Our brains are shrinking

The good folks over at superscholar sent me this fascinating infograph, showing how our brains have actually been shrinking over the past 10,000 years. Enjoy.

(click for bigger image)

Given this decreasing brain size doesn’t result in a reduced EQ I suspect the answer may have something to do with the fact that our brains are very expensive, requiring 20% of our daily caloric intake. Any steps evolution can take to reduce the energy used by the brain but still retain the benefits of having a high EQ would be highly beneficial.

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27 thoughts on “Our brains are shrinking

  1. It would be interesting to know how the shrinking is distributed over those 10,000 years. 10,000 years is a long time… Has it been an accelerating shrinking process? Have our brains still been shrinking the last say 1000 years, and are they still shrinking now? If not, why is the shrinking characterised as “at an alarming rate”?

    Also, have brains shrinked evenly across different populations all over the world?

    The efficiency/calories argument may apply to primitive agricultural societies but doesn’t sound that relevant for modern humans in the developed world where most people struggle to keep their calories intake down rather than keep up with the brain’s use of calories.

    • One study described it as smooth but inversely exponential, suggesting it is broadly the same from year to year but the rate has been gradually decreasing. As such I probably wouldn’t describe the trend as alarming.

      Even in a high calorie environment reducing brain size can be beneficial, because it means even more calories can be spent in other areas.

    • Thank you for your reply.

      Even in a high calorie environment reducing brain size can be beneficial, because it means even more calories can be spent in other areas.

      I suppose those other areas would have to be a competitive advantage for passing on one’s genes (more competitive than a large brain), so I suppose that everyday no-brain activities like watching TV and checking Facebook updates wouldn’t count:-) but for example be better at work and earning more money would, assuming the benefits of that would provide a better chance of raising kids…

      I think I may be leaning most towards the “Social support” argument.

    • Areas which benefit from having additional calories invested in them are typically related to childbirth and growth. More calories means healthier pregnancies, and a shorter inter-birth interval. The kids themselves also generally grow and mature faster.

      The fact we’re no longer pooping out as many kids as we can does mean these benefits aren’t as significant as they once were. However, even in modern society the effects are still noticeable and useful, so it would still be beneficial to reduce brain size if possible.

  2. “Any steps evolution can take to reduce the energy used by the brain but still retain the benefits of having a high EQ would be highly beneficial.”

    I agree, but how do you suppose such a traits would give an individual a reproductive advantage?

    • Being able to invest calories in other areas of the body generally results in improvements in growth and reproduction. Higher caloric intake (up to a point, obviously) result in faster maturation of infants and a shorter “recovery period” between births, for example. Continuing to be able to invest calories in these areas without over-eating would perhaps see increased benefits.

      Although these traits wouldn’t confer as much of an advantage as they once did, they still significantly increased reproductive success of Western humans as late as the 18th/19th centuries and possibly continue to do so to this day.

  3. Pingback: Sir David Attenborough is wrong, humans are still evolving | EvoAnth

  4. In a harsh environment, quality offspring is favored over quantity.

    In an abundant environment, the reverse is true.

    Society has created an environment of artificial abundance that favors dysgenics as genes seek to capture market share at the expense of quality or sustainability like the old .com bubble companies of the 90s.

    • Well it depends on where you are talking about. If this is really related with agriculture, then the results should be strongly dependent on the location. I seem to remember that Natufian developed the very first agriculture around 11000 BC, perhaps following changes in their immediate environment due to the Younger Dryas event. In the same time, agriculture arrived in Denmark only around 4000 BC. That’s a big difference ! Do Danes have larger brains than people of Levant ?

      • From what I gather the Natufians were still mostly hunter-gatherers. There may have been a bit of domestication, but then modern h/gs also often plant a few resources to supplement their diet. Populations completely reliant on farming didn’t emerge until a bit later, around 10,300 BC

        Your idea of looking at recent uptake farmers is a good one.

      • Yes, it would be interesting to compare cultures like Europeans that copied agriculture only ‘recently’, versus the areas where it originated (Africa, Middle East, and Asia; independently, as far as I understand). The more decisive test, however, would be to look at current h/g societies. I wouldn’t be surprised if that has been done already. Does anybody know of any data?

        • I’m not aware of any research on the subject; and a quick search doesn’t turn up any related results. Anyone know where we can get our hands on some hunter-gatherer brains?

          That said, given that many modern h/gs groups have been influenced by agrarian societies to quite a large degree I think a better test would be to look at historical remains rather than modern ones.

          • I spotted this on the wiki article about Bushmen: “Ashley Montagu noted that Bushmen have the following neotenous (childlike) traits compared to Caucasoids: large brain, [….]” and the reference for this statement is “Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.” I don’t have access to it, but if true, then it somehow could corroborate the link between shrinking brains and agriculture.

            • I can get a bit of the book through google books and it does certainly seem to say that. However, I can’t see the actual figures or source material so am unwilling to give it that much credence. Unfortunately my university library doesn’t seem to have a copy of it either.

    • The first farmers had a really bad diet, having only figured out how to domesticate a handful of animals. Maybe their poor diet made a large brain a deleterious trait that was selected against, a pressure that is easing off now our diets are better. Hence why the rate of shrinkage is decreasing.

      Also, got a tonne of views from your redditing. Thanks for that

      • I didn’t know that farmers had a bad diet compared to h/gs. The decrease in brain size would then be consistent with the expensive tissue hypothesis. However, that can’t be the only factor, since we have a better diet now than h/gs, and presumably have for hundreds of years. If expensive tissue hypothesis was the only reason then the trend would have reversed (instead of just slowed).

        • Indeed, human height also decreased during this period (as the infographic shows), which is what you would expect from a poor diet. However, within the last 1,000 years stature has begun increasing again as our diets are now tippy top. Brain size shows no evidence of such a recent increase (although the decrease is slowing). It was also decreasing much more than would be expected based on the reduced body size, so this can’t be explained away as allometry either.

          • I thought EQ (I had actually thought you meant emotional quotient before, talk about inattentive) was suppose to account for allometry. If our brains are still getting smaller, but in the last 1000 years are bodies are getting bigger then how is this consistent with constant EQ? I don’t get it. If that part of the graphic is wrong then can the decrease in shrink rate be accounted for just by an upward pressure from bigger body? I.e. the other selective pressure against big brains is still the same as 10k years ago, but our bodies getting bigger is counteracting the pressure partially to result in slowed rate.

          • Like I said, I think most claims of EQ stability are based on comparisons of present day human with much older samples. If it continued to increase after the first measurements, then decreased recently then it may give the appearance it has remained stable over this time.

            Changes in brain size are greater than would be expected based on allometry.

  5. Pingback: Our brain is shrinking but our frontal lobe is growing | EvoAnth

  6. The mention that we are getting more and more docile, social and peacefull over the years gives me hopes that we will continue to prosper a a species and avoid self-destruction

  7. Pingback: His do fat people mentally function? - Page 5 | Mark's Daily Apple Health and Fitness Forum page 5

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