I would have put communciatible language at the top. Without someone or group figuring out how to use speech consistantly to relay ideas and thought so that another person could understand and continue the relay, none of those on the list would exist. Printed text and the ability to duplicate it would have to be on the list. I know most people would natuarlly think of things from the past 100 years or so and not think about the basics at the beginning. Even so,thinking of current events, the internet and microchip should be on the list. I have to make a correction, X-Ray and Double Helix DNA would exist, we just would not know about it.