Cochran and Harpending put forward the idea that the development of agriculture has caused an enormous increase in the rate of human evolution, including numerous evolutionary adaptations to the different challenges and lifestyles that resulted.

These may include tendencies towards (for example) reduced physical strength, enhanced long-term planning, or increased docility, all of which may have been counter-productive in hunter-gatherer societies, but become favoured adaptations in a world of agriculture and its resulting trade, governments and urbanization.

The authors speculate that the scientific and Industrial Revolutions came about in part due to genetic changes in Europe over the past millennium, the absence of which had limited the progress of science in Ancient Greece.

The authors suggest we would expect to see fewer adaptive changes among the Amerindians and sub-Saharan Africans, who have farmed for the shortest times and were genetically isolated from older civilizations by geographical barriers.

Cochran and Harpending concentrate on the Neolithic farming revolution as the beginning of major population expansions that provided enough mutations to accelerate genetic change.

The origins of many recently adapted genes have now been traced to this period, creating effects such as regional differences in skin colour and skeletal gracility.

[1] Research cited by Cochran and Harpending provides evidence of genetic mixing between modern humans and an ancient Homo lineage such as the Neanderthals.

As anatomically modern humans emerged from Africa and spread across the globe, the "indigenous" Homo populations they encountered had already inhabited their respective regions for long periods of time and might have been better adapted to the local environments than the colonizers.

It follows, it is argued, that modern humans, although probably superior in their own way, could have benefited from adaptive alleles gained by interbreeding with the populations they replaced, as was proposed to be the case for the brain-size-determining gene microcephalin.

He goes on to state that where Diamond was content with environmental determinism, at times opposing the roles of human biology and population differences, Cochran and Harpending embrace them both.

The first seeks to resolve a longstanding debate in historical linguistics by making a case for the Kurgan hypothesis on the origins of the Indo-European language group.

Drinking milk, from cows, horses, or camels, is a behavior shared by many of history's greatest conquering peoples, whether Kurgans, Scythians, Arabs, or Mongols.

"[16] According to the Southern Poverty Law Center, these claims were based on the work of discredited psychologist and antisemitic conspiracy theorist Kevin MacDonald.

[1] In New Scientist, Christopher Willis wrote that the "evidence the authors present an overwhelming case that natural selection has recently acted strongly on us".

[18] In Evolutionary Psychology, Gregory Gorelik and Todd K. Shackelford wrote, "Although many of their arguments need more fleshing out and some may not withstand the assault of further scientific analysis, the authors are stunningly creative when considering human history.

If even a handful of their arguments survive the onslaught of rigorous scientific scrutiny, Cochran and Harpending will have offered a valuable and novel approach to addressing questions of recent human evolution.

"[19] In Evolution and Human Behavior, Edward Hagen wrote that the book makes "many unsupported and often questionable assertions", but it is nevertheless valuable in raising "bold questions about major historical encounters between populations — Neanderthal and modern humans, German tribes and Romans, Europeans and Native Americans — in light of formidable (but not unassailable) arguments from population genetics".

[21] Evolutionary anthropologist Keith Hunley, writing for the Journal of Anthropological Research, described the book's thesis as interesting, but said the list of behavioral adaptations supposedly favored by agricultural lifeways was "bizarre".

Hunley specifically criticizes the last chapter on Ashkenazim for being based on shoddy or fabricated data, and for failing to mention the human suffering caused by pseudoscientific racism.