Consciousness is a loosely defined or ill defined term in most instances. Here I would like to make my contribution to that confusion.
In almost all cases, when we try to define consciousness, what we inadvertently do is to think only about the human beings and their capacity for consciousness. Till date most leading philosophers and biologists have mostly failed to apply that concept to organisms other than primates at the most.
For the purpose of encompassing the experiences of all living organisms I would define consciousness as “The awareness of any organism to its surroundings”. This definition does not include the quantitative measure of consciousness and the levels of consciousness in any particular species.
What use does this definition have? By defining this way, I would like to point out the basic physiologic processes of consciousness in any species and this will in turn lead to applying the concept not only to beings with a brain but to all living organisms and cells.
I will give you a few examples to illustrate my point. Take for example a bacterium, it is a prokaryotic single celled organism which, can we consider this as capable of having any consciousness? Not if you define consciousness as a product of neurons.
Now let us consider what this individual bacterium does and how it interacts with its surroundings. A bacterium needs to feed, so it needs to correctly identify which is food and which is not, it needs to identify what is there in its’ surroundings in order to survive and replicate, so how does it achieve this?
The answer to that is in the multitude of chemical interactions that occur on the surface of the bacterial cell wall as well as inside this bacteria. Bacteria have numerous cell surface proteins and other molecules which help the bacteria in identifying different types of other molecules, including other bacteria and viruses and even many eukaryotic cells which it comes in contact with, thus leading to chnages inside this single celled organism either to gulp in the molecule, or to replicate, or to secrete toxins and so on.
Now, the bacteria is reacting to the external factors in its surroundings, even though its capacity to identify the other molecules is limited by the space and it being a single celled organism, but it still does interact with a variety of other molecules, all that is happening inside and on the cell surface of this bacterium is plain chemical interactions, it does not think as we do, but it does not need to do the complex thinking because it is a simple single celled organism, on the other hand complex, multicellular organisms need better capabilities than that because of the difference in supplying the required nutrition to the cells which are arranged in differing variations. The cells in us differentiate during embryo genesis to form particular types of cells with set functions. The work of supplying nutrition and other things are taken care by a different type of cells.
Even in multicellular organisms, each individual cell is aware of its’ surroundings through intercellular and many other types of interactions such as hormonal, neuronal interactions. They are aware of their surroundings with the help of same molecules that help the bacteria, in some cases a slightly different type of molecule with differing modes of working , this can also be called as awareness of the cell. As demonstrated in the case of cancers, where in the cells lose these particular molecules or their functions due to mutations.
Consciousness applies to single cells and it applies to multicellular organisms with brains such as humans, but the capacity varies based on the requirements.
We humans have highly evolved brains, which is a collection of neurons which have a particular function. That is cognition, memory, homeostasis, language, integration of sensory inputs and so on, this evolution has made it necessary for human beings to develop a process of thinking to survive and adapt efficiently to varying environments. This also gives us the capacity to think abstract things such as mathematics, cosmology and the very process of evolution that lead to such beings, capable of reflection and theorization.
A human being develops from two half cells which unite to become one cell and go on multiplying and differentiating to finally produce a complete organism, and throughout this process and till the time we die, all that happens in our bodies is chemical interactions and reactions to different stimuli.
Each species has a different capacity for consciousness dependent on the constitution of the body, be it unicellular or multicellular, there is no need for mystifying the concept of consciousness for all practical purposes, be it philosophical or medical.