A question was asked in the Common Misconceptions of Christianity post. "If you think something is myth, fine. It's another matter to show why; to point out mythological development, and demonstrate the literary genre under consideration is mythical." The answer to this challenge is one that will take more time and space than a retort deserves. For those that don't know some of what I'm about to lay out, burying it in a response seems to be a disservice to the information and theological understanding. So, here is a blog answer.
Many myths of creation and gods existed before any Hebrew traditions existed independently. One of the the gods was Ra whom was the creator of everything, born out of 8 other gods.All of them together were known as Ennead, much like God is made up the father, the son and Holy Spirit. Three beings equal one. Ra was prominent about 2500 BC, or 1500 years before any Hebrew writings existed. Clearly this was a story prior to Yaweh of the Old Testament as most of those writings became common place about 600 BC.
Egyptians believed that there was a universal flood. Eventually a mountain arose from the waters and the creation of life took place there. Some say it was Ptah who "spoke" Atum (a sun god) from the flood waters. Others believe that 8 gods arose from the waters and gave birth to Ra whom then started creation. There were a number of these different myths that were all similar in nature. The word had spread to each locale and slight variations on them came to be. Remember that much of this would have been spoken word and not down in writing. If you've ever taught a class, you know that people will hit you with oddball questions. If you didn't have a source to refer to, making it up to appease the listener would have been common. The new version is what would march on in history.
If you get into Old Testament study, you'll learn that there are different documents of the Books of Moses. The common lay assertion is that Moses wrote the first five books. This is patently absurd as the books speak of Moses' death, burial, and his body never being found and then continue on telling more. If it were clear that there was another author, an argument could be made for this. But the style of writing doesn't change, so there is no reason to assume new authorship. Even to say that his body was never found, over 50 year spans you can see language differences. eg Who's says groovy anymore unless it's in jest? It's all balderdash.
So what you really end up discussing are the J, E, P , and D documents. Each one refers to geographical areas of influence. These different areas of influence lead to the contradictions that you find in the Old Testament. For example, Genesis 1 says that man was created after the animals and Genesis 2 says that god formed the animals then brought them to Adam to name them. The sorting of these things out isn't relevant, but clearly through out the Old Testament, we find different versions of the same story. If it were a story being related by man from God, why the differences? Each geographical area that influenced the different documents have historical differences that correlate appropriately and predictably. I would hold Joseph Smith to the same standard for having read the Gold Plates differently. If it's absurd in one, then it's absurd in the second case too. Either the story was accurate or it's false and there should be few differences.
Aside from the contradictions and how each area of Egypt and Babylon saw the creation myths, what is similar that can be pointed to? How about the flooded earth that in the Bible is "formless" with "darkness below the deep"? That's remarkably like the creation stories that one would find in Egypt. As you dig into this thought, Genesis 1:9 also shows a flooded Earth at creation."And God said, “Let the water under the sky be gathered to one place, and let dry ground appear.” However, you have multiple gods in the Egyptian stories and clearly that's distasteful when you are trying to worship the one true God. But polytheism is a problem in the Old Testament as well. Genesis 1:26 “Let us make mankind in our image, in our likeness," Who is this "us" and "our" if God is a singular being? Is the trinity different than Ennead? Sure you might suggest that it's the Holy Ghost and Jesus, but look at the whole of the context. We are talking about a culture the neighbors Egypt. They really don't have a history of writing much before the Old Testament. The stories are lining up as close conglomerations of the story of Ra as told in different areas. It's so discernible that scholars study the texts as different documents rather than books of the Bible. The context really points to a borrowed myth from the origin.
So how much further does this go? Ra later merges with another god named Horus. That sounds familiar right? Father and the Son in one? Horus was the child of Osiris and Isis whom are all a part of the earlier 8 gods (sometimes called 9) that I mentioned that gave birth to Ra. So Ra-Horus is his own father. Set, one of those gods whom was the god of Chaos (I hear the Devil), killed Osiris (his brother. anyone hear Cain and Able?). Isis manages to put Osiris back together except for Osiris' penis. She fashions him one out of gold. She gets pregnant then flees Set for her and Horus' safety. So Horus is virtually born immaculately as no dirty penis created him (Mary). His mother is fleeing for safety like Mary from King Herod.
Clearly there are parallels that run deep. Culturally you have two neighbors, one whom could write influencing the other. Have I presented anything conclusive? Nope. But here's the deal. Is my scenario more likely and believable and supportable than a people independently coming up with a deeply similar story on their own and that story being the one of the true god versus it just being a continuation of a mythical god(s) and creation?
Religious Tolerance Chart of Jesus and Horus Comparison
Much of the information in this argument comes from the book 101 Myths of the Bible written by Gary Greenberg, President of the Biblical Archaeology Society of New York