Second, the ones which have similar elements are always derivative from versions first told by earlier neighboring tribes. The changes normally involve interjecting local heroes or deities into the story to make it focus upon the new group. The Biblical tale of Noah's Ark, for example, is drawn from the Sumerian epic of Gilgamesh. This also supports a scientific belief in an ice age. The major problems with equating ice ages with Flood stories are in the speed and dynamics of events that each can cause.
Glaciers advance and retreat very slowly while floods ravage the land very quickly.
The evidence left behind by each is easily identifiable and unmistakeable to geologists. And the flood story is not the only example, mind you. The two use diametrically-opposed methods to approach and describe the universe. Science approaches the issue through the use of facts, observation, experiment and reason. Religion approaches it with more concern for what sounds good and is easier to understand without regard for any evidence.