Scientists say that we have much smaller brains [2] than our ancestors had 20,000 years ago [3] … and we might have gotten stupider since agriculture became widespread [4].
Huffington Post reports that we've probably gotten dumber than even our Victorian ancestors [5]:
A provocative new study suggests human intelligence is on the decline. In fact, it indicates that Westerners have lost 14 I.Q. points [6] on average since the Victorian Era.
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As for Dr. te Nijenhuis and colleagues, they analyzed the results of 14 intelligence studies conducted between 1884 to 2004, including one by Sir Francis Galton, an English anthropologist and a cousin of Charles Darwin. Each study gauged participants' so-called visual reaction times -- how long it took them to press a button in response [7] to seeing a stimulus. Reaction time reflects a person's mental processing speed, and so is considered an indication of general intelligence.
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In the late 19th Century, visual reaction times averaged around 194 milliseconds, the analysis showed. In 2004 that time had grown to 275 milliseconds. Even though the machine gauging reaction time in the late 19th Century was less sophisticated than that used in recent years, Dr. te Nijenhuis told The Huffington Post that the old data is directly comparable to modern data.
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This new research was published in the April 13 issue of Intelligence.
The Daily Mail notes [8] that we've gotten dumber since the 1950s:
Richard Lynn, a psychologist at the University of Ulster, calculated the decline in humans’ genetic potential.
He used data on average IQs around the world in 1950 and 2000 to discover that our collective intelligence has dropped by one IQ point.
Dr Lynn predicts that if this trend continues, we could lose another 1.3 IQ points by 2050.
What's Making Us Dumber?
There are several theories for why we are getting dumber, including the following:
(1) Toxic chemicals in the environment can reduce intelligence.
Modern man is surrounded by toxic chemicals which have been shown to reduce intelligence. Examples include flame retardant [9], lead [10] (found in many lipsticks [11]), certain pesticides [12] (and see this [13] and this [13]), fluoride [14] (more [15]).
Radiation can also reduce intelligence [16]. For example, radiation can reduce brain size [17].
Brian Moench, MD notes [18]:
Many epidemiologic studies show that extremely low doses of radiation increase the incidence of ... diminished intelligence.
And a very well-established resource for doctors (the Merck Manuals) state [19]:
The fetus is sensitive to damage from radiation because fetal cells are dividing very quickly and also differentiating from immature into mature cells. In the fetus, exposure in excess of 300 mGy during 8 to 25 weeks after conception may cause reduced intelligence and poor school performance.
(2) Humans evolved to eat a lot of Omega 3s [20]:
Wild game animals have much higher levels of essential Omega 3 fatty acids than domesticated animals. Indeed, leading nutritionists say that humans evolved to consume a lot of Omega 3 fatty acids in the wild game and fish which they ate [21] (more [22]), and that a low Omega 3 diet is a very new trend within the last 100 years or so.
In other words, while omega 3s have just now been discovered by modern science, we evolved to get a lot of omega 3s … and if we just eat a modern, fast food diet without getting enough omega 3s, it can cause all sorts of health problems.
So something just discovered by science can be a central fuel which our bodies evolved to use.
Omega 3s - in turn - boost intelligence [23] and help prevent cognitive decline [24].
(3) Similarly, Science Daily notes [25]:
Exposure to specific bacteria in the environment, already believed to have antidepressant qualities, could increase learning behavior, according to research presented at the 110th General Meeting of the American Society for Microbiology in San Diego.
"Mycobacterium vaccae is a natural soil bacterium which people likely ingest or breath in when they spend time in nature," says Dorothy Matthews of The Sage Colleges in Troy, New York, who conducted the research with her colleague Susan Jenks.
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"We found that mice that were fed live M. vaccae navigated the maze twice as fast and with less demonstrated anxiety behaviors as control mice," says Matthews.
In a second experiment the bacteria were removed from the diet of the experimental mice and they were retested. While the mice ran the maze slower than they did when they were ingesting the bacteria, on average they were still faster than the controls.
Obviously, we don't get in as much soil as our ancestors did.
(In addition, some bacteria in our gut greatly influence brain function [26]. Most native cultures ate fermented foods containing healthy bacteria.)
(4) Exercise [27] boosts intelligence [28] ... and our ancestors got a lot more exercise than we do!
"Even our most highly trained athletes pale in comparison to [29]" farmers 7,000 years ago.
(5) In addition, high levels of cortisol – the chemical released when one is under continuous, unrelenting stress – and poverty can physically impair the brain and people’s ability to learn [30].
Hunter-gatherers had more leisure time [31] - and a more playful attitude [32] - than we do today.
(6) [For this and the next theory, we quote from HuffPost [5].] Dr. Jan te Nijenhuis points to the fact that women of high intelligence tend to have fewer children [33] than do women of lower intelligence. This negative association between I.Q. and fertility [34] has been demonstrated time and again in research over the last century.
(7) "The reduction in human intelligence ... would have begun at the time that genetic selection became more relaxed," Dr. Gerald Crabtree, professor of pathology and developmental biology at Stanford University, told The Huffington Post in an email. "I projected this occurred as our ancestors began to live in more supportive high density societies [35] (cities) and had access to a steady supply of food. Both of these might have resulted from the invention of agriculture, which occurred about 5,000 to 12,000 years ago."
Postscript: Relaxing activities like meditation [36] and prayer [37] have been shown to increase brain mass and connectivity in certain areas of the brain. And sex [38] makes you smarter and causes brain growth.