The 10,000 Year Explosion

Gregory Cochran & Henry Harpending “The 10,000 Year Explosion: How Civilization Accelerated Human Evolution” Basic Books, 2009, 251 pp.

“There’s been no biological change in humans in 40,000 or 50,000 years.  Everything we call culture and civilization we’ve built with the same body and brain.” (Stephen Jay Gould).  This is the premise the author of “The 10,000 Year Explosion” convincingly disputes, providing examples such as resistance to malaria, blue eyes, and lactose tolerance, all traits emerging in the last 10,000 years. 

The authors argue that biology explains the expansion of the Indo-Europeans, the European conquest of the Americas, and European Jews' (the Ashkenazi Jews ) rise to intellectual prominence. In each of these expansions or rise to dominance, the key was a recent genetic change: examples include adult milk tolerance in the early Indo-Europeans that allowed for a new way of life, and increased disease resistance among the Europeans settling America.

My Notes:

Pg. 1:  The author’s state it is their intention to make the case that human evolution has accelerated in the past 10,000 years, rather than slowing or stopping, and is now happening about 100 times faster than its long-term average over the 6 million years of our existence.  They dispute the claim that the ‘great leap forward’ some 40,000 to 50,000 years ago in Europe, marked the advent of cultural evolution and the end of significant biological evolution in humans.  The theory they dispute claims humans developed culture, as shown by the sophisticated new tools, art, and forms of personal decoration that emerged in the Upper Paleolithic (the span between 50K to 10K years ago). Culture then freed the human race from the pressures of natural selection: We made clothes rather than growing fur and built better weapons rather than becoming stronger. This argument that the advent of behavioral modernity somehow froze human evolution is dependent on the notion of a static environment: If a population experiences a stable environment for a long time, it will eventually become genetically well matched to that environment and changes do little to improve fitness.  However, modern humans have experienced a storm of change over the past 50,000 years.  We left Africa and settled every continent other than Antarctica.  We encountered and displaced archaic humans like Neanderthals—and probably picked up genes from them in the process. (p. 3).

Pg. 5:  Gould’s position that 50,000 or 100,000 years is an ‘eye blink,’ far too short a time for an evolutionary change, is simply incorrect.  The most accessible examples are the products of domestication of animals.  Also, evolution has taken a different course in different populations.  Over time, we have become more and more unlike one another as differences among populations have accumulated.  (Pg. 10)

Pg. 25:  It took just 10,000 years for modern humans to completely replace Neanderthals, with the last Neanderthals probably living in what is now southern Spain.  By 40,000 years ago, humans had become both anatomically and behaviorally modern.  The speed of cultural change increased by tens of times.  Favorable mutations are rare, and many of those that do occur are lost by chance.  But as human population sizes increased, particularly with the advent of agriculture, favorable mutations occurred more and more often.  Sixty thousand years ago, before the expansion out of Africa, there were approximately a quarter of a million modern humans.  By 3,000 years ago, that number was roughly 60 million.  Favorable mutations that had previously occurred every 100,000 years or so were now showing up every 400 years.

Pg. 67:  It’s probable that the evolutionary response to farming also affected the distribution of cognitive and personality traits, and that these changes played a crucial role in the development of civilization and the birth of the scientific and industrial revolutions.  Sometimes the changes, at first, required a period of adjustment.  For instance, humans who adopted agriculture shrank: Average height dropped by almost five inches.  Humans had to adapt to the new agricultural diet. (P. 76)   An example is a mutation 8,000 years ago that caused continued production of lactase and has spread widely among Europeans, reaching frequencies of over 95 percent in Denmark and Sweden.  A mutation with similar effect occurred in East Africa, so that 90 percent of the Tutsi are lactose tolerant today.

Pg. 125:  Science as we know it got its official start in Europe with the publication of Copernicus’s work De revolutionibus in 1543. The productivity and intensity of modern science far outshines earlier efforts.  Some of the most important European scientists, such as Newton, Maxwell, and Darwin, made larger intellectual contributions as individuals than other entire civilizations did over a period of centuries.  Although we do not as yet fully understand the true causes of the scientific and industrial revolution, we must now consider the possibility that continuing human evolution contributed to that process. (p. 127).

Pg. 155:  History is full of examples of human groups expanding at the expense of their neighbors.  Anatomically modern humans expanded and replaced archaic humans, the Bantu expanded at the expense of the Bushmen, and Turks and Mongols pushed aside the Iranian-speaking peoples from the steppes of central Asia. The assumption that more recent expansions are all driven by cultural factors is based on the notion that modern humans everywhere have essentially the same abilities.  That’s a logical consequence of human evolutionary stasis: If humans have not undergone a significant amount of biological change since the expansion out of Africa, then people everywhere would have essentially the same potentials, and no group would have a biological advantage over its neighbors. But, the authors emphasize, there has been significant biological change since the expansion out of Africa, particularly in those populations that have practiced agriculture.  Biological equality of human races and ethnic groups is not inevitable: In fact it’s about as likely as a fistful of silver dollars all landing on edge when dropped.

Pg. 188:  Ashkenazi Jews have the highest IQ of any ethnic group known (70% of Jews are considered to be in this group).  They average around 112-115, well above the European norm of 100.  The authors propose that the Ashkenazi Jews have a genetic advantage in intelligence that arose from natural selection for success in white-collar occupations during their sojourn in northern Europe.

Pg. 226:  With the development of agriculture, both cultural and biological evolution accelerated because that way of life made new demands on humans.  Before agriculture humans had always been foragers: The huge population increase associated with agriculture resulted in more favorable mutations as well as more new ideas.  This rapid evolution of our species following the spread of agriculture is indeed a 10,000 year explosion.  This explosion is ongoing: Human evolution didn’t stop when anatomically modern humans appeared, or when they expanded out of Africa.  Biological change has been a key factor driving history.