Hinduism does not preach castes by birth and that it is very much possible for a Shudra to become a Brahmin in the same life, I requested him to furnish documentary evidence. It is also important to note that NO varna is considered superior; they are all equal. No "high caste," no "low caste." I furnish this to all of the experts of Hinduism in India to rebut if they can. If not, the hereditary caste system should be declared illegal, violative of the roots of Hinduism, and abolished by Hindu leaders. At once. Let merit prevail. Let competent "shudras" become Brahmins and let incompetent and corrupt Brahmins become Shudras (if at all such names are needed to be used).
     This is an open challenge to anyone who claims to be Hindu anywhere in the world. [am I stirring a hornet's nest?] No. This is a seriously discriminatory thing - casteism - which must be destroyed completely. No modern society can allow such a thing and call itself civilized. When monarchy has been abolished in the Indian republic, hereditary caste system must go. Why is this issue relevant? In the context of the call for leaders of Hinduism to abolish the caste system. All religions must modernize and not only claim equality of all humans before God, but demonstrate it by their actions and laws. Regarding 4 Varnas - Brahmin, Kshatriya (Rajanya -vedic term), Vaish and Shudra ‘by birth,’ there is no mention in the Vedas. Rig Veda 10-92, 10 to 12, Atharva Veda 19-6, 6, Yajurveda 31-11, 13 & 17, Brihadenyaka Upinashad 1-4, 11 to 14 mention as below (summary): "In the beginning, there were only unskilled workers, society did not flourish. Then came traders and agriculturists but society still did not flourish. Society finally began to flourish when rulers (kings / elected presidents), bureaucrats, Armed Forces became a part of society. Thus came the 4 Varnas of Divine Origin. In this society, a Father could be an unskilled worker, whereas children could be traders, bureaucrats, soldiers or preceptors."
     So long as these 4 groups based on divine professions follow Dharma (righteousness) & Rta (cosmic laws of social, moral and political order), they remain part of 4 Varnas otherwise, they become Avarnas, Vritas (Rta defaulters) and Kimidin (evil minded persons, bribe takers etc). Atharva Veda 3-21-5, Sama Veda 179, 913 - Hydra-headed corruption (of 9 kinds) from 99 sources enter the body & make them follow ignoble and non-divine activities.
     Avarnas/Vritas include bribe takers (those who directly/indirectly help in reducing the revenue of the State) are thieves (Rig-Veda 1-43-3). Such Avarnas/Vritas are the 5th non-divine group. Followers of the 4 divine varnas can eat and drink together (Atharva Veda 1-5-2,4). Allocation of Varnas: Chatvar Varna Ashram is based on merit, ability, capacity and aptitude. These Divine professions are allotted based on a comprehensive three tier Vedic Education System. Starting 1st with mother up to 5 years of age, 2nd with Father till the age of 8 years and the 3rd with a preceptor (Guru) from 8 to 48 years. Failure in various exams at different ages results in allocation of varnas- e.g. 1st failure results in the allocation of Shudra Varna, failure at a later age - Vaisha, still later Ribhu (manufacturer). Passing the exam at the age of 24 years- Kshatriya i.e. bureaucrats, scientists, armed forces officers, rulers etc. Those who continue Studies become Brahmins. Amongst Brahmins are Rudrai and Adityas who study up to 36 & 48 years respectively. Brahmins are priests, preceptors (Gurus), metaphysicists (risis), and philosopher cum wandering sages (Munnies). They are expert in Arts, Sciences, Military Service, Music, divine and spiritual knowledge.
     Even later scriptures like the Mahabharata, Uttha Dhyan Sutra 25-3 mentions that one is a Brahamin, Kshatriya, Vaish of Shudhra by deeds and not birth. The Bhagwad Gita 4-13 & 18- 41 to 48 maintain that the 4 orders of society are based on duties and not birth.

Examples:
1] Vyasa risi - author of the Mahabharata was born of a fisherwoman and
a Brahamin not through a recognised marriage.
2] Vishwamitra - son of a Kshatriya became a metaphysicist (maharisi)
i.e. a Brahamin.
3] Valmiki - author of a mytholigical epic was a follower of non-divine
& ignoble activities studied Vedic knowledge and became a maharisi
(Brahamin).
4] Kvaish Aylush - a maharisi and highly learned Aditya was born to a
Shudhra father and mother and became a Brahamin.
5] Kautilya made a low caste poor boy (Chandragupta Maurya) the
strongest ruler (Kshatriya) of India. In the Arthshastra, there is no
mention of Varna by birth (though in Vedas, these 4 Varnas are equal in
status, the Arthshastra cites the brahamins as the superiormost and the
shudhras as the lowest - a drift from the Vedic Chatvar Varna Ashram)

     Role of a Brahamin in Vedas is to spread vedic knowledge covering Brahama Gyan (divine knowledge of God, Soul, Spirit, matter etc), Kshatriyas to defend the society, Vaish to create material riches for the society through trade (both domestic and global) and Shudhra -unskilled workers to assist others. The Rig-Veda 10-90-1 to 6 mentions Shudras as 'of sound health, very handsome and of very high character. No varna is superior or powerful to the others. Vedas aim at egalitarian society and ensure that all 4 followers of Varna Ashram serve each other selflessly based on the philosophy of 'Idd Nan Mmam' (nothing for self-all for society). This institution started drifting first towards superiority of Brahamins in Manusmriti, Arthashastra, etc., and later by birth in Purana, tantras and interpretations by Brahamins owing to vested interests.