Google "population bottleneck" and then speculate how many times that may have happened. I believe, globally, the last time it occured was the result of a supervolcano near southeast Asia. It is suggested, by the study of mitochondrial DNA and normal mutation, that there may have been as few as 10,000 surviving individuals globally. How much knowledge (and history) have these cycles taken from us?

I'd say that it hasn't been lost... But it has certainly been disregarded!

Yes, but in what was lost, not all that much of significace that influenced future events had happened. It is only that last bit right around the development of agriculture and writing when thigns woudl have started to get interestigg.

Then again with no way to record events prior to the develpment of writing systems, it could be we jus thad no reliable way to retain knowledge and we just rediscovered the same things over an dover again, gainign knowledge, losing it then regainng it and then losing it again. So, until written language came along, we coudl nto really build on our past.

That depends on how long humans have existed on earth. Have lost entire civilization and been reborn.

Shoot, I can’t remember 97% of what I did yesterday!