Consciousness 2: Evolution and consciousness. (Evolutionary perspective) (v1.0)

 Most of this material is from the National Institute of Health web site. 

Are animals conscious? If so, when did consciousness evolve? 

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. It has become clear that consciousness must have a point of emergence during evolution and that point likely occurred before Homo sapiens. There are many dimensions to a study of consciousness (like evolutionary perspective, neurological perspective, philosophical perspective, and psychological perspective). Here I will focus on only evolutionary aspects. The views here are not harmonized with views from other dimensions. 

Phenomenal consciousness is subjective experience itself, whereas access consciousness is that which is available to other cognitive processes (such as working memory or verbal report). Thus, the scientist looking for objective indices of subjective events is primarily limited to humans manifesting access consciousness, a big obstacle in studying the evolution of consciousness antecedent to our species. Babies develop phenomenal consciousness before access consciousness. 

Early morphologic examination of brain differences across species suggested the capacities of consciousness increased as brains evolved from more primitive reptilian organization to mammalian (or, with a limbic system, paleomammalian), and then neo-mammalian organization, characterized by an intricately folded neocortex. But this view now is largely considered to be false. Newer findings strongly refute this model of a brain, especially the concept of a later developing neocortex. 

The basic behavior of an organism is driven by a fundamental physiologic need to maintain homeostasis (A state of balance among all the body systems needed for the body to survive and function correctly). Creatures that could meet their basic homeostatic needs are the ones that survived; those that did not suffered extinction. The basic behaviors driving homeostasis are evident as far back as the first multicellular organisms that needed a vascular system to provide nutrients to those cells no longer exposed directly to the environment. This is a major evolutionary force. 

In 2005, Denton posits that the most basic instincts, such as thirst, hunger for air, hunger for salt and food, and the desire for sex are the defining starting points for evolving a conscious brain. This idea holds within it the concept of intention, desire, and action selection, where the basic intention of a movement is in the service of fulfilling a desire. Consciousness may not have emerged from the need to make an internal representation of the outside world, but rather as an extension of very basic primitive or primordial emotional influences. Such emotional influences would generate a response in an organism and prepare its brain for action. 

The brain structures needed for generating arousal (look up arousal theory of motivation) and primitive emotional responses are generally located in the brainstem, midbrain, and limbic system and are as old as the vertebrate radiation itself. A study of Lampreys indicates they are capable of making an action choice depending on the situation with which they are confronted. The “reduction of uncertainty” through action selection may be the precursor to the highly informative states of consciousness. More complex neocortical abilities offered a survival advantage to more complex brains by giving organisms a larger grasp of their surroundings, but these systems developed over time and used sensory information from the environment. This coupling of an internally based need system with an externally based situational awareness system is likely the foundation for the emergence of consciousness. 

Earlier, some thinkers expressed serious concerns about attributing higher levels of consciousness to all life. Indeed, René Descartes, often considered the philosophical father of the mind–body relationship, questioned whether a conscious self, arose in the animal kingdom. This all-or-none approach did not reflect an evolutionary theory perspective, which raised the possibility of a conscious continuum in discussing the emergence of consciousness in animals.

The Cambridge declaration of consciousness in non-human animals in 2012 puts forward the hypothesis that the capacity for consciousness likely emerged very early in evolutionary terms, and those processes that support consciousness in humans are likely characteristic of many living creatures. In fact, according to the declaration, based on a number of considerations from comparative brain anatomy and current knowledge about the neurobiology of consciousness, it would seem almost certain that at least some form of consciousness is present in all mammals and could have emerged on the evolutionary timeline at the branch point of amniotes (vertebrate animals like a mammal, bird or reptile).

One key component of consciousness that seems linked to higher cognitive abilities is awareness of the self rather than simply awareness of the environment. A somewhat objective but not perfect test of this is the mirror response test - how animals react to their own image in a mirror (Mirror self-recognition test - MSR - however not everyone agrees this is a good test). Animals that have passed the MSR test to various degrees include Chimpanzees, Bonobos, Orangutans, Gorillas, Asian Elephants, Eurasian Magpies, Cleaner Wrasse (a fish) and bottlenose Dolphins. In some animals the test is more definitive than others and it is more definitive among primates. The distinction among primates suggests that the qualitative nature of the conscious experience varies greatly across species. The introspective reflective nature of human consciousness may be evolutionarily quite rare and may be unique. In evolutionary terms, if objective evidence of self-awareness can be taken as evidence for consciousness, then consciousness as it occurs in the primate with their more fully developed cortex may have evolved ~5 million years ago, at around the time when great apes split off from the lesser apes.