Evolution of Hinduism
Back in 4000 BC Indus Valley civilization was thriving, inhabited by Dravidians. There's a big school of people who believe that Indus Valley was actually inhabited by Aryans and that they just moved to the Ganga valley over the years. I wouldn't really care what really happenend to those guys but the more popular story of Aryan invasion on Dravidians makes more sense to me.
Indus valley people were known to worship Pasupathi- a primitive form of Shiva. They also worshipped the forces of nature. They would be what the church would call "Pagan"s about 4500 years later. Now Dravidians have always been more worshippers of Shiva than Vishnu. It is no coincidence that the Rakshashas also invariably worshipped Shiva and got all kinds of boons from him in the Indian Mythology. Vishnu would come up with innovative ideas to hit at the flaws in the boon, given by Shiva, to kill the rakshasas. Aryans worship forms of Vishnu more. But there are exceptions to both the rules.
So I would believe that the valley was actually inhabited by pasupathi worshipping Dravidians who were invaded by "Vishnu" worshipping Aryans. Now this was a slow process and there was quite some interaction between the two communities. One fine day an old wise grey headed Dravidian and the "pasupathi chair professor of divinity" met the Aryan equivalent chair professor when having their daily dosage of panipuri at their favorite chat bandar. Soon the discussion led to their beloved Gods. They exchanged their stories and luckily for mankind back then there was no concept of religion and people were more liberal and accommodating. They both worked for several days and nights from then on to come up with a convincing story intertwining all their Gods. Both these guys were already experts at this art. The Dravidians have met several tribes which worship different forces from nature. And each time they meet a new tribe they get a new God. Same with the Aryans, they have traveled a long way from what would be Hitlers Germany all the way to India. So they have encountered among other things people who worship tortoises, fish, pigs etc and had to accommodate each of their stories.
The Aryans solved this problem smartly by hitting at it the object oriented way, which in later years was popularized by java. They have created a class of Vishnu who can have numerous instances, avatharas(incarnations). So each time they came across a powerful tribe, Vishnu would get a new avatar. Dravidians had to build a story around Shiva, and his family to accommodate the Gods. Among other things they found a elephant worshipping tribe. Dravidians the original inhabitants of the Indus Valley have not traveled as much as the Aryans. So their school has lesser number of Gods.
Now going back to our chair professors, they have struggled for several days and finally came up with a convincing story which gives equal importance to both the Gods. And they looked forward and included another God at the same level to accommodate any new powerful tribes. Thus we got our trio the "trimurthi" Brahma, Vishnu and Maheshwara(Shiva or pasupathi) who represent the creator, the preserver and the destroyer respectively. Then they had a hierarchy of Gods with a relative importance proportional to the tribes political and economic strength. They pulled off by far the biggest merger ever, demographically, involving about 10 million people. It has largely proved to be successful even to this day with over a billion people. But it had its problems in the journey.
As the Dravidians started moving down south, they encountered more and more tribes and Gods. Now the people started suspecting the authenticity of their religious experts who keep increasing the number of gods and come up with new, ridiculous stories which contradict from place to place. The Aryans who started settling in the Ganga valley also had the same problem. Having sensed the restlessness among people, the experts called for a giant spiritual conference with representatives from all around India.
They all sat on the sacred banks of Ganga to decide the future course to reinstall faith and the spirituality among the people. They started a brain storming session and people started throwing out ideas left, right and center. They resolved many contradictions and standards started evolving. It was decided that everyone has to stick to the standard story. When they broke for lunch someone mentioned the new best selling novel in the market, Ramayan. Luckily for them the author, Valmiki, was at hand. They liked the character of the Hero and decided to make him an incarnation of Vishnu. The author was asked to change the book slightly and write a supplementary Uttar-Ramayan to reinforce the fact that Rama was a God and an incarnation of Vishnu. Rama the ideal man would be their new weapon to reinforce the faith.
Another attraction at this particular congregation was this young budding and very promising writer Vyasa. He's shown a lot of promise and has already proved himself with his oral work, Vedas, which the congregation adopted as the sacred word of God. He also won the contract to write the story of Vishnu's next avatar.
The other big problem they had to address was the growing number of Gods. Unfortunately for them the people were good at counting and they didn't like the idea of Gods growing faster than the population. So the congregation came up with a game plan to tackle this situation. They have decided to give people the largest number, any of them could count, and tell them that it is the number of Gods. Remember...., the decimal system was not in place back then and a fairly good mathematician like Gauthama Siddhartha(Buddha) who came in around 300 BC can count only upto 10,000 using some funny symbols. They fixed the number at 3,00,000. There were only 4 people in the world who could count upto 3,00,000. However they were smart not to make it very clear to the general public and wrote down all the rules in complex Sanskrit, so as to avoid the fools from reading bits and parts and questioning the obvious. They made the verses ambiguous enough so that the future generations can even find "E = mc squared" in them. Similarly the number can be interpreted in several ways and was thought to be around 3,00,000 for a long time. They were able to fit in all the Gods they came across as well as their brothers,sisters, wives and children into the club of gods very safely without crossly the numerical limit.
All was well until this guy Brahmagupta came along with the decimal notation. Now he can denote numbers infinitely long. Brahmagupta who can think well out of the box and would have made a good Microsoft employee, began questioning the number of Gods again. This troubled the spiritual authorities again as now they have to place a clear number with no ambiguity. They decided on the number 3 crores , equivalent of their projected population of the world for the year 10,000 AD. Little did they know, the zero and the decimal notation are going to change the world forever.
Thanks to the large buffer, we still have a large number of positions vacant to accommodate for new Gods. But unfortunately somewhere inbetween, the concept of religion was born.