach is incapable of providing an adequate account, either constitutive or historical, of our universe.
However, I am certain that my own attempt to explore alternatives is far too unimaginative. An understanding of the universe as basically prone to generate life and mind will probably require a much more radical departure from the familiar forms of naturalistic explanation than I am at present able to conceive.”
In 2PC, the evolution of consciousness is known as Psychegenesis, and it lit the fuse for the Cambrian Explosion.