90% of all humans who have ever lived were hunter gatherers

From Humankind by Peter Farb, page 89.

Perhaps a total of 100 billion humans have walked the planet since the appearance of the earliest hominids. Of these, about six per cent have been agriculturalists, fewer than four per cent have lived in industrialized societies, and all the rest - approximately ninety per cent - have lived as hunters and gatherers. Only during the past 12,000 years in a few places, and for less than 5000 years in most of the world, have humans domesticated plants and animals, lived in settled villages, developed complex societies, and harnessed other sources of energy besides human muscle. The 12,000 years since the earliest agriculture represent only about 500 human generations, surely too few to allow for overwhelming genetic changes. Therefore the origins of the intellect, physique, emotions, and social life that are universal to human beings must be traced to preagricultural times. Humans are the evolutionary product of the success of the hunting adaptation, even though almost all of Homo sapiens alive today have abandoned that way of life. The traits acquired over millions of years of following this adaptation continue to provide the basis for human adjustment to the modern world. Still influencing us today is the fact that hunting and gathering is more than simply a particular means of subsistence. It is a complete way of life: biologically, psychologically, technologically, and socially.

Farb published this in 1978 and in the intervening 34 years, our knowledge has advanced. We now know that evolutionary adaptations can pop up in short time frames. The mutation for blue eyes is believed to have occurred in the region of the Black Sea 6-10,000 years ago and has now spread to some 50% of all Europeans and their descendants (though no one knows why it has spread so quickly, it is unclear whether or what survival benefit it yields). Similarly, lactose tolerance emerged in northwestern Europe only some 7,000 years ago and has proved a very successful adaptation. So we now know that advantageous mutations can and do spread very quickly.

All that said, Farb's key point remains valid. The bulk of our adaptive responses are buried in the 90% of our history as hunter gatherers.