Consciousness remains an enigmatic subject even though it has been investigated throughout human history. Many disciplines like philosophy, psychology and neuroscience study consciousness - but whether science can sufficiently explain it remains unclear. The challenge lies in the study of subjective experience; without separating mind (abstract and intangible) and body (physical and tangible).
In this blog I will motivate the idea of consciousness as an emergent property of the brain. I will cover the supporting scientific work for this idea.
Emergence is a philosophical framework used to describe properties of complex systems. A complex system forms from collective action of a number of simple entities operating in an environment. Properties of complex systems, which its sub-parts do not have on their own i.e. properties that are greater than the sum of its parts, are said to be emergent properties .
The most well known example of emergence is swarming behaviour seen in many species. It is a cooperation strategy through which individual organisms, that are limited in their behaviour, can access foraging and migratory benefits. Defensive mechanisms also emerge from swarming behaviour; swarms confuse predators that would like to pick out single individuals .
Images gallery 1: examples of (i) swarming, (ii) flocking, and (iii) schooling behaviour in animals 
The emergence framework has been used to describe evolutionary processes. Evolution is a continuous history marked by stages at which fundamentally new forms of life have appeared, including the rise of sentient animals (with nervous systems and multiple sensory abilities) and the appearance of cognitive animals . Cognitive animals are capable of cognitive functions which are the mental processes of acquiring knowledge and understanding through thought, experience, and the senses .
Higher-order consciousness in humans is thought to have emerged through evolution of the historically older trait of primary consciousness, which humans share with non-human animals. Primary consciousness includes the system’s awareness of perception and emotion . Higher-order consciousness can be described as being "conscious of being conscious" .
1.1 Previous philosophies of mind
Until the 1970s a variety of reductionist theories were prominent in the study of mind-body problem. These theories tried to explain consciousness as a sum of behavioural and physical parts. In many areas of science, reductionism has been a successful framework. However it proved limited in its explanation of consciousness. The following thought experiment explains how:
“Mary is confined to a black-and-white room, is educated through black-and-white books and through lectures relayed on black-and-white television. In this way she learns everything there is to know about the physical nature of the world. She knows all the physical facts about us and our environment, in a wide sense of ‘physical’ which includes everything in completed physics, chemistry and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including of course functional roles.
If physicalism is true, she knows all there is to know. For to suppose otherwise is to suppose that there is more to know than every physical fact, and that is just what physicalism denies.
It seems, however, that Mary does not know all there is to know. For when she is let out of the black-and-white room or given a color television, she will learn what it is like to see something red, say. This is rightly described as learning – she will not say “ho, hum”. Hence, physicalism is false” .
Consciousness is now considered a robust phenomenon wherein sensory inputs are subjectively experienced in a structured, definite, and unified way by the owner. In the following sections I will discuss the meaning of consciousness and its emergence.
2. Complexity of consciousness
Human consciousness has been described in a variety of ways by multiple disciplines . The concepts behind these multi-disciplinary definitions are summarized here:
Consciousness as experience: is the entirety of experience. This definition is qualitative, subjective and focused inward. Philosophers use the term ‘qualia’ for this definition.
Example of qualia: “When you sit on a park bench on a warm, sunny day, watching children play, the different parts of the experience—the breeze playing in your hair or the joy of hearing your toddler laugh—cannot be separated into parts without the experience ceasing to be what it is.” 
Consciousness as a waking state: is the ability to perceive, interact and communicate with the environment and with others. This definition comes from neurology. It captures the behavioural expression of consciousness. The measure of “waking state” has been objectively captured on a scale ranging from wakefulness through sleep into coma.
Consciousness as possession of any mental state: refers to the contents of mind like hopes, fears, thoughts etc. For example: “I am conscious that I may be straining your patience.” This definition is most synonymous with the mind; separated from the body.
However, the modern, most simple definition of consciousness is "sentience or awareness of internal or external existence" . This view allows for consciousness to be quite vast, and not only reserved for the upper echelons of human experience. From this perspective: any creature which is aware of its internal “Being” would be considered conscious too.
In fact, humans early in developmental stages and various nonhuman animals - including all mammals, birds and many other creatures (like bees & octopuses) are recognized as conscious . While the experience of “Being” in most animals may not be as complex as humans, clues of higher order consciousness have been found in some. Some prominent ones are described here -
Animals show self awareness as studied using the Mirror Self-recognition test. This test uses behavioural techniques to assess whether animals can recognize themselves in their reflection (mirror test).
Animals using language is also an indication, because the development of language in a species is correlated with advancement of consciousness. Well known examples include birds and aquatic mammals like dolphins & whales.
Images gallery 2: (i) gaining self-awareness is a developmental step in human children , (ii) elephants can recognize themselves in mirrors , (iii) humpback whales use language: “whale song” 
3. Neurobiological models
Pluralistic forms of consciousness, with varying complexity, exist in many animals. It appears to be a biological property bound to a physical being i.e. complex assemblies of neurons in the brain. Emergence is of interest to explain how this property is created by the brain.
This framework has seen a resurgence in the multi-disciplinary study of consciousness. Previous approaches of studying mind and body as separate systems were discarded, because the experience of “Being” could not be satisfactorily explained as a sum of its parts.
Consciousness as an emergent property of the brain is similar to emergence of higher-order traits in complex systems. Current scientific studies use this understanding. Two leading neurobiological models are briefly discussed here. These are not mutually exclusive and still being researched.
3.1 Global Neuronal Workspace
GNW is an information processing theory, which proposes that consciousness consists of a “global workspace” (shown in image 3). Global workspace has been compared to the spotlight in a theater that puts attention on the content of consciousness, while many cognitive functions work in the background. Here, the contents of consciousness refers to the information flowing between multiple cognitive systems. In this model, consciousness is thought to emerge from patterns of neural behaviour i.e. particular types of information processing.
Image 3: Schematic representation of the five main types of processors connected to the global workspace 
In this model, information input is broadcast widely through the nervous system, to recruit the operation of numerous unconscious specialized subsystems to process the data. Neurons responsible for broadcast are said to be located in the frontal or parietal lobes. Frontal and parietal lobes are major lobes of the cerebral cortex in the brain of mammals.
Consciousness happens after data is broadcast into the global workspace, leading to the subject becoming aware of it.
3.2 Integrated Information Theory
IIT proposes that the subjective experience of consciousness, the “inward feeling”, is created by causal feedback networks in the human brain. Causal feedback networks of neurons are feedback loops that reverberate with electrical activity passing back and forth. They allow the brain to understand cause and effect relationships between sensory input and action. So, the brain (system) is able to integrate current sensory processing with previously acquired memories of causal relationships to create an awareness of the world. IIT posits that such neural processes lead to emergence of primary consciousness, because the system is able to perceive its own existence.
By extension any interconnected mechanism which encodes cause-and-effect relationships will have this emergent property of existing for itself to some degree. Proponents of IIT believe that creatures with intrinsic causal power can have consciousness. They argue that Artificial Intelligence (AI) cannot synthesize consciousness by computation alone. To create consciousness, AI systems have to encode causal mechanisms.
Using clues from neurobiological experiments, the posterior cortex in the human brain has been identified as the physical origin of consciousness. This physical origin is termed the Neuronal Correlates of Consciousness (shown in image 4).
Image 4: explains physical footprint of consciousness 
4. Future perspective
So far, key questions about how consciousness relates to neural mechanisms remain unanswered. The pursuit to resolve this ‘mind-body’ problem continues. The emergent framework of consciousness creates far reaching implications beyond the scope of science into society, technology and human development. Here, I have listed a few -
If consciousness exists in non-hierarchical pluralistic states, then consciousness among animals raises ethical concerns about their treatment.
If consciousness must emerge from systems with causal feedback networks, then synthesizing consciousness merely through computation seems impossible - impacting the development of conscious AI.
If consciousness is an evolving emergent property, then the possibilities and purpose of altering human consciousness (popularly done by meditation or use of psychedelics) need to be investigated.
Finally the issue of universality of consciousness, whether consciousness among animals and humans is similar and whether consciousness is unique to individual owners or has shared properties, needs to be studied as well.
5. Watch more
I have started putting together a playlist of experts' talks and panel discussions on this and similar topics. It can be found here.
I'd like to thank Srijan Sanket and Charu Mehta for their thorough review of my writing. I have to thank Rohun Tripathi for going down many conceptual rabbit holes with me; this blog would not have happened without his company through the process.
 Jackson, Frank. "What Mary didn't know." The Journal of Philosophy 83.5 (1986): 291-295.
 Adam Zeman, Consciousness, Brain, Volume 124, Issue 7, July 2001, Pages 1263–1289, https://doi.org/10.1093/brain/124.7.1263
 Andrews, K. (2014). The Animal Mind: An Introduction to the Philosophy of Animal Cognition. Taylor & Francis. p. 51. ISBN 978-1-317-67676-8.
 Dehaene, Stanislas, Michel Kerszberg, and Jean-Pierre Changeux. "A neuronal model of a global workspace in effortful cognitive tasks." Proceedings of the national Academy of Sciences 95.24 (1998): 14529-14534; DOI: 10.1073/pnas.95.24.14529