Manusrumiti says:

As the son of Shudra can attain the rank of a Brahmin, the son of Brahmin can attain rank of a shudra. Even so with him who is born of a Vaishya or a Kshatriya
More Facts:

The caste system is perhaps the most elaborate expression of institutionalized oppression ever built by human beings. Caste oppression is so similar to racial oppression that the Dalits, the people once referred to as “untouchables,” by the supremacist arrogance of Brahmins (the priestly caste), are demanding that the UN Conference against Racism also include a discussion of Hindu racism. This of course draws outraged responses from the arrogant upper caste leadership of the neo-Brahminial Hindutva movement. This movement is striking terror on India’s Muslims, and Christians and is not interested in any form of democratic society, but on that is built on Hindu supremacist ideas. Hindu racism is so encoded within the so-called Hindu dharma (‘law’) that most Hindus tend to feel outraged even though they know that the practices and ideologies of caste and race intertwine and overlap like strands of the same fiber. More than 300 million (yes 300 million!) human beings in India live lives as bonded laborers. This is modern day slavery. A vast majority of them are Dalits and people of the lowest castes in the caste hierarchy. For them life under Hindu “dharma” is one of always serving Brahmins and upper castes, and doing the most menial tasks in society, a degrading condition justified in Hinduism as one appropriate to their caste! There is no economic, political or cultural emancipation for these oppressed millions under the regime of Hindu dharma, and with the rise of the Hindu fascist movement represented by the BJP government, they along with hundreds of millions of Muslims and Christians are being targeted and attacked.
Dsjeya? anyone? I hope some of my hindu friends can explain it to me.