I have taken the liberty to synthesise a correlation based on the wisdom of upanishads and modern psychology, explaining evolution and existence. From Taittirīya upanishad, I refer to the doctrine of five sheaths (koshas). I have also used the classification of brain and mind according to modern psychology. In order to understand the large picture, we must be aware of each of the constituents of the consciousness.

Brain & its Classification: 

Brain is an internal organ responsible for computation of sensory inputs, which also serves as the cradle of consciousness and as a nursery of imagination and thoughts. As an internal organ it has an objective reality, and as substratum for thoughts, imagination and consciousness it has subjective reality. Reality and creativity fuses here. Based on its evolution, scientists have classified it in three stages:

1. The OldBrain - First in the line of evolution, so it is old. shared by other members of the animal kingdom, often referred to as the reptilian brain. It is dedicated to the cause of the Essential Triad. It is the strongest and constitutes a large portion of the physical brain. When you dodge a ball while playing, or feel an inexplicable attraction to a potential mate, or when you can’t ignore the scent of a delicious food - you can feel your old brain at work. It is wired for survival. It restlessly scans the environment, controlling impulses, motor and other internal organs. It also serves inputs to other parts of the brain. It is the storehouse of consciousness. 
2. The MidBrain - Next in the line of evolution. It houses the emotions. Emotions play a vital role in humans. Even some other animals like cats, dogs, monkeys show emotional reflexes, but they are not as developed as in humans. Emotions may or may not have rational explanations. It may be a response to sensory inputs or creative impulses from the new brain. In any case, it serves as the basis of most of our voluntary actions.
3. The NewBrain: Last in the line of evolution, yet the most powerful. As sole owner of reason, it has infinite possibilities. Here consciousness becomes a value, when it gives way to awareness. Thoughts, expressions and voluntary actions come under the functional domain of the NewBrain. Morality as an outcome of reason is facilitated by this faculty of brain. With creative capabilities, it marks the territory of humans. Arts and sciences, philosophy and religion, poetry and painting with the miracles of learning which constitutes the subjective reality becomes possible. 

Mind & its classifications:

Like a computer with no operating system is useless, so is a brain without mind. Brain is lifeless and inert on its own, as a part of the body it is prone to death. The light of the soul on our existence, reflects as the mind. Consciousness is realised through the mind. It is not as concrete as the physical brain, as no physical existence can be ascribed to it. All we have is a brain and we conceptualise a mind to explain thoughts and imagination. Mind is the rational component of the abstract existence of humans. Mind can be assumed to be analogous to awareness, but usually has a wider dominance. When awareness and mind overlaps this dominance, liberation becomes possible. Based on the level of awareness, mind is broadly classified as - 

1. Unconscious Mind: That part of mind where awareness is yet to penetrate falls under the unconscious domain. It is the vast reservoir of the unknown that man fears the most. It can be equated with reference to the OldBrain, the always active part of the brain.
2. Subconscious Mind: As part of infinity, awareness can catch glimpses of this possibility. It is the repository of infinite wisdom. It can be ascribed to the Midbrain. Unpredictable and beyond the reign of reason. 
3. Conscious Mind: Adjacent to the new brain, the awareness envelops its dominion. Voluntary actions, thoughts and imagination fall under this category. Reason dominates consciousness, which as a fragment is present here. Consciousness and conscious mind are mistakenly considered as one and the same thing. Only self-consciousness is possible with conscious-mind.

Doctrine of five sheaths

This doctrine explains the evolution process, which bears close resemblance to the scientific explanation of evolution from single celled organisms to the complex creatures like humans. It marks five stages of evolution.

1. Annamaya: the Physical plane - The lowest level is that of matter, which is unconscious and dead and cannot account for life. The purpose of matter is fulfilled only when life is evolved. This highest state of matter is therefore life. Though, matter cannot account for life, there can be no life without matter.
2. Prānamaya: the Biological plane - The vegetable life emerges here. Life pervades the universe and binds man with the rest of the creation on this plane of existence. 
3. Manomaya: the Mental or Psychological plane - This state is shared by lower animals with men. Mind and consciousness remain in lower animals at the level of instincts and reflex actions. The subject object duality is absent here, as it has not yet evolved. Actions are not subjective or voluntary. There is a scope of involuntary actions alone. 
4. Vijñānamaya: the Metaphysical plane - The stage of evolution of conscious reason. This state is the sole monopoly of human beings. Reason becomes self-conscious only at this stage  and this fact distinguishes human beings from other lower animals. Arts, sciences, aesthetics, morals, poetry, philosophy, religion, all become possible only at this state. The empirical trinity of knower, knowledge and known evolves. Ego gains prominence here. 
5. Ānandamaya: the Mystic plane - The abode of bliss with no trace of duality or plurality. Objective and subjective reality become one. The empirical trinity of knower, knowledge and known fuses into a transcendental unity. Reason terminates here. The plane that is responsible for spiritual and religious pursuit of mankind.

It must be noted in this context, that the doctrine does not prescribe that the lower is lost in the process, it is simply transformed into the higher. Matter is not lost in life; life is not lost in mind; mind is not lost in reason; reason is not lost in bliss. Brahman or the ultimate Existence pervades them all. 

The synthesis

I have tried to simplify the concept in a diagram below, backed up by an explanation. It closely resembles the metaphysical postulations given by Aurobindo, using the concept of evolution and involution. Though I have tried to give it a unique interpretation leveraging some concepts of psychology. Anyways, I hope that this effort will help you in determining the value of your existence. This is the core premise on which the philosophy of Lifeconomics is based. So, give it some time to sink in your intellect. This is more a theoretical explanation so may get confusing. Don’t worry if I fail to bring enough clarity as of now. In the prospective practical implementation, I hope the concept will clarify itself.

At the lowest level i.e. on the Physical plane, Annamaya - we have nothing but lifeless matter. Life can be envisioned only in its contradictions. Thus, the possibility of a body can be conceptualised. This plane is governed by space and time in a dictatorial fashion. Here ignorance dominates, with absolute darkness. Senses and intellect are non functional. So, the possibility of other matters or any motion is beyond cognizance. Even if anything is present, it is unknown. Life in any form is non-existent. 

Then, to meet the needs of evolution, ‘life’ comes into existence on the Biological plane, Pranamaya. Motion begins. Matter becomes valuable with the advent of life. Maybe single-celled organisms evolve. Along with it the OldBrain with an unconscious mind, dedicated to the cause of survival, revolting against the tyranny of ignorance comes to the light of life. Ignorance is challenged by consciousness. Throughout the evolutionary process the OldBrain and unconscious mind will continue to support life, resisting against the authority of space and time. Together they will ensure progress for life. Interaction between matter and life begins. Senses develop, but intellect is still in its infancy. Reflexes become an objective reality with no traces of subjective responses. 

Beyond the dominion of space and time, subconsciousness establishes a territory. Emotions gain its prominence at the Mental plane, Manomaya. Still the matter is objective, with no division. Reflexes yield instincts that grant life immense values. Instincts can hardly be categorised as subjective, it is more like reflexes to stimulus. Yet, hints of subjectivity can be traced to instincts. Even involuntary reflexes have a tinge of subjectivity as the substratum of such reflexes. The subjective side of OldBrain lays the bedrock for further evolution. Senses grow stronger. Consciousness develops further to embark life with awareness. MidBrain with a subconscious mind builds a foundation for reason in the form of emotions. 

When emotion matures, reason makes an entry on the Metaphysical plane, Vijñamaya. Emotion is the mother of reason, where life plays the role of father. Reason launches a mission to question each and everything. The NewBrain unfolds a conscious mind, self-aware of its presence. Awareness that was yet unaware of its own being, asserts independence with the newly found superpower of self-awareness. The awe and wow of life helps the intellect gain intelligence. Reason equipped with intelligence, becomes restless to seek answers establishing academic disciplines. Life now vibrates with its full potential in manhood. Subject, the knower identifies the object, as known in form of the knowledge. This process sets up a province where ego declares its dominance. The Concepts of ‘I’ and ‘mine’ create individual worlds within the scope of the universe - infinite microcosms in the unified grand cosmos. Thus, reigned by diversity the existence prospers. 

So far, existence somehow manages to overcome the constraints of space with the help of reason. Academic progress, research and technology gains a command over space. But time poses a greater challenge than before. Life curtailed by death in time provokes reason every moment. When the energy of reason exhausts, it seeks rest in peace and bliss on the mystic planes, Ānandamaya. Is it a figment of imagination or a reality, reason can never be certain. Bound by restraint of space and time it conceptualises the probability infinity and eternity as logical necessities. In search of liberation from the hustle and pain of life, life imagines for itself such possibility. The knower drops the weapon of knowledge forged by reason from elements of the known, in absolute surrender. The infinity of microcosm again unifies to the might of the cosmos. Thus, completing the process of evolution. Destiny can be delayed by adding layers to evolution but can’t be entirely eliminated.

Body and consciousness would have been sufficient to explain the existence, if they were not limited by death. But death mandates a reasonable explanation for after-life. That’s where the concept of soul steps in, as the master of infinity and eternity, the point where the trinity of knower, known and knowledge fuses in unity.