Whether we born into any living beings depends on our Karma hidden in the Life itself and it depends in the Life-condition of being we bring.
One of the prime concerns of Buddhism is our life-state, a condition which, at any given moment, can range from joy to suffering. One's life-state is always seen as an interaction between external conditions and inner tendencies; the same conditions (the same workplace, for example) experienced by one person as unremitting misery may be a source of exhilarating challenge and satisfaction to another. Strengthening our inner state of life so that we are able to resist and even transform the most difficult and negative conditions into something positive is the purpose of Buddhist practice.
Based on his reading of the Lotus Sutra, the sixth-century Chinese Buddhist scholar, T'ien-t'ai, classified human experience into ten states or "worlds." Nichiren adopted and elaborated upon the teaching of the Ten Worlds, by emphasizing the inner, subjective nature of each world: "As to the question of where exactly Hell and the Buddha exist, one sutra reads that Hell exists underground and another sutra says that the Buddha is in the west. However, closer examination reveals that both exist in our five-foot body." (Major Writings of Nichiren Daishonin, Vol. 1, page 271.)
What then are the Ten Worlds? Ordered from the least to the most desirable, they are: Hell--a condition of despair in which one is completely overwhelmed by suffering; Hunger--a deluded state dominated by desires that can never be satisfied; Animality--an instinctual state of fearing the strong and bullying the weak; Anger--a state characterized by an unrestrained competitive urge or ego to surpass and dominate others, often with a pretense of being good and wise. These four states are referred to as the "Four Evil Paths" because of the negative, harmful results of actions based on these life-states.
Continuing, Humanity is a tranquil state marked by an ability to reason and make calm judgments. While fundamental to our identity as humans, this state is a fragile one that can yield to one of the lower states when confronted with negative conditions. Rapture is a state of joy typically experienced when desire is fulfilled or suffering escaped, and is also vulnerable to external conditions. The worlds thus far are sometimes grouped together as the "Six Lower Worlds." These states are all essentially reactions to changing external conditions in which we experience a lack of real freedom and autonomy.
What Buddhism refers to as the "Four Noble States" represent the effort to live with integrity, inner freedom and compassion. The world of Learning describes a condition of aspiration for self-improvement and enlightenment. Realization indicates a state in which one has insight into the true nature of phenomena. Together, these are sometimes referred to as the "Two Vehicles"; those manifesting these states are partially enlightened and free from some deluded desires. But these worlds can be very self-absorbed. In many Buddhist texts we find the Buddha admonishing the people of the Two Vehicles for their arrogance, selfishness and complacency.
The world of Bodhisattva is a state full of compassion in which we overcome the selfish ego and work tirelessly for the welfare of others. Mahayana Buddhism in particular sees the Bodhisattva state as ideal human behavior. Buddhahood is a state of boundless wisdom, compassion and freedom, in which one is able to savor a sense of unity with the fundamental life-force of the cosmos. For someone in the state of Buddhahood, everything--including the inevitable trials of illness, aging and death--can be experienced as an opportunity for joy and fulfillment. The inner life-state of Buddhahood makes itself visible through altruistic commitment and actions enacted in the world of Bodhisattva.
This brings us to a key aspect of Nichiren's understanding of the Ten Worlds: Each world contains within it the other nine. As he expresses it: "Even a heartless villain loves his wife and children. He too has a portion of the Bodhisattva world within him." (Major Writings of Nichiren Daishonin, Vol. I. pp. 53.) Thus, the potential for enlightened wisdom and action represented by the world of Buddhahood continues to exist even within a person whose life is dominated by the lower life-states of Hell, Hunger or Animality.
The reverse is also true. The life-state of Buddhahood is not separate or discontinuous from the other nine worlds. Rather, the wisdom, vitality and courage of Buddhahood can infuse and transform the manner in which a tendency toward, for example, Anger, functions in a person's life. When Anger is directed by the compassion of the worlds of Buddhahood and Bodhisattva, it can be a vital force in challenging injustice and transforming human society.
The purpose of Buddhist practice--for Nichiren Buddhists this includes the recitation of the mantra Nam-myoho-renge-kyo--is to bring forth the life-state of Buddhahood which can illuminate our lives and the lives of others and enable us to generate lasting value as we live out our lives in the Ten Worlds.