Answer: Accounts of the deluge and the issue of the human race from one family are not limited to the Bible. Ancient eastern writers confirm the account of Moses even to the sending forth of the birds.
Traditional mythology of Egypt, Greece, and all the neighbouring countries preserve the various facts and words connected with the flood. A sacred ship is carried in procession in many places, and the word ‘ark’ is used for a place of protection (Moses, the Ark of the Covenant). Eight persons were saved and eight has become a ‘lucky’ number in the Middle and Far East.
The East preserves the general historical account that the various colonies of the human race stemmed from Noah. In Greece and elsewhere history starts with the first king of the appropriate colony, but associated with a ship.
[The Chinese Miao Legend states that a single human couple escaped the deluge in a wooden drum, and then gave birth to the first members of post flood humanity – Sosthenes from RL Hales http://creationism.org/csshs/v06n2p04.htm]
After the deluge the population of the earth must have increased rapidly, indeed amazingly fast, in proportion to the space over which the population spread.
So hardy deniers of the flood simply expose their desire to raise objections for their own sakes.