My theory:
In ealier times, language wouldn't have been available, so word of mouth would have amounted to nothing more than various grunts. This limited vocabulary would therefore be unable to pass on historical information. In due course language would have developed to include words to mean. "Kill" and "run away". As language development progressed diferent members of the tribe could have been identified with unique "names".
It was probably a bit later than this that the concept of tense arrived into the language. (the ability to tell someone to run would have probably developed before the means of telling them when). Finally we would have had a language capable of delivering historic information. By this time Adam and Eve would have been long since gone. It therefore follows that any record of their existence would have also been lost.
Even if we were to assume that Adam and Eve arrived with a full vocabulary, why on earth would they need names? The words "YOU" and "I" would have covered every possible subject of the conversation.
Sorry, scrap that, I just remembered that they had long and meaningful conversations with the serpent.
What I'd like to know is, if they lived in the garden of Eden, who lived in the house?