##Disclaimer The following are my own personal views, and are solely based on my understanding, I do not wish to offend anyone, this is merely a thought experiment.
##Religion is worlds first open source product
In the programming world we have the concept of open source software, where somebody writes the original code and publishes the product, people use it, add features to it when they disagree on the future of the product the product is essentially branched and eventually becomes completely different the major example of this is the well known Linux operating systems, they all origin from a core but multiple additions and multiple philosophies have created many different versions of it.
As you can see many of the distributions in the timeline did not survive the course of time and the most prominent ones were based on good ideas & good code. Which is analgous to how none of us now believes in Zeus & Thor & Orisis &
I'd like to think that religion itself is analogous to software. You can look religion as a compiled set of ideas for an attempt of explaination of the universe from the philosophical perspective. It should be noted that most religions revolve around the same core and there are many qoutes which merely sound like translations amongst the holy books of faith. I believe we can account this to the trade of the ancient world as noticed by many Arabia, India, Europe & China used to have an extremely rich trade and cultural exchange through the course of history. It is logical to think that some of these people have exchange of cultures and thoughts, like mailing lists of 1990s where like minded people could communicate, ofcourse in the ancient world this would be a slow and tideous process but we cannot deny the inginuity of humanity to explore and seek answers. I'd like to think that way in past when people used to meet some of them started to discuss about various ideas from the past and their original belief in the god. In years multiple different ideas were formed for instance the Vikings believed in human sacrifice as the christians approached the territory the ideas of a revolutionary forgiving god were accepted by many (just as you switch from windows to a Linux or Mac or vice versa).
The evidence for this are the ancient trade routes were enough for the complex ideas like mathematics and science from India to Europe, they are extremely likely to have for definite shared ideas of religion and philosophical beliefs.