The history of Hinduism is unique among the world religions in that it has no founder or date of origin. While most major religions derive from new ideas taught by a charismatic leader, Hinduism is simply the religion of the people of India, which has gradually developed over four thousand years. The origins and authors of its sacred texts are largely unknown.
Although today's Hinduism differs significantly from earlier forms of Indian religion, its roots date back as far as 2000 BC, making it one of the oldest surviving religions. Because of its age, the early history of Hinduism is unclear. The most ancient writings have yet to be deciphered, so for the earliest periods scholars must rely on educated guesses based on archaeology and contemporary texts.
In the last few decades, the history of India's religion has also become a matter of political controversy. The history of any nation (or individual) is an important part of its self-identity, and this is especially true of India, which so recently gained independence after centuries of colonial rule. The controversy over India's history centers on the origin of the Aryan culture, as we shall see in more detail below.
The Hindu religion: past and present
The Indus River Valley Civilization
In 1921, archaeologists uncovered evidence of an ancient civilization along the Indus River, which today runs through northwest India into Pakistan. The so-called Indus Valley civilization (also known as the "Harappan civilization" for one of its chief cities) is thought to have originated as early as 7000 BC and to have reached is height between 2300 to 2000 BC, at which point it encompassed over 750,000 square miles and traded with Mesopotamia.
Some writings of this period has been discovered, but unfortunately in such small amounts that they have yet to be deciphered. Knowledge of this great civilization's religion must therefore be based on physical evidence alone. Baths have been found that may indicate ritual bathing, a component of modern Hinduism. Some altar-like structures may be evidence of animal sacrifice, and terracotta figures may represent deities. An important seal features a horned figure surrounded by animals, which some conjecture is a prototype of Shiva, but it could be a bull parallel to that found on Mesopotamian seals.
The Controversial Aryans
The Indus Valley culture began to decline around 1800 BC, due possibly to flooding or drought. Until recently, it was held that the Aryans (an Indo-European culture whose name comes from the Sanskrit for "noble")  invaded India and Iran at this time. According to this hypothesis, both the Sanskrit language and the Vedic religion foundational to Hinduism is attributable to the Aryans and their descendants. The original inhabitants of the Indus Valley are thought to have had a Dravidian language and culture, which became subordinate to that of the invading peoples.
Proponents of this hypothesis point to similarities between Zoroastrianism (the ancient religion of Iran) and the Vedic religion of ancient India, as well as similar finds in ancient cemeteries in modern-day India and Tajikistan and Uzbekistan. In addition, no trace of horses or chariots have been found in the remains of the Indus Valley culture, but were central to Aryan military and ritual life.
Since the 1980s, this "Aryan Invasion" hypothesis has been strongly challenged as a myth propagated by colonial scholars who sought to reinforce the idea that anything valuable in India must have come from elsewhere. Critics of the hypothesis note that there is lack of evidence of any conquest, among other historical and archaeological problems. One alternative hypothesis is explained by Encyclopædia Britannica as follows:
Between about 2000 and 1500 BCE not an invasion but a continuing spread of Indo-Aryan speakers occurred, carrying them much farther into India, to the east and south, and coinciding with a growing cultural interaction between the native population and the new arrivals. From these processes a new cultural synthesis emerged, giving rise by the end of the 2nd millennium to the conscious expressions of Aryan ethnicity found in the Rigveda, particularly in the later hymns. The 19th-century Aryan Invasion theory has generally been abandoned as inaccurate, but most scholars do not reject the notion of some outside influence on the Indus Valley civilization. For many, it is a political issue as well as a historical one, with the original theory is regarded as racist and offensive. BBC Religion & Ethics summarizes the matter this way:
Many people argue that there is now evidence to show that Muller [original proponent of the hypothesis], and those who followed him, were wrong. Others, however, believe that the case against the Aryan invasion theory is far from conclusive.
- - "History of Hinduism." Encyclopædia Britannica (Encyclopædia Britannica Premium Service, 2004).
- "Indian Religions and the Hindu Tradition" The Cambridge Illustrated History of Religions (Cambridge University Press, 2002).
- "Aryan." Encyclopædia Britannica (Encyclopædia Britannica Premium Service, 2009).
- "India » History » India from the Paleolithic Period to the decline of the Indus civilization » Post-Harappan developments » The appearance of Indo-Aryan speakers." Encyclopædia Britannica (Encyclopædia Britannica Premium Service, 2009).
- "Hinduism: History: Aryan Invasion Theory" - BBC Religion & Ethics