Of the historically great inventions of mankind, a short list is possible. First are fire and sharp objects. I was going to make the list longer but realized that with only these two implements the bulk of our ancestors traversed the time span of 500,000 years ago to 20,000 years ago, all on the weight of two accessories.
For accessory efficiency this is pretty good. Somewhere of half a million years of evolution from savannah children to neander and cro-magnificent, to the sapiens dude powered by two lousy appliances.
The question is what’s next on that list? What follows fire and sharp objects to making human animals smart? I admit to having a farm-kid perspective on this third great leap for homo-type guys, my guess is mittens.