What the caterpillar calls the end of the world,
The master calls a butterfly.
~ Richard Bach
The secret desire of man, since times immemorial, has been for longevity, eternal youth, everlasting beauty and immortality, which in its essence, is an aspiration for surpassing his present state of being, mired in decay, disease and death. The search for the fabled ‘elixir of life’ or for the legendary ‘fountain of youth’ has straddled several millennia and disparate civilizations alike. From the tales of Savitri,  Markandeya  and Nachiketa  in Indian mythology to the legends of Tao’s Immortals  in China who achieved physical immortality, from Hera using ambrosia to restore her defiled beauty in Homer’s Iliad to the more recent Santiago leaving his home in the search of the philosopher’s stone in Alchemist by Paulo Coelho, the dream for immortality or for a body that never ages nor withers seems to be a recurring motif in our shared cultural patrimony; a quest that is universal and eternal.
According to Sri Aurobindo, the primal, inevitable, ultimate and highest aspiration of humanity, apart from that for God, Light, Freedom, and Bliss, has been for Immortality. And this aspiration according to Him, will be fulfilled with the advent of the Supramental being on earth who will be to man what man is to the animal: beyond the Homo Sapiens, the next species.
Involution and Evolution
The manifestation of the Supramental being on earth is a logical necessity in line with the Divine plan, which can best be understood by the twin and complementary processes of Involution and Evolution. The Divine descends from His transcendent state of Sat or pure Existence through the play of Consciousness-Force (Chit) and Delight (Ananda) and with the Creative medium of Supermind, through the intermediate planes of the Overmind, Intuitive mind, Illumined mind and Higher mind into the Mind, from there into Life, finally culminating in Matter. In this process it turns into its very opposite: un-reality (the opposite of Supreme Reality or Sat), unconsciousness (the opposite of Chit) and un-delight (the opposite of Ananda). This is called the process of Creation or ‘Involution’.
When the process of involution ceases with matter, the inverse process of evolution begins. From matter to life it proceeds to reach the summit of the mind, which is at present the highest level of consciousness in earth nature. But there are other levels waiting to be manifested progressively, the next one being the Supramental consciousness. Just as the mental consciousness could not appear in an animal and required the form of man to manifest itself, similarly the supramental consciousness would need a different material sheath to embody itself. And this form will be that of the supramental being. This next species, in order to evolve out of the present man, would be aided by the “Psychic Being” and the “Supermind” itself.
The Psychic Being
The Psychic Being or the individual soul is the projection of the third divine principle of infinite Bliss, or Ananda, to aid the soul-evolution of the world. This principle comes into manifestation only at the nodus of the mind, life and body with the arrival of man on the evolutionary scene.
She puts forth a small portion of herself,
A being no bigger than the thumb of man
Into a hidden region of the heart. ||126.4|| 
Like every other cosmic principle in us, which is double, like the superficial mind and the subliminal mind, the surface vital and the true vital being, and the physical body and the subtle physical, this psychic entity in us is also double. There is the surface desire soul, which works in our vital emotions, cravings and mental seeking for power, knowledge and happiness and the true and subliminal psychic entity, “a pure power of light, love, joy and refined essence of being,” concealed by the surface desire soul.  It is when this purer psychic entity emerges to the surface that we say that someone has a soul. When one finds this essence in oneself and unites with it, one becomes aware of one’s true self and breaking through the limitation of the false ego, develops towards universality and transcendence.
When the separative ego breaks into the Superconscient upward and the Subliminal inward, it realizes its fundamental unity in the Universe in all multiplicity, and this process is called the liberation of the individual soul. It is through this process that the next evolutionary leap, in line with the Divine plan, will happen and hence “The liberation of the individual soul is therefore the keynote of the definite divine action; it is the primary divine necessity and the pivot on which all else turns.” 
Supermind: its Significance
Interestingly, Supermind is the fourth term from either side of descent (Sat, Chit, Ananda, Supermind) as well as of ascent (Body, Life, Mind, Supermind).  It is the central position of this principle that enables it to hold and link the indivisible unity of the One and the divisive distinction of the Many. It is this capacity of holding the two extremes, unity and multiplicity, which permits creation. Without the Supermind, unity could never have become a conscious, organized multiplicity and multiplicity could not have held in itself a non-disintegrating secret unity. This is basis of all creation and arrangement.
In Supermind is possible the perfect creation and arrangement because in it Knowledge, Will and Action are one; it not only Knows all truths in their inherent Oneness, but has the Will and Power to render them in creation, which alone can enable the eternal and infinite harmony of the multiplicity through its unity. Without the Supermind, the existence, consciousness and bliss of the Samam Brahman could not be developed out of their unity through Real Idea and Idea-Will. It differentiates them without dividing them, it manifests the three out of the One yet maintains them in the unity. Even when it brings forward one for a particular differentiation, it contains the other in itself either involved or explicit. It has the capacity to create “whole out of whole, and leave the whole when whole is taken away from whole.” 
Steps of Evolution: 1. Psychicisation
Once the first creation came into existence where the Supreme Being became its opposite, absolutely clueless of its origin and purpose, the Supreme Self has to enter it to rescue it, which is called as the second creation.
When all was plunged in the negating Void,
Non-Being’s night could never have been saved
If Being had not plunged into the dark… ||40.30|| 
In the Vedas this Self is described as Agni, the Divine Will, the first Avatar, who hid himself within the darkness, the immortal among mortals. It is because of this presence that the upward seeking for the Supreme in the Inconscient began. This point marks the beginning of evolution.
After millions of years of evolution, this atomic state of the universe aided by Agni, the Divine Will, has evolved through matter and life to reach the summit of the mind, which though is at present the highest level of consciousness on earth nature. It is only in the mental consciousness, which is self-aware and self-conscious that this Agni, the psychic being or the individual soul, takes the evolution forward on the “sunlit path” by becoming its leader. The realisation of the psychic being and the integration of the other three lower principles of mind, life and body around it, is the condition for the next steps of evolution: namely Universalisation and Supramentalisation.
Steps of Evolution: 2. Universalisation
The Supreme Being is simultaneously One and Many and the condition of self-realisation is the perception and the experience of the oneness in the many-ness. Says Sri Aurobindo, “The Brahman is One, not numerically but in essence. Numerical oneness would either exclude multiplicity or would be a pluralistic and divisible oneness, with the Many as its parts. That is not the unity of the Brahman, which can neither be diminished nor increased, nor divided. Unity is the eternal truth of things, diversity a play of the unity. If the One is pre-eminently real, “the other”, the Many are not unreal. Diversity is not false except when it is divorced from the sense of its true and eternal unity.” 
Self-realisation is the understanding and experiencing of the oneness everywhere. When the seeker begins to see the Lord in and surrounding all things—trees, mountains, creatures, and human beings—he sees them as images and manifestations of the same divine reality. Isha says that only this perception of oneness in the many can lead us to self-realisation. This proceeds through several steps. Initially, it is the experience of empathy, goodwill, compassion and fellow feeling for all. But, says Sri Aurobindo, “the oneness so realised is a pluralistic unity, the drawing together of similar units resulting in a collectivity, or solidarity rather than in real oneness. The Many remain to the consciousness as the real existences; the One is only their result. The real knowledge begins with the perception of essential oneness,—one Matter, one Life, one Mind, one Soul playing in many forms.”
Steps of Evolution: 3. Supramentalisation
The progressive revelation of the transcendental luminous Reality, the unity consciousness, in the multiplicity of the world, through the individual is the final aim of the universe. This luminous Emergence worshipped by the Vedic rishis is Usha, the Divine Mother, the Dynamic Truth of Illumination, who seamlessly “harmonises the dawns that shone out before and those that now must shine.” The dawn waiting to flood the world with its resplendence in this cycle of human progress is the Supramental Dawn, the Real Idea, the Creative Consciousness where knowledge, will and action are one and which sets the perfect relations between the relativities of multiple phenomenon. When we have realized our individual souls or psychic beings, organized the different parts of our being around this divine centre and realized oneness with the universe through this divine spark, we become the ready vessels to receive the golden light of the Supermind.
Supramental Being: The Glorious, Immortal Body
According to the Mother, the supramental body of the next species will be a glorious body, which will have “four main attributes: lightness, adaptability, plasticity and luminosity. When the physical body is thoroughly divinized, there will be no heaviness or tamas or unconsciousness in it. There will also be no end to its power of adaptability: in whatever condition it is placed, it will immediately be equal to the demands made upon it because its full consciousness will drive out all that inertia and incapacity which usually make Matter a drag on the Spirit. Supramental plasticity will enable it to stand the attack of every hostile force which strives to pierce it: it will present no dull resistance to the attack, but will be on the contrary so pliant as to nullify the force by giving way to it to pass off. Thus it will suffer no harmful consequences and the most deadly attacks will leave it unscathed. Lastly it will be turned into the stuff of light, each cell will radiate the supramental glory. Not only those who are developed enough to have their subtle sight open but the ordinary man too will be able to perceive this luminosity. It will be an evident fact to one and all, a permanent proof of the transformation, which will convince the most sceptical.” 
Therefore immortality as supramental beings is our luminous inevitable future that we have to work towards and the Mother and Sri Aurobindo have created the conditions required for its achievement on earth for us. Sri Aurobindo in Savitri assures us of it when he says,
In Matter shall be lit the spirit’s glow,
In body and body kindled the sacred birth;
Night shall awake to the anthem of the stars,
The days become a happy pilgrim march,
Our will a force of the Eternal’s power,
And thought the rays of a spiritual sun. ||11.47||
A few shall see what none yet understands;
God shall grow up while the wise men talk and sleep;
For man shall not know the coming till its hour
And belief shall be not till the work is done. ||11.48|| 
Sri Aurobindo’s concept of the Supramental Being as being the next species is therefore inevitable. His comprehensive framework, which aims at the immortality of the soul as well as of that of the body, explains the purpose and future of the world and all that is in it. It clarifies our position in the present hierarchy of things, and reveals to us the further vistas and the “untravelled worlds” of Tennyson that lie ahead of us and beckon us. And when we start on the adventure, we realise that there is no end to this exploration, for the “margin fades forever and forever when [we] move” like Ulysses and the closer we come to the seeming end, the further recedes the horizon for this knowledge is inexhaustible, infinite and eternal. 
In order to help us manifest this higher principle the grace of the Lord has endowed us with a semblance of its infinity and eternity, the Psychic Being, and has brought down the inexhaustibility of the Supramental consciousness closer home, thereby creating for us the conditions to grow from our current stage of “Infancy” into the “Adulthood” of Consciousness, which is to manifest this higher quaternary of Sat, Chit and Ananda into the lower mind, life and body in our lives through the medium of the Supermind; the only purpose of our existence here! 
The steps towards this great task are Psychisisation, Universalisation and Supramentalisation, the ascent into the Supermind and bringing down of this Supramental Force for the progressive transformation of mind, life and finally the body. In the words of Sri Aurobindo, “…this means the evolution not only of an untrammelled consciousness, a mind and sense not shut up in the walls of the physical ego or limited to the poor basis of knowledge given by the physical organs of sense, but a life power liberated more and more from its mortal limitations, a physical life fit for a divine inhabitant and, —in the sense not of attachment or of restriction to our present corporeal frame but an exceeding of the law of the physical body, —the conquest of death, an earthly immortality.”