It would have to be a metaphor, as genetically, the offspring of Adam and Eve couldn't have populated the world without humans suffering serious inbreeding problems! Similarly, Mr & Mrs Noah and their sons & their wives would've been hard put to do it either. (We're told they were the only survivors of The Flood.) Similarly the 'two by two' animal species couldn't have restarted the entire fauna of the Earth. It so obviously isn't literally true.