Human intelligence 'peaked thousands of years ago'

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Don Johnson
Human intelligence 'peaked thousands of years ago and we've been on an intellectual and emotional decline ever since'

The Independent

Steve Connor

Monday 12 November 2012

Is the human species doomed to intellectual decline? Will our intelligence ebb away in centuries to come leaving our descendants incapable of using the technology their ancestors invented? In short: will Homo be left without his sapiens?

This is the controversial hypothesis of a leading geneticist who believes that the immense capacity of the human brain to learn new tricks is under attack from an array of genetic mutations that have accumulated since people started living in cities a few thousand years ago.

Professor Gerald Crabtree, who heads a genetics laboratory at Stanford University in California, has put forward the iconoclastic idea that rather than getting cleverer, human intelligence peaked several thousand years ago and from then on there has been a slow decline in our intellectual and emotional abilities.

Although we are now surrounded by the technological and medical benefits of a scientific revolution, these have masked an underlying decline in brain power which is set to continue into the future leading to the ultimate dumbing-down of the human species, Professor Crabtree said.

His argument is based on the fact that for more than 99 per cent of human evolutionary history, we have lived as hunter-gatherer communities surviving on our wits, leading to big-brained humans. Since the invention of agriculture and cities, however, natural selection on our intellect has effective stopped and mutations have accumulated in the critical “intelligence” genes.

“I would wager that if an average citizen from Athens of 1000BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas and a clear-sighted view of important issues,” Professor Crabtree says in a provocative paper published in the journal Trends in Genetics.

“Furthermore, I would guess that he or she would be among the most emotionally stable of our friends and colleagues. I would also make this wager for the ancient inhabitants of Africa, Asia, India or the Americas, of perhaps 2,000 to 6,000 years ago,” Professor Crabtree says.

“The basis for my wager comes from new developments in genetics, anthropology, and neurobiology that make a clear prediction that our intellectual and emotional abilities are genetically surprisingly fragile,” he says.

A comparison of the genomes of parents and children has revealed that on average there are between 25 and 65 new mutations occurring in the DNA of each generation. Professor Crabtree says that this analysis predicts about 5,000 new mutations in the past 120 generations, which covers a span of about 3,000 years.

Some of these mutations, he suggests, will occur within the 2,000 to 5,000 genes that are involved in human intellectual ability, for instance by building and mapping the billions of nerve cells of the brain or producing the dozens of chemical neurotransmitters that control the junctions between these brain cells.

Life as a hunter-gatherer was probably more intellectually demanding than widely supposed, he says. “A hunter-gatherer who did not correctly conceive a solution to providing food or shelter probably died, along with his or her progeny, whereas a modern Wall Street executive that made a similar conceptual mistake would receive a substantial bonus and be a more attractive mate,” Professor Crabtree says.

However, other scientists remain sceptical. “At first sight this is a classic case of Arts Faculty science. Never mind the hypothesis, give me the data, and there aren’t any,” said Professor Steve Jones, a geneticist at University College London.

“I could just as well argue that mutations have reduced our aggression, our depression and our penis length but no journal would publish that. Why do they publish this?” Professor Jones said.

“I am an advocate of Gradgrind science – facts, facts and more facts; but we need ideas too, and this is an ideas paper although I have no idea how the idea could be tested,” he said.


Hunter-gatherer man

The human brain and its immense capacity for knowledge evolved during this long period of prehistory when we battled against the elements

Athenian man

The invention of agriculture less than 10,000 years ago and the subsequent rise of cities such as Athens relaxed the intensive natural selection of our “intelligence genes”.

Couch-potato man

As genetic mutations increase over future generations, are we doomed to watching soap-opera repeats without knowing how to use the TV remote control?

iPad man

The fruits of science and technology enabled humans to rise above the constraints of nature and cushioned our fragile intellect from genetic mutations.
Modern hunter-gatherers are retarded. If his theory is right, and if civilization/technology has been dumbing us down, then Khoisan, Amazon, Pygmy, and Papuan tribes should be owning us in brain power.

Life for hunter-gatherers didn't require more intelligence than a dog. Agriculture requires planning and problem solving, as does holding a career. The effect of needing money to survive alone has raised our IQ.
The Rambler

Modern hunter-gatherers are not indicative of the intelligence of past HGs. The remaining HGs are necessarily less intelligent than the ones who were able to domesticate animals and develop agriculture. It's not that they're dumb because they're hunter-gatherers, it's that they're hunter-gatherers because they're dumb.

Bronze Age Pervert

Modern humans are obviously inferior to those of certain ages (Renaissance Italy and ancient Greece most of all, but other ages as well). This is the cause of all the political problems you talk about.

The premise of the theory is that hunter gatherer life selects for higher intelligence, and civilization dumbs you down. Therefore Capoids and naked jungle men should be brainier than Europeans and Yellows descended from thousands of years of civilized breeding.

As for the Renaissance greats and ancient Greek philosophers; they were an elite for their day and not typical of the average person... illiterate serfs who existed to toil and die for the actual planners and thinkers at the top. 99% of people in Italy at the time of Da Vinci were raising pigs and growing just enough food that not all their spawn die in the winter.

This isn't surprising. A good book to read if you want to be dazzled by the capacious minds of the ancients is Frances Yates's The Art of Memory . Of course, before the dawn of modern technology, people had no choice but to rely on their brains to store information. You couldn't just save stuff on a portable hard disk. The brain operates like a muscle. The earlier and more rigorous the training, the greater its capabilities later; let it remain idle or fill it with garbage, and it becomes sluggish and flabby.

Bob Dylan Roof

Galton had already highlighted the intellectual superiority of ancient Athenians in the 19th century. He calculated that 1 in every 75,000 modern individuals was a genius, and that therefore there should not have been a single genius in Athens, whose population probably never exceeded 50,000. And yet there were several geniuses per generation in Athens, judging by the quality of their intellectual output.

If intelligence is a quantitative genetic trait, imagine the brilliance of the cro-magnons who were separated from ancient Greeks by more than 35,000 accumulated mutations!

6'4'', cranial capacity 200cc > modern human average, deadlifted over 1,000. Admire your pre-caucasian ubermensch:



What accounts for the so-called Flynn effect, then?

Bob Dylan Roof

improvement in phenotypic IQ

Good point. This study found a negative correlation between secular gains in IQ and general intelligence (which is the most heritable component of IQ).

'IQ scores provide the best general predictor of success in education, job training, and work. However, there are many ways in which IQ scores can be increased, for instance by means of retesting or participation in learning potential training programs. What is the nature of these score gains? Jensen [Jensen, A.R. (1998a). The g factor: The science of mental ability. London: Praeger] argued that the effects of cognitive interventions on abilities can be explained in terms of Carroll's three-stratum hierarchical factor model. We tested his hypothesis using test–retest data from various Dutch, British, and American IQ test batteries combined into a meta-analysis and learning potential data from South Africa using Raven's Progressive Matrices. The meta-analysis of 64 test–retest studies using IQ batteries (total N = 26,990) yielded a correlation between g loadings and score gains of − 1.00, meaning there is no g saturation in score gains. The learning potential study showed that: (1) the correlation between score gains and the g loadedness of item scores is − .39, (2) the g loadedness of item scores decreases after a mediated intervention training, and (3) low-g participants increased their scores more than high-g participants. So, our results support Jensen's hypothesis. The generalizability of test scores resides predominantly in the g component, while the test-specific ability component and the narrow ability component are virtually non-generalizable. As the score gains are not related to g, the generalizable g component decreases and, as it is not unlikely that the training itself is not g-loaded, it is easy to understand why the score gains did not generalize to scores on other cognitive tests and to g-loaded external criteria.'