There are several reasons why prehuman civilization is kept secret by ruler of this world. One of them is to avoid warfare between those who can and those who can't accept that humans are descendants of something else.

Analogy of scientist who try to reach the higher speed:
A child ant is tired after the long walk in a body of a jet.
It tries to find a method of traveling faster than walking.

People usually feel funny, smile and laugh when I tell them
about my strong belief in the very existence of prehistoric
advanced technology and great civilizations of wilier races.
I just can't wait to see their faces at time the truth is revealed.

There are many things in life that can only be really understood after we have become parents who have offspring.

If alien races have interbred with human kind since long time ago, then there is no need to look for them outside us.

Science is a trigger of changes of civilization. Religion is the failsafe of science performance.