Are We Becoming Less Intelligent?

A portrait of Eratosthenes, who lived from 276 BC to 194 BC (public domain image)

Somewhere around 200 BC, a man named Eratosthenes learned that at noon on the Summer Solstice in Syene, a man looking down a deep well would see no light in the well, because his shadow would block all the sunlight. He reasoned that this meant the sun was directly overhead in the city of Syene at that moment. Well, he lived in Alexandria, which was about 500 miles south of Syene. He measured the length of a pole’s shadow in Alexandria at noon on the Summer Solstice and from that determined the angle at which the sun shined on Alexandria when the sun was directly overhead in the city of Syene.

Why would Eratosthenes do this? Well, like all ancient natural philosophers (including the Christian ones who would come a few hundred years later), he understood that the earth is a sphere. If you are under the mistaken impression that most ancient people thought the earth was flat, you need to realize that this is a textbook myth that is repeated over and over again but is nevertheless quite false. Since he knew that the earth is a sphere, he used his measurement to reason that the distance between Syene and Alexandria is about one-fiftieth of the distance around that sphere. He then took the known distance between Syene and Alexandria and multiplied by 50 to get the total distance around the earth. The unit he used to measure distance (the stadium) had different definitions at the time, but assuming he used the one that was typically used for long journeys, his measurement was correct to within 2% of today’s accepted value.1

Does that surprise you? It shouldn’t. In today’s culture, we think of ancient people as ignorant savages, but in fact, many of them were incredibly intelligent. According to at least one geneticist, they were probably more intelligent than we are! In a two-part series published in the journal Trends in Genetics, Dr. Gerald R. Crabtree states:2

I would wager that if an average citizen from Athens of 1000 BC 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.

How can Dr. Crabtree make such a seemingly absurd statement? He argues that our intellectual abilities are governed by all sorts of genes. In fact, based on some studies that have been done on X chromosome mutations that lead to intellectual deficiencies, he produces a conservative estimate that human intelligence is influenced by 2,000-5,000 genes. Based on estimates of mutation rates in the human population, he suggests that this collection of genes must have been affected by many mutations over the past three thousand years. Indeed, he suggests:

…it is very likely that within 3000 years  (120 generations) we have all sustained two or more mutations harmful to our intellectual or emotional stability.

In his estimation, then, harmful mutations have collected over the years, reducing our intellectual ability. But why hasn’t natural selection weeded them out? He answers that in the second part of his two-part series.3 He suggests that once we started living in high-density societies, catching diseases from other people was much more likely to cause someone to die than were intellectual deficiencies. As a result, natural selection worked mostly on the genes that govern our immune systems, not on the genes that governed our intellectual abilities. In addition, societies tend to make people who are intellectually deficient more survivable, because a society can “find a place” for those who would probably die on their own. This sheltered people from the effects of natural selection when it came to intellectual deficiencies. As a result, natural selection could not get rid of the mutations related to intelligence; thus, people simply aren’t as intelligent now as they were 3,000 years ago.

While the good doctor’s proposal is an interesting one, I am not sure he makes his case. Indeed, in the same journal, another geneticist (Dr. Kevin J. Mitchell) argues against his position, pointing out studies that seem to indicate that intelligence-related genes are not sustaining a high mutation load. He also argues that the complex social interactions used in societies actually produce increased intelligence in future generations.4 As he concludes:

Thus, despite ready counter-examples from nightly newscasts, there is no scientific reason to think that we humans are on an inevitable genetic trajectory towards idiocy.

I honestly don’t know who has the better arguments here. I do think that Adam and Eve had mutation-free genomes, which would tend to imply that everything about them was better than we are today. At the same time, however, the Creator has designed our genomes to be adaptive, allowing the human population to change over time to meet our changing needs. As a result, even if we are carrying around some mutations in our intelligence-related genes, it’s not clear that we are significantly less intelligent than our ancient ancestors.

I do hope that more research is done on this question, because I find it incredibly interesting. If nothing else, I hope it helps to dispel the absurd notion that ancient people were intellectually inferior to us!


1. Kelly Trumble, The Library of Alexandria, Clarion books 2003, p. 24
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2. Gerald R. Crabtree, “Our fragile intellect. Part I,” Trends in Genetics, 2013, http://dx.doi:10.1016/j.tig.2012.10.002
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3. Gerald R. Crabtree, “Our fragile intellect. Part II,” Trends in Genetics, 2013, http://dx.doi:10.1016/j.tig.2012.10.003
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4. Kevin J. Mitchell, “Genetic entropy and the human intellect,” Trends in Genetics, 2013, http://dx.doi:10.1016/j.tig.2012.11.010
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  1. Nathanael says:

    My mom and my sister both say that most people thought the earth was flat and only a few thought that the earth was round. My mom says sailors were afraid of falling off the edge of the world. She wants you to show evidence that most ancient people thought the earth was round.

    1. jlwile says:

      Nathanael, I am afraid that your mother and your sister are simply wrong. They have been fooled by a very popular textbook myth. Sailors have always known the earth is a sphere, because they saw that when they were standing on shore, they could see a departing ship longer if they were at a higher elevation. That told them the sea was curved, because the earth was a sphere. Your mom and your sister have probably been taken in by the myth that Columbus had trouble getting support for his voyage because people thought the earth was flat and that a ship would sail off the edge of the earth. As Jeffrey Burton Russell Russell says in his classic book, Inventing the Flat Earth: Columbus and Modern Historians:

      “The myth that people thought Columbus would sail off the edge of the earth was popularized by Washington Irving (1783-1859). According to respected Columbus biographer Samuel Eliot Morison, Irving’s version the story is ‘pure moonshine. Washington Irving, scenting his opportunity for a picturesque and moving scene,’ created a fictitious account of this ‘nonexistent university council’ and ‘let his imagination go completely…the whole story is misleading and mischievous nonsense.’ – [Jeffrey Burton Russell, Inventing the Flat Earth: Columbus and Modern Historians, Praeger Pub 1991, p. 53]

      The reason Columbus had difficulty financing his journey was because people knew the circumference of the spherical earth, and no one thought a ship could sail that far without running out of supplies.

      All the ancient Greeks from Pythagoras (c. 500 BC) on wrote about the earth being a sphere, and the ancient Christians agreed. Basil of Caesarea (c. 330-379) wrote that the earth is a sphere that is nested inside the heavenly sphere. Other ancient Christian philosophers, like John Philoponus (490-570) agreed.

  2. josiah says:

    This would seem to ignore any possible influences on intelligence from upbringing. People can learn to think, or they can learn to simply accept their lot or repeat the views of authority figures. A society where intellectual abilities are valued (and monetarily rewarded) should tend to raise more people who learn to question.
    I would expect that even if our genetic raw materials were lower quality, people would be more intelligent now on average having had more mental stimulation and more encouragement to contemplate things. I’d also point out that the average Athenian was far too busy to be calculating the size of the Earth, and these people we read about are the philosophical elite.

    The defence rests, the prosecution invites witness “Reality TV” to the stand…

    1. jlwile says:

      You are quite correct, Josiah. He is ignoring nurture and concentrating only on nature. There is a reason for this. Nurture can overcome nature, but only for a single generation. Ignoring the possibility of epigenetics, you can’t inherit nurture. Thus, in determining how intelligence varies from generation to generation, nurture is not an important factor, at least not as we understand things right now. Of course, as we learn more about epigenetics, that might change. But right now, to track how intelligence changes from generation to generation, genes are the best measure we have.

      You are also quite correct that the people we read about in ancient times are the philosophical elite. They may very well not represent the average Athenian. This is why the genetic argument is important.

      Your last sentence illustrates once again why I look forward to your comments!

  3. JBowling says:

    Just found your site. Very cool. Keep up the good work. By the way Stephen J. Gould wrote a paper on the flat-earth myth too. Also, Augustine in his City of God mentions the earth being a sphere. He doubts that people live on the other side of the earth, but doesn’t seem to doubt its sphericity per se.