Consciousness and Evolution
In the previous section, we saw that the 'Scala Naturae' was a historically used, theorized linear organization of consciousness. It served to show that the higher the order, the more complex the level of consciousness. This is only one theory to where consciousness begins to appear within animalia, and, by no coincidence, it lost much of its popularity around the same time as Darwin published "On the Order of Species."
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Darwin's writing refuted a purely linear and rigid structure to the characteristics of animals. What Darwin proposed was something much messier. Instead of a linear progression, Darwin saw branching. Multiple species developing from a singular one. He saw the characteristics of species as fluid, not static. Ever changing and dependent upon the environment. Darwin is the father of evolution, and though it took many years after his initial publication to understand the specifics of its function, evolution is now a largely accepted theory in Biology.
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The idea of evolution makes the question of consciousness a trickier one. If species development branches instead of progresses orderly, how do you identify where a certain trait developed? There are many theories that attempt to answer this question, both within neuroscience and without. In this section we will explore two theories - one in which consciousness is a trait that evolved within non-human species as well as human, and one which argues that consciousness is only an evolved trait of humans.
Consciousness in Non-Human Species
As we discussed earlier, in terms of neuroscience, consciousness is defined the state or quality of being aware of external objects as well as oneself. This definition opens up consciousness to non-human species who meet these qualifications. In order to understand where on the evolutionary timeline that this classification of consciousness would occur, we first need to understand what brain structures are necessary to bring about this acute awareness.
The mechanisms that mediate phenomenal consciousness are more easily identified and reflect the dissociation of two distinct aspects of consciousness: awareness and arousal. Awareness is the ability to perceive an object whereas arousal is the physiological response and ability to react to that object. It is believed that the frontal cortex is responsible for awareness and the midline subcortical structures are responsible mainly for arousal, but contains projections to the frontal cortex in order to relay arousal for higher level processing. Some of the evidence supporting these structures as the main areas mediating consciousness include the fact that traumatic loss of other structures (cerebellum, temporal lobe, amygdala, hippocampus) does not result in unconsciousness, however any lesioning of the frontal lobe and subcortical area results in a severely diminished ability to meet the criteria of the neuroscience definition of consciousness. Frontal cortex damage specifically affects an individuals ability to identify color and form of objects, whereas damage to the subcortical area inhibits an individuals ability to respond to stimuli and many individuals can no longer control their sleep/wake cycles. This further supports the thought that the frontal cortex is associated with awareness and the subcortical region is associated with arousal.
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More than just recognizing external objects, the neuroscience definition of consciousness also requires that the individual must possess awareness of oneself as a being. This ability to meta-analyze ones own existence is a defining factor of this type of consciousness. It is believed that the mechanism of self awareness is mediated by the limbic system, which also controls emotion. Darwin spent many of his later years trying to identify shared emotional expressions between species as he believed that if the similarities were strong enough, it would be sufficient evidence that the brain itself was more similar between species than was originally hypothesized. Darwin was correct in his assumption, and it is presently been shown that the emotional systems of many different species are extremely similar. In humans, however, the limbic system is much larger and more active. It is hypothesized by Derek Denton in ​his book "The Primordial Emotions: The dawning of consciousness" that complex human emotion evolved in response to the need to satisfy several key drives: hunger, thirst, and reproduction. The expansion of this part of our brains served to allow us to find new and creative means to meet these drives. It also allowed us to self identify. Several other species share our highly developed limbic system and self awareness. Most of these species are mammals, however a surprising few are avians. These animals include dolphins, primates, elephants, and crows.
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The idea certain brain structures may be solely responsible for the presence of consciousness in the form of both awareness and arousal indicate that the presence of these brain structures should be sufficient for consciousness. However, as with the limbic system, it seems that differences in cognitive abilities is a matter of degree and not kind. The similarities between the brains of humans and all other species is striking, however it is the subtleties(like a more complex limbic system) that allow for consciousness. That being said, this understanding of consciousness allows for non-human species to have the capacity for consciousness, and it is thought that these are the previously mentioned animals who have the ability to be self-aware.
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This extension of consciousness to certain mammals and avians has had a large impact on how we consider consciousness and has been the subject of much experimentation. It shows us that the neurobiological structures that may support consciousness are not uniquely human, which from our understanding of evolution, indicates that the development of consciousness long precedes humans on the evolutionary timescale. The presence of consciousness in diverse and somewhat sporadic species also indicates that, unlike the 'scala naturae' would assume, branching along the timescale occurred resulting in the presence of consciousness in specific subsets of species.
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The evolution of consciousness according to the neuroscience definition is a twisty and turny path, but the result is presence of consciousness within several non-human species. This allows us to view consciousness as something that developed overtime rather than as a uniquely human trait. By looking specifically at the presence of certain neurobiological structures and functions, we can get a better idea of what within the brain dictates the presence of consciousness and therefore begin to discern where temporally consciousness arose. This is something that needs to be researched more extensively in the future as the more we discover about the biological basis for this definition of consciousness, the more we will understand about the inner mechanisms of consciousness.
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Animals passing the mirror recognition test, showing they are able to identify a reflected image of themselves which is believed to indicate that they are self aware.
Midline Subcortical Area
Frontal Cortex
The Scala Naturae -
Linear organization of consciousness, static and unchanging
Fish
Amphibians
Reptiles
Birds
Simple Consciousness
Mammals
Humans
Complex Consciousness
The Modern Theory -
Reptiles
Birds
Mammals
Humans
Consciousness as an evolutionary trait that evolved somewhere on the timescale near the monophyletic branch containing reptiles and birds. Suggests that non-humans may possess more complex consciousness than initially thought. Also suggests that consciousness is not a static species trait but rather something that can evolve within a species.
Complex Consciousness
Fish
Amphibians
Simple Consciousness
Consciousness Unique to Humans
In another view of consciousness less aligned with the neuroscientific definition, consciousness is a trait unique only to humans. This view of consciousness was highly adapted by Renes Descartes, who did not deny animals ability to perceive the world around them, but held strongly to this theory that consciousness is solely attributed to humans. From his perspective, there exists a clear divide between humans and the rest of animalia, and to ascribe consciousness to any particular animal means you must ascribe it to all of animalia. All animals are living organic matter but are considered 'automata,' devoid of the higher level processing associated with consciousness.
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This viewpoint does not exactly align with the theory of spectral consciousness produced by evolution, however it does align with a potential view of consciousness in which it is an evolved trait of only humans. It draws a line on the evolutionary timeline that is closer to the present.
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Defenses of this view of evolution range from biological to spiritual. Biologically, some believe that the human brain is far advanced enough that even the most highly developed primates lack the capacity for consciousness that humans possess. Humans and other animals may have the same structures, but the evolved changes in the human brain particularly may be the only ones that allow for consciousness to exist. After all, the mirror recognition test only analyzes behavior that we deem representative of self-awareness, but we have no way of knowing for certain what the perception and association the animal has with their own reflection. Additionally, the human brain contains wiring for integration at a scale unmatched by any other species. The complex ways in which our mind can combine sensory input to form complicated, and nuanced responses is entirely unique to our species. Consciousness may be dependent upon this high capacity for integration as it allows us to form complicated languages and thoughts to analyze the world around us.
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From a viewpoint of consciousness as a spiritual entity, it would not be possible for consciousness to exist in lower order animals not containing a spirit. The terms are more or less synonymous in many interpretations, which excludes the non-human animal kingdom from experiencing consciousness though they may have the evolved brain structure that appears synonymous to humans. If consciousness is an aspect to our existence that transcends our biological features, then the point at which consciousness developed could be nowhere else but the point at which mammals split from humans.
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The view of consciousness as entirely unique to humans differs from both the scala naturae and the modern theory as it localizes consciousness only to humans. It is possible that consciousness is entirely a human trait as both biologically and from a spiritual understanding, humans may be the only possessors of the machinery necessary to meet the criteria for consciousness.
Humans
Mammals
Though there is evidence that consciousness develops spectrally over the evolutionary timeline, it is also plausible that it is a unique trait that evolves after the split between the human species and the rest of mammalia.
So what can we learn from all of this?
Though the similarity of brain structures between species suggests consciousness exists as a spectrum on an evolutionary timeline that is fluid and ever changing, it is not currently possible for us to understand the subjective experience of non-human species and thus it is impossible for us to fully understand to what degree their perception of the world aligns with our own.
This lack of understanding of animals subjective experience means that it is conversely plausible to conclude that consciousness is a unique human trait that evolved after the phylogenic split from the rest of the mammalia class.
As with all other aspects of consciousness explored so far, the position of the development of consciousness on the evolutionary timescale is again a point of contention. Is it a shared derived trait or something that separates us from the rest of animalia? Until the subjective experience of other species can be fully understood, this may be a question that goes unanswered.
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Through our investigation of consciousness from different angles, its ambiguity seems more and more daunting. As with our inability to understand lived experiences that are not our own, it seems that defining consciousness fully is dependent on many factors that lie outside our current scope of understanding. This begs the question: is consciousness something that humans can possibly fully understand given our limited view of the world?