There have been many accounts written about a devastating flood from ancient cultures. These vary in their details. To simplify this discussion however, I will refer to only one which was put forward several times in the past Sunday posts, the flood in the book of Gilgamesh.
Gilgamesh was a Mesopotamian king around 2800-2500 BC. In this collection of
stories, written around 2150 BC , Gilgamesh is a hero that searches for fame and immortality. In one of the quests in the book, he comes upon Ut-napishtim who was a wise man building a boat to "save the seed of all living things." Gilgamesh stayed on the boat with Ut-napishtim and his wife. Later, Gilgamesh is offered a chance by Ut-napishtim to have eternal life but because of his human weakness, he loses his opportunity. (The fact that Gilgamesh was included in the infamous flood story is a witness to his popularity, similar to Ovid including Roman emperors in Metamorphosis. )
Unlike the Genesis account of the flood which is written in a matter of fact style, Gilgamesh is written poetically probably for entertainment purposes. "The specific purpose for which (Gilgamesh) was composed is a difficult question, but the general purpose for which the epic and its constituent stories existed in oral form is very probably entertainment." Myths from Mesopotamia: Creation, The Flood, Gilgamesh and Others-Stephanie Dalley
One of the questions brought up in this discussion was which account came first, the Biblical or Mesopotamian. Gilgamesh was written down around 2150 BC while the Biblical version was written around 1500 BC. Some might conclude that because the Mesopotamian version was written first means that it is the original version.
It is evident from the many similarities in these accounts that there was a common source. The fact that many early cultures have a flood story shows that there must've been an actual flood of devastating proportions. The common source would be the flood itself.
In the Biblical account, Noah has three sons, Shem, Ham and Japheth. From these three sons arose three distinct cultures from which further cultures arose. After the Tower of Babel, the people of the earth were separated because of their different languages. (another discussion, please) Memories of the flood would've been passed down from generation to another in these different separated cultures. Different versions would naturally arise as not all people believed in God but had various beliefs.
This explains the different versions of the same story. The Hebrew race were descended from Shem from which the Biblical version of the flood would have been passed down from.
Discussing Creationism Part I