What things causes stupidity,ignorance?

[Confused Ape]

But if they had the ability to reason from the beginning, then a) why have the ability if you don't need it or have no knowledge or b) Adam and Eve were extremely stupid and were still not able to reason well :P

That just about sums up humans as a species.

The Garden of Eden reminds me of the Golden Age myths.

The term Golden Age (Greek: Χρυσόν Γένος Chryson Genos) comes from Greek mythology and legend and refers to the first in a sequence of four or five (or more) Ages of Man, in which the Golden Age is first, followed in sequence, by the Silver, Bronze, Heroic, and then the present (Iron), which is a period of decline. By extension "Golden Age" denotes a period of primordial peace, harmony, stability, and prosperity. During this age peace and harmony prevailed, humans did not have to work to feed themselves, for the earth provided food in abundance.

Hindu version.

Men neither bought nor sold; there were no poor and no rich; there was no need to labour, because all that men required was obtained by the power of will; the chief virtue was the abandonment of all worldly desires. The Krita Yuga was without disease; there was no lessening with the years; there was no hatred or vanity, or evil thought whatsoever; no sorrow, no fear. All mankind could attain to supreme blessedness.

Genesis again.

Genesis 1: 29 And God said, Behold, I have given you every herb yielding seed, which is upon the face of all the earth, and every tree, in which is the fruit of a tree yielding seed; to you it shall be for food:

Hmmm. Humans invent agriculture - "This is better than having to wander around looking for food." Once the novelty wore off and humans realised agriculture was very hard work - "It was so much better long ago. Food was everywhere. Nobody had to work because they could just reach out and pick whatever they wanted from the trees." So, the hunter-gathering way of life became equated with all food being provided by mother when humans are babies and very young children.