Agriculture was the ultimate test of prehistoric intelligence, because for the first time humans were able to purposefully manipulate the biology of plants and animals to their advantage.  Or at least to their perceived advantage (in reality agriculture caused a lot of disease and malnutrition).

What makes agriculture so fascinating is that it’s perhaps the most basic act of intelligence that Neanderthals and early modern humans never accomplished, and thus knowing the IQ required to invent agriculture puts a ceiling on not only Neanderthal IQ, but the IQ of our own species until recently.

On page 31 of The 10,000 Year Explosion, Gregory Cochran and Henry Harpending write:

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The Eemian lasted from 130,000 to 115,000 years ago.  So for 15,000 long years,  nobody was smart enough to invent agriculture even though the climate was right.  And yet agriculture was independently invented over and over again in just the last 12,000 years.  This strongly suggests that humans today are genetically smarter than we were in the Middle Paleolithic.  The question is, did we evolve the intelligence to invent agriculture before or after we left Africa?  Perhaps we evolved it while still in Africa, and that’s what allowed us to leave Africa in the first place.

However on page 232 of Race, Evolution & Behavior (Third Edition), J. Philippe Rushton writes:

R. Lynn (1991a) suggested that although warm interglacial interludes had occurred previously, the transition to agricultural societies wasn’t possible until people became sufficiently intelligent to take advantage of the wild grasses.  According to Lynn, it was only after people had been through the last Wurm glaciation that they were cognitively able to do so.  Lynn’s view provides an explanation for why the advances were never made by Negroids or those southeast Asian populations that escaped the rigors of the last glaciation.

If agriculture was only invented by those who had survived the rigors of the last ice age, and only after they had done so,  this is strong evidence that cold winters are what selected for humanity’s high intelligence.

However this theory faced a major road block in 2003, when Tim Denham, an archaeologist at Flinders University in Adelaide, reported evidence that Papua New Guineans (who judging from their Negroid appearance, escaped the rigors of the last ice age) were practicing agriculture as early as 10,000 years ago, which predates any known southeast Asian contact.

However by 2004, a book called The Next World War: Tribes, Cities, Nations and Ecological Decline, published by the prestigious University of Toronto press, excluded Papua New Guinea from the agriculture pioneer club.  On page 50 author Roy M. Woodbridge  writes:

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If the above paragraph is true, it’s very good news for Rushton’s Mongoloid > Caucasoid > Negroid evolutionary hierarchy, because of the five independent inventions of agriculture, an astonishing 80% were by Mongoloids, 20% were by Caucasoids, and 0% by Negroids, though ironically, it was the relatively low IQ Native American Mongoloids who dominate the list.

However in the next paragraph, Woodridge acknowledges the possibility that other groups may have also independently made the Neolithic transition but the evidence is less certain:

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One reason to doubt that Africa’s Neolithic transition was independent is that it didn’t occur until 5000 BC.  What took so long?  The reason it took so long outside of Africa was that non-African modern humans didn’t have an interglacial period until the Holocene but would the ice age have equally delayed agriculture in Africa?  While tropical soils didn’t freeze, the ice age may have caused a lot of droughts in Africa.

So could Africans have independently invented agriculture once the ice age ended?  Lawyer, computer scientist, Princeton astrophysicist and best-selling historian Dr. Michael Hart writes on page 141 of his book Understanding Human History:

In neither Europe nor India was agriculture developed independently.  It has been suggested that it was invented independently in tropical West Africa and/or the Sudan but the chronology makes this highly unlikely.  We know that agriculture was being widely practiced in the Fertile Crescent by 9 kya, but it was not practiced in tropical West Africa until 5 kya.  In the intervening millennia, it had spread to Egypt (about 8 kya) and to Ethiopia, and from there across the Sudan, reaching the Western Sudan about 7 kya.

 

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