Judged in terms of its impact on a range of criteria, including productivity and health, refrigeration was deemed more significant than the knife, the oven, the plow, and even the millennia of selective breeding that gave us the livestock, fruits, and vegetables we recognize today. It is also a much more recent development: our ancestors learned to control fire before modern humans even evolved, but our ability to command cold at will dates back little more than 150 years.
