So far in this series, I've introduced the Dalits and talked "a little" about the caste system in India. Today I want to address the history of caste in India, or the "where it came from" question.
The area we consider to be northern India was settled earlier than 2,300 B.C. by a group of people known as the Harappans. The Harappa civilization was relatively advanced, and from this group the roots of Hinduism first formed. This civilization lasted until, for some reason I haven't yet found, it began fading out in about 1,700 B.C. This left a vacuum into which a group known as the Aryans moved in circa 1,500 B.C. These Aryans were cattle farmers, and came into India from the northwest looking for new territory on which to raise their cattle1. The Aryans, by most accounts, formalized the initial caste structure as a way to control the indiginous peoples, and to separate the native Indians from the conquering Aryans2.
The initial caste structure was not as rigid as it would later become. There were three main caste groups at first, and as the Aryans moved southwards and conquered additional peoples, the two lowest groups (the Shudras and out-castes - now Dalits) were brought into the caste system3. The Aryans used caste to strengthen their power, and keep the native Indians (Dravidians) under their thumb. The Aryans, too had lighter skin color, which made higher caste members physically identifiable4. Race was a differentiating factor in caste.
Over the next millenia or two, India dealt with wars and changes of control, seeing Greek and Pandyan rulers, as well as Indian rulers. In the 3rd - 5th centuries A.D., the Gupta dynasty emerged, and it was at this time that the caste notions of purity and the diminished role of women were developed5.
Since that time, the caste system has remained fairly stable for a couple of reasons. First, the Hindu notion of karma served to act as a control by teaching caste members that their lot in life was determined in earlier lives. If they obeyed their dharma in the current life, they could be reincarnated as a higher caste member. Second, the higher caste members controlled the military, the leadership and management of the company, as well as the educational insitutions. They were able to maintain control by enforcing discrimination and strict control of power. Religious teachings of Hinduism were used to successful effect by higher castes who used the myriad gods of Hinduism and caste divisions to keep the castes separated and unable to unite against those in power.
This is not to say there weren't attempts to change the caste system. Various attempts were made by individuals and groups, especially from other faiths, to break the cycle of oppression of lower castes. Buddha and Mahavira (founder of Jainism) fought caste in the 6th century B.C., for instance6. However, even the majority of those in other faiths (like Christianity and Islam) did not rebel against caste. Many Christians and Muslims, even those who converted from Hinduism, embraced the structure of caste. And while the British did reduce some of the more egregious problems of caste (such as, sometimes and not universally, sati), they did not eliminate caste altogether.
So for the better part of two millenia, caste remained fairly stable. Then, in the first half of the 20th century, during India's last decades before independence, Dr. B.R. Ambedkar, a Dalit activist, became a driving force in the fight for equal rights for Dalits. Despite persecution, he was able to rise to a position of prominence, and in large part because of his work the Indian constitution included legal protections for the Dalits; legally, persecution was no longer permitted. Realistically, though, caste discrimination has remained in place, and even among those Dalits who've managed to rise above their station have faced persecution. In recent years, more Dalits have started leaving Hinduism as the priests of the faith have retained the historical teachings that the Dalits are not even worthy of the gods' attention.
As with all things history, this summary leaves gaps, and there are some discontinuities I've found in my readings. Some historians tend to discount the impact of Aryans, saying caste was already in place ca. 1,500 B.C. Others have emphasized (or criticized) the role of Mahatma Gandhi in fighting for Dalit rights. But for the most part, what I've outlined above is described most consistently. At the least, hopefully this puts some context around the caste system: a division of people, millenia old and stable for at least two thousand years, heavily influenced by religion, and based in part on race and gender.
1 - Culture Shock! India - Gitanjali Kolanad, 2001 (ch. 1). Note: There is some dispute over both the nature of Aryan culture and the migration of Aryans into India itself.
2 - http://uwacadweb.uwyo.edu/religionet/er/hinduism/HORGS.HTM
3 - ibid
4 - Culture Shock! India - Gitanjali Kolanad, 2001 (ch. 2)
5 - Culture Shock! India - Gitanjali Kolanad, 2001 (ch. 1)
6 - Culture Shock! India - Gitanjali Kolanad, 2001 (ch. 2)