The long term memory of the present generation has some drawbacks.
Baddeley (1966) found that after 20 minutes, test subjects had the greatest difficulty recalling a collection of words that had similar meanings (e.g. big, large, great, huge).
http://en.wikipedia.org/wiki/Memory
Millenia ago, the Vedas were never put to writing. Hindus were supposed
recite and remember more than a million Slokas (stanzas) of the Vedas.
"The text in its surviving form was redacted in the Iron Age (c. 9th to 7th century BCE). The fixed text was preserved for more than a millennium by oral tradition alone and was probably not put in writing until the Gupta
period."
http://en.wikipedia.org/wiki/Rigveda
Since memory capabilities were gradually declining, it became necessary
to put Vedas to writing.
Ancient Europeans wrote about Ages of Man:
http://en.wikipedia.org/wiki/Ages_of_Man
There are also many other references to various
types of world ages or Ages of Man in Hopi
(worlds), Mayan (suns) and other cultures of
antiquity. Giorgio de Santillana, the former
professsor of the history of science, mentions
approximately thirty ancient cultures that
believed in the concept of a series of ages and
the rise and fall of history, with alternating
Dark and Golden Ages.
More information about these ages is available in
the Yuga concept of the Hindus:
http://en.wikipedia.org/wiki/Yuga
http://en.wikipedia.org/wiki/Satya_Yuga
The Vedas were originally conceived during
Satya Yuga when the memory and knowledge
capabilities of people were the highest. The
present age is known as the age of darkness
(Kali Yuga). Memory capabilities of common
public are bound to be low in this age.