Given the time scale that we have been able to document the living human body, both inside and out, there isn't enough information to give you an answer.
What you are asking is like taking War and Peace, opening it up to a random page, showing a student a single letter on the page, then asking them to explain how it began and ended.
Now to take this further. A priest, not knowing, would make up a story and assert that it must be right, where as a scientist would start to read the book to find out. Given enough time, who's account would you trust?
As a species, we've just started reading the book of life. You can either start reading for yourself, or walk over to the fiction section and pick whatever sounds pretty to you. You can assert that it must be true because it has a beginning, an end, and a pretty cover.