This idiotic narrative is based on a very popular fallacy -- that we are not capable today of building what was built in the past, so how could our ancestors possibly have built these things? You run into this idea again and again in pop anthropology and New Age theories about the history of mankind. It is a fallacy because our ancestors had skills we do not develop, such as the shaping and moving of large blocks of stone. We have other skills that they did not develop, such as bonding composite materials. Our ancestors were not stupid. Their brains were about the same as our brains today. They relied less on writing and more on memory than we do. They had associations or guilds of extremely skilled craftsmen who excelled in the working of stone, glass, metals and wood. We rely more on machines than they did -- they used simple tools, but they did amazing things with them. They couldn't build the Hoover Dam, but they could build the pyramids (although, you could make a good case that the ancient Romans could have built the Hoover Dam).