Your right to do what is just and right and not what was destined, is the definition of Dharma directly dictated to me by God Almighty, Brahman a few days after I realized self, realized god in the wee hours of third of August 1993 at 37 years of age. This definition of dharma just cannot go wrong. It also indicates that Dharma instinctively, inherently exists within all living beings including human beings from the beginning.
Even before a single religion came into existence on mother earth Dharma still existed. It is based on Dharma human beings conducted affairs of life amongst themselves.
The explanation of Dharma is best rendered in Bhagavad Gita and Upanishads (independent spiritual treatises).
Initially manifest tree of Dharma (righteousness). This tree grew but had four compartments. When the brain of human beings evolved accomplished sages and Rishis came into scene. These Sages and Rishis finally invoked first words of God Vedas (Hinduism revelations) directly from God, Brahman. The Vedas are four in numbers, Rig Veda, Sama Veda, Yajur Veda and Atharva Veda. With the manifestation of Vedas the inner stem of tree revealed itself.
But the four Vedas were very voluminous, difficult even for scholars to decipher. The tree of Dharma grew further and manifested Lord Krishna, the first avatar to manifest on mother earth. And with Lord Krishna came sermon of Bhagavad Gita. The essence of all four Vedas relating to spirituality is contained in 700 shlokas verses of Bhagavad Gita.
For mankind at large the contents of Bhagavad Gita were easier to decipher. Spirituality finally spread its roots to masses, commoners. The message of Bhagavad Gita was not only easier to understand but also to preach.
The tree of Dharma grew further and developed its first branch and manifest Mahavira, 24th Tirthankara of Jainism, preceptor. About 77 years later the tree of Dharma grew another branch and Siddhartha Gautama manifest on the scene. About 423 years later another branch and advent Jesus Christ! A few centuries later another branch and arrived Prophet Mohammed.
The tree of Dharma is still growing with all its branches. Dharma is the sap of life. In absence of Dharma humanity, mankind just could not exist. All would behave like animals.
The precept of Dharma even in present times is not only valid but the only cause that sustains life.