As the glaciers of the last ice age receded 12,000 years ago, a wave of illness swept the globe. The cause was the shift from a relatively healthy foraging lifestyle to a more dense and sendentary agricultural lifestyle.

Before then, human infections tended to be mild and chronic in nature.. full-time agrarian living brought the kinds of acute and virulent infections we're familiar with today.

This was the first of three major epidemiological shifts in human history. The cause was not farming, but the lack of dietary diversity, the density of human and animal habitation, and the increase in social inequality and poverty.

These changes reversed in the 19th and 20th century, but — surprisingly — before the discovery of antibiotics.

Health improvements were mainly due to nonmedicinal factors such as better farming and food distribution methods, major sanitation projects and housing reforms in poor areas.

This is known as the "Mckeown Thesis," and it remains hotly debated today. (This adds further interest to the idea that the Industrial Revolution was primarily driven by natural climate change.)

Social changes alleviated the crowding and poverty caused by the Neolitic Revolution in the first place. This was "a significant but only partial reversal of the changes that first began in the Neolithic period."

At the same time, heart disease and cancer increased, and many of the health problems persisted in less developed countries, anticipating the third shift: the emergence of a "global disease environment."