No alien technology needed. The people before us were just as smart as us. They had different tools and knowledge, but they were just as smart, often, smarter.
Technology lost is maybe more than technology discovered?
Actually, people back then must have been brilliant compared to today, somehow, they managed to quarry stones that weighed multiple tons, transport the for miles and then stack them on top of each other multiple stories high and did it all without modern heavy equipment.
I recall reading many moons ago about the idea that there is some kind of degradation in each generational replication that is dumbing us down.
Agreed. As a young man I heard the theory that man has always been intellectually the same throughout the ages. The only thing that has really changed is the technology. Technology is where evolution truly exists.