Archeological digs that showed women and children’s graves which were larger and far more elaborate and ornate than mens.
I don’t know, initially I found this assumption made on the basis of the above discoveries quite bizarre. However the author ends up explaining it and throwing in other artifacts and such that makes it seem plausible…these arguments he makes in favor of powerful matriarchies. However all this is largely speculation based up archeological discoveries of stuff. There are no written records or any other sort of proof beyond the artifacts to suggest that women were heading up early human communities (prior to civilization as we know it.)