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Evolution of consciousness: Phylogeny, ontogeny, and emergence from general anesthesia
George A. Mashoura and
Michael T. Alkireb,1
This article has been
cited by other articles in PMC.
ABSTRACT
Are animals conscious? If so, when did consciousness evolve? We address these long-standing and essential questions using a modern neuroscientific approach that draws on diverse fields such as consciousness studies, evolutionary neurobiology, animal psychology, and anesthesiology. We propose that the stepwise emergence from general anesthesia can serve as a reproducible model to study the evolution of consciousness across various species and use current data from anesthesiology to shed light on the phylogeny of consciousness. Ultimately, we conclude that the neurobiological structure of the vertebrate central nervous system is evolutionarily ancient and highly conserved across species and that the basic neurophysiologic mechanisms supporting consciousness in humans are found at the earliest points of vertebrate brain evolution. Thus, in agreement with Darwin’s insight and the recent “Cambridge Declaration on Consciousness in Non-Human Animals,” a review of modern scientific data suggests that the differences between species in terms of the ability to experience the world is one of degree and not kind.
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Evolutionary biology forms a cornerstone of the life sciences and thus the neurosciences, yet the emergence of consciousness during the timeline of evolution remains opaque. As the theory of evolution began to eclipse both religious explanations and Enlightenment doctrines regarding the singularity of human consciousness, it became clear that consciousness must have a point of emergence during evolution and that point likely occurred before
Homo sapiens. “How,” Darwin questioned, “does consciousness commence?” His post-Beagle research on this question evidently caused him violent headaches. One such headache can be expressed as the 20th century philosophical distinction of phenomenal consciousness and access consciousness (
1). Phenomenal consciousness relates solely to subjective experience, whereas access consciousness includes (among other processes) the ability to report such experiences verbally (other distinctions related to consciousness can be found in
Table 1). Thus, the scientist looking for objective indices of subjective events is primarily limited to humans manifesting access consciousness, an obstacle in studying the evolution of consciousness antecedent to our species. We could, however, take solace in the dictum that ontogeny recapitulates phylogeny and search for clues in developing humans. Unfortunately, Haeckel’s theory of recapitulation is not scientifically sound and, even if applicable in this case, we would still be constrained by the high probability that babies develop phenomenal consciousness before access consciousness. To overcome the limitations in identifying the birth of consciousness, we need a reproducible experimental model in which (
i) consciousness emerges from unconsciousness at a discrete and measurable point, (
ii) phenomenal consciousness and access consciousness are closely juxtaposed or collapsed, and (
iii) assessment of neural structure and function is possible. In this article, we consider top-down and bottom-up approaches to consciousness, nonhuman consciousness, and the emergence of consciousness from general anesthesia as a model for the evolution of subjectivity.
Table 1.
The whole paper is available at this link:
Evolution of consciousness: Phylogeny, ontogeny, and emergence from general anesthesia