In an oral culture — one that is not written down — mythology evolves as it is passed from storyteller to storyteller. The Jesus myth was created in exactly this way, pasted together from earlier sources. This process is called ‘syncretisation.’
There is no fixed record of an oral tradition, by definition. In an oral culture or tradition, myths grow and develop to reflect the lived experiences and cultures of the people telling them. It was only when writing was invented that these traditions could be codified and by that time, they had been evolving for thousands of years. This means that there are many versions of the same myth, as different peoples carried it forward.
So we cannot say that, because detail differences exist between two similar myths, they are different or have different origins.
The cities of Sumer had been established for over a thousand years by the time the Epic of Gilgamesh was written, circa 2500BC, but they did not control all of the land. Most of it remained uncultivated and taming the wilderness, to make more commercially productive farmland, became important to the cities. That required an ever-increasing labour force, which could only be achieved through the enslavement of men.
Civilisation depends on the enslavement of men.
Many early civilisations were built on the enslavement of men, in the sense that we now understand it, but others were either not slave states or were only partially so. So how could the enslavement of men be effected, other than by force?
One answer is illustrated in two great tales: The Epic of Gilgamesh and Genesis. The enslavement of men to the city was brought about not through violence, but through love, or at least, lust.