I once read a book that said a lot of the early biblical stories, Genesis and Exodus especially, can be directly correlated to ancient Egyptian mythology, just with the names of the Egyptian gods changed into the various characters in the story. And I know there was a brief time in ancient Egypt that was monotheistic, which maybe close to the time believed to be when the Hebrew people were in Egypt.
Then after putting my groceries away and getting something to eat I sat down to watch some TV. Now I prefer educational documentaries more the most part and was watching a show about the different technologies ancient cultures invented. And within the show, while talking about the process of making mummies, they said the mummies were laid out to dry with natron for forty days.
Now I'm not one for coincidences. I don't know at what time in ancient Egypt exactly mummy making was done by this process, versus when exactly the Hebrew people would have been in Egypt, if in fact they ever were, versus when Egypt experimented with monotheism. I don't know enough about Egyptian mythology to be able to speak towards any similarities with biblical stories. But to me there is definitely something going on here.
Here is one thing I do know. The first five books of the bible are traditionally believed to have been written by Moses. In Exodus it tells us that Moses was raised within the Egyptian court. He would have known Egyptian mythology better than Hebrew mythology. Now if he just happens to be trying to leave Egypt about the same time that the Egyptians monotheistic experiment is coming to an end, then it only makes sense that Moses would have wrote the stories he was more familiar with adapted for a new audience.
This may even be supported in some fashion by the biblical stories. After they fled Egypt the Hebrews got in trouble several times with their god because quite frankly they seemed to start worshipping any gods they came across. It seems to me that Moses could have easily convinced them to stick with his version of stories even if that wasn't particularly what they had believed beforehand. At this period they don't appear to be a very devoted people.