The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago

Abstract

Vertebrates evolved in the Cambrian Period before 520 million years ago, but we do not know when or how consciousness arose in the history of the vertebrate brain. Here we propose multiple levels of isomorphic or somatotopic neural representations as an objective marker for sensory consciousness. All extant vertebrates have these, so we deduce that consciousness extends back to the group's origin. The first conscious sense may have been vision. Then vision, coupled with additional sensory systems derived from ectodermal placodes and neural crest, transformed primitive reflexive systems into image forming brains that map and perceive the external world and the body's interior. We posit that the minimum requirement for sensory consciousness and qualia is a brain including a forebrain (but not necessarily a developed cerebral cortex/pallium), midbrain, and hindbrain. This brain must also have (1) hierarchical systems of intercommunicating, isomorphically organized, processing nuclei that extensively integrate the different senses into representations that emerge in upper levels of the neural hierarchy; and (2) a widespread reticular formation that integrates the sensory inputs and contributes to attention, awareness, and neural synchronization. We propose a two-step evolutionary history, in which the optic tectum was the original center of multi-sensory conscious perception (as in fish and amphibians: step 1), followed by a gradual shift of this center to the dorsal pallium or its cerebral cortex (in mammals, reptiles, birds: step 2). We address objections to the hypothesis and call for more studies of fish and amphibians. In our view, the lamprey has all the neural requisites and is likely the simplest extant vertebrate with sensory consciousness and qualia. Genes that pattern the proposed elements of consciousness (isomorphism, neural crest, placodes) have been identified in all vertebrates. Thus, consciousness is in the genes, some of which are already known.

Synthetic consciousness: the distributed adaptive control perspective

“…A detailed analysis of both the vertebrate and invertebrate nervous system has led to the suggestion that the central complex in the insect brain serves the same functions as the CBS and thus provides an anatomical signature for invertebrate consciousness ( [97], but see [98] for an alternative interpretation of this structure). An associated proposal advances the hypothesis that primary consciousness and the CBS evolved in two stages about 520 Ma ago, driven by the emergence of distal sensing afforded by vision and the required need for the realization of map-like representations [99]. This, in turn, further accelerated vertebrate evolution by allowing the exploitation of more complex niches.…”

What insects can tell us about the origins of consciousness

“…As noted above, the key structural elements of the vertebrate behavioral core control system are all present and functional in lampreys (128). If these structures are present in the basal vertebrates then they may also have been present in the basal vertebrate species Haikouichthys identified in Cambrian fossil fauna (128). This species had welldeveloped eyes and a hydrodynamic eel-like body (129).…”

“…This species had welldeveloped eyes and a hydrodynamic eel-like body (129). It is reconstructed as an active swimmer (129) and presumably had a version of an operational behavioral core control system for the organization of dynamic and active movement, action selection, and target selection (128).…”

On the evolution of conscious attention

“…Surprisingly, little focus has been given to the evolution of attention (but see Cosmides & Tooby, 2013;Tooby & Cosmides, 1995;Ward, 2013;Wright & Ward, 2008, pp. 235-241), especially in terms of how it relates to the evolution of consciousness, which has received more treatment in the literature (e.g., Feinberg & Mallatt, 2013;Nichols & Grantham, 2000;Polger & Flanagan, 2002;.…”