Recent brain-size decreases in humans as further evidence of the brain/diet connection

Why has brain size decreased 11% in the last 35,000 years and 8% in the last 10,000? Another interesting observation about the brain/diet connection comes from recently updated and more rigorous analysis of changes in brain size in humans over the last 1.8 million years. Ruff, Trinkaus, and Holliday [1997] found that encephalization quotient (EQ) began reaching its peak with the first anatomically modern humans of approximately 90,000 years ago and has since remained fairly constant [see p. 174, Table 1]. Most surprisingly, however, absolute brain size--on the other hand--has decreased by 11% since 35,000 years ago, with most of this decrease (8%) coming in just the last 10,000 years. (The decrease in absolute brain size has been paralleled by roughly similar decreases in body size during the same period, resulting in EQ values that have remained roughly the same as before.)
The significance of constant EQ vs. shrinking brain size in context. This data suggests two points. The first point--relating to EQ--is subject to two possible interpretations, at least on the face of it. One interpretation (characterized by somewhat wishful thinking) might be that, if we disregard the absolute decrease in brain and body size, and focus only on EQ, we can observe that EQ has remained constant over the last 10,000-35,000 years. One could then further conjecture that this implies humans have in some sense been successful in maintaining dietary quality during this time period, even considering the significant dietary changes that came with the advent of the agricultural revolution (roughly the last 10,000 years). However, the problem with such an interpretation is exactly that it depends on disregarding the information that overall body size diminished along with brain size--a most important point which needs to be taken into account.

The alternate, and more plausible and genetically consistent interpretation begins by noting that EQ represents a genetically governed trait determined by our evolutionary heritage. Hence one would not expect EQ itself to have changed materially in just 10,000 years, as it would be unlikely such a brief period of evolutionary time could have been long enough for the actual genetics governing EQ (that is, relative brain size compared to body size) to have changed significantly regardless of dietary or other conditions.

Dietary/physiological mechanism may be responsible. This brings up the second point, which is that the specific question here concerns a slightly different issue: the absolute decrease in brain size rather than the issue of EQ. Since the greatest majority of this decrease took place in just the last 10,000 years , a genetic mutation is no more likely as an explanation for the decrease in absolute brain size than it is for relative brain size, or EQ. This leaves us once again with a physiological/biochemical mechanism as the responsible factor, which of course puts diet squarely into the picture . (Not to mention that it is difficult to imagine plausible evolutionary selective pressures for brain size--primarily cultural/social/behavioral--that could conceivably be responsible for the reversal in brain size, since human cultural evolution has accelerated considerably during this period.)

Far-reaching dietary changes over the last 10,000 years. This leaves us with the indication that there has likely been some kind of recent historical shortfall in some aspect of overall human nutrition--one that presents a limiting factor preventing the body/brain from reaching their complete genetic potential in terms of absolute physical development. The most obvious and far-reaching dietary change during the last 10,000 years has, of course, been the precipitous drop in animal food consumption (from perhaps 50% of diet to 10% in some cases) with the advent of agriculture, accompanied by a large rise in grain consumption--a pattern that persists today. This provides suggestive evidence that the considerable changes in human diet from the previous hunter-gatherer way of life have likely had--and continue to have--substantial consequences.

Brain growth dependent on preformed long-chain fatty acids such as DHA. The most plausible current hypothesis for the biological mechanism(s) responsible for the absolute decrease in brain size is that the shortfall in consumption of animal foods since the late Paleolithic has brought with it a consequent shortfall in consumption of preformed long-chain fatty acids [Eaton and Eaton 1998]. Specifically, for optimal growth, the brain is dependent on the fatty acids DHA (docosahexaenoic acid), DTA (docosatetraenoic acid), and AA (arachidonic acid) during development to support its growth during the formative years, particularly infancy. These are far more plentiful in animal foods than plant.

Eaton et al. [1998] analyze the likely levels of intake of EFAs involved in brain metabolism (DHA, DTA, AA) in prehistoric times, under a wide range of assumptions regarding possible diets and EFA contents. Their model suggests that the levels of EFAs provided in the prehistoric diets was sufficient to support the brain expansion and evolution from prehistoric times to the present, and their analysis also suggests that the current low levels of EFA intake (provided by agricultural diets) may explain the recent smaller human brain size.

Rate of synthesis of DHA from plant-food precursors does not equal amounts available in animal foods. Although the human body will synthesize long-chain fatty acids from precursors in the diet when not directly available, the rates of synthesis generally do not support the levels obtained when they are gotten directly in the diet. This is particularly critical in infancy, as human milk contains preformed DHA and other long-chain essential fatty acids, while plant-food based formulas do not (unless they have been supplemented).

Animal studies indicate that synthesis of DHA from plant-source precursor fatty acids does not equal the levels of DHA observed when those are included in the diet: Anderson et al. [1990] as cited in Farquharson et al. [1992], Anderson and Connor [1994], Woods et al. [1996]. Similar results are reported from studies using human infants as subjects: Carlson et al. [1986], Farquharson et al. [1992], Salem et al. [1996]. For a discussion of the above studies, plus additional studies showing low levels of EFAs in body tissues of vegans, see Key Nutrients vis-a-vis Omnivorous Adaptation and Vegetarianism: Essential Fatty Acids.

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To summarize

The data that human brain size has fallen 11% in the last 35,000 years--with the bulk of that decrease (8%) coming in the last 10,000 years--furnishes, by extension, suggestive, potential corroborative support for the hypotheses explored earlier in this section that increasing brain development earlier in human evolution is correlated positively with the level of animal food in the diet. It also indicates that animal food may be a key component of dietary quality (DQ) that cannot be fully substituted for by increasing other components in the diet in its absence (such as grains).
This indication is important to consider, because evidence available on the changes in food practices of more recent prehistoric humans (and of course, humans today) can be assessed in more depth and with a higher degree of resolution than dietary inferences about earlier humans. In conjunction with data about DHA synthesis in the body vs. obtaining it directly from diet, this provides a potentially important point of comparison for assessing hypotheses about the brain/diet connection.

http://www.beyondveg.com/billings-t...p-anat-4b.shtml

Rambling Road
to Humanity

Anthropologists debunk another
myth of evolutionary progress

Science has, over the centuries, humbled humans, gradually forcing us to abandon the illusion that our species represents the ultimate end of creation. Copernicus and Galileo displaced Earth from the center of the universe; Darwin dashed the conceit that humans originated in a special way, distinct from all other species. Now a group of researchers--Christopher B. Ruff of Johns Hopkins University, Erik Trinkaus of the University of New Mexico and Trenton W. Holliday at the College of William and Mary--throw cold water even on the notion of steady "improvement" within the human line.

In their recent study, Ruff and his colleagues thoroughly analyzed the fossil record to determine the evolving body mass and brain size of the Homo species leading up to us. The results, published in the May 8 issue of Nature, show just how far from the truth is the stereotypical image of a straight progression from small, pea-brained ancestors to the technologically adept egghead Homo sapiens who inhabit the world today. The truth is quite a bit more complicated.

Hominid brains appear to have remained fairly constant in size for a very long stretch from 1.8 million years ago until about 600,000 years ago--a "period of stasis" whose reality has long been debated by scientists. An abrupt break occurred during the Middle Pleistocene epoch (from 600,000 to 150,000 years before the present), when fossils show that the cranial capacity of our ancestors skyrocketed. This trend peaked roughly 75,000 years ago, when archaic Homo sapiens fossils (a category that includes the well-known Neanderthals) indicate a brain mass of about 1,440 grams. Since then, brain mass has actually drifted downward to the 1,300 grams that is typical today.

Brain size alone does not tell the whole story, of course. Intelligence seems to have less to do with brain size per se than with the brain's proportion to the body it must care for and control (and even that link is rather tenuous). Here, too, the results of the Nature paper are telling. Over the nearly two-million-year span that Ruff and his co-authors examined, ancient hominids were on average about 10 percent more massive than modern humans. Body size peaked about 50,000 years ago: Neanderthals were muscular brutes who weighed upwards of a quarter more than modern humans. Since that time, humans have been marching steadily downhill in both stature and cranial capacity (with the exception of some recent gains due to improved nutrition and reduced disease). The good news is that the steeper decline in body mass over the past 50,000 years has raised our ratio of brain to body above Neanderthal levels, even though total brain mass has dipped.

Calculating the size of our progenitors' brains and bodies from a few scattered bones is a tricky process. Many of the bones vary too much from one individual to another to use for such estimation. Teeth wear differently depending on diet, for example. Eye sockets have changed in proportion over the years, and skulls have grown thinner. Past estimates of the body masses of human ancestors have sometimes disagreed by as much as 50 percent. These disparities made it difficult to assess the changing nature of the human line. But in their methodical survey, Ruff, Trinkaus and Holliday found two variables that appear closely tied to body size in even the most ancient humans: the width of the ball joint on the top of the thighbone (which bears much of our weight when we stand) and the breadth of the pelvis. Measuring these dimensions for 163 fossilized hominids, the scientists were able to plot our genus's changes in brain and brawn.

These improved data are already prompting anthropologists to re-evaluate their assessment of the environmental and cultural transformations that shaped human evolution. In an accompanying commentary in Nature, John Kappelman of the University of Texas at Austin offers some intriguing speculations along these lines. The long, dry spell of constant brain size suggests to him that among our ancestors, as in modern apes, competition among males for access to females may have created an evolutionary pressure favoring continued large bodies. Behavior that was "more dependent on brawn than brains," Kappleman writes, evidently was successful enough that there was little evolutionary pressure toward a bigger cranium.

In considering the new reconstructions of Homo over the past 90,000 years, Kappelman is struck less by the roughly constant brain size than by the rapid decrease in body size, which runs quite counter to the earlier steady or upward trends. He suggests that this decrease in overall bulk was favored "by a social structure that relied on more cooperative foraging and better communication skills." At the same time, a better and more reliable food supply could support the metabolic demands of a large brain. "The increase in relative brain size of modern humans may then be, in part, an effect of selection for smaller body mass," Kappelman rather ignominiously concludes.

So this is what it has come to. The favored son of the Garden of Eden has been demoted to the incredible shrinking human.


--Corey S. Powell and W. Wayt Gibbs, staff writers

Original Message:
Posted by: Ken Jacobie (ken~therapist.net )
Date posted: Tue Feb 23 14:04:03 US/Central 1999
Subject: A question about DHA deficiency and the brain...
Message:
You assert that since the Late Paleolithic there has been a cranial capacity reduction. You also suggest that in addition, that there has been a "paralleled decrease" in meat consumption. I would like to know to what period is this reduction in meat consumption is referenced to? Are you sugesting that we(industrialized humans) eat less meat now than in the Late Paleolitc period?


--------------------------------------------------------------------------------
Reply:
Subject: Cranial Reduction
Reply Posted by: David Rawlins (hugeone~rocketmail.com )
Date Posted: Tue Jul 11 12:59:13 US/Central 2000
Message:
Dear Ken, One journal reference for man's recent reduction in cranial capacity is:Nature 387:173-6,1997.As I recall the study our cranial capacity reached its maximum about 35,000 years ago. It has diminished by about 11% since that time.8%of the drop occurred in the last 10,000 years coinciding with the advent of agriculture.Grains rapidly overtook meat in the diet.The decrease in preformed omega-3 fatty acids found in meat is now accelerated in this country where 90%of beef is raised and fattened on grains.The omega-3 fatty acids play a critical role in formation of eicosanoids and in the structure of nerve tissue,particularly brain and retina. Regards DR

http://web2.cast.uark.edu/bin/local.../a/8--3.3.1.1.1

I know this is incredibly old but it was on the first page of a google search I did about comparative brain size. I just wanted to say that the brain size of domestic dogs, cats, and pigs are smaller than their wild counterparts (dogs/wolves, cats/wildcats, pigs/wild boars). I suppose it is possible that our brains have become smaller as we have become more "domesticated" or "civilized". Just something that popped into my own brain while reading tonight.

This is easily demonstrated by logic and a few facts without actually cutting into somebody's brain. The brain runs 30% more efficiently when it runs on ketones. In other words, it does 30% more work for the same fuel, or it does the same work for 30% less fuel. Consequently, eating a ketogenic diet would allow the brain to grow 30% bigger. In fact, it would probably allow the entire body, except fat tissue, to grow significantly bigger. Because if the brain runs 30% more efficiently, the entire body would also run 30% more efficiently.

Remember the Zucker rats Taubes talked about? Their fat tissue remained intact while their lean tissue was shrunk to compensate. Or rather, whatever caused their fat tissue to grow and stay big also caused their lean tissue to shrink and stay small. In this case it was a genetic mutation but isn't it reasonable to assume that this genetic mutation acted exactly on the same mechanisms that dietary carbohydrate act on to achieve basically the same goal?

Biology is for wimps!


One, huge, crazy non sequitur. The laws of thermodynamics and the evolutionary sciences are for wimps!

I'm not someplace where I can dig the article up right away, but I thought I read recently that agriculture has been mostly ruled out as a probable cause of brain size decrease in homo, due to the shrinkage being a) evident prior to the introduction of agriculture, and b) visible in populations that developed agriculture much later. I believe another possibly confounding factor was mentioned as well, but I don't remember what it was.

It was a pretty good article, covering five or six possible theories about why this has occurred.

ETA: It was in Discover magazine, September 2010 issue: “The Incredible Shrinking Brain,” by Kathleen McAuliffe (gated)

In looking for that article by Kathleen, I found one post saying "but i.q. is increasing". I thought that was the most stupid thing anybody said ever. I mean, maybe when we're stupid, anybody less stupid than us looks rather smart. I'd say I.Q. is decreasing in direct proportion to the size of our brain. Or rather, we've grown stupider by about 11% in the last 30,000 years.

Don't confuse intellect with knowledge. The two are not synonymous. We might know a lot more than we did back then but we're not smarter otherwise we'd do something about our shrinking brain, wouldn't we. I mean, if we were smarter we would. But we're not because our brains are smaller therefore we don't do anything about it.

It's like what I've been saying, a priori the brain can't function properly when it's malnourished.

Martin, I'm generally sympathetic to your point of view and appreciate the forcefulness with which you articulate it (seriously, I'm a fan). But in this case I believe either you or the person who wrote the post you're complaining about is conflating IQ with intellect. IQ is a score derived by a test, and it is indeed increasing (see "the Flynn effect"). Whether this means people are getting smarter or not is a matter of great controversy, as is the question of what IQ tests actually measure, if anything besides how well the respondent does on IQ tests. I don't know what post you read that set you off, and maybe the poster did conflate IQ with intelligence. But technically the poster is correct: in aggregate, IQ scores are increasing.

The argument that our brain shrank due to malnutrition is very plausible since we continue to suffer malnutrition due to a grain-heavy diet which we must supplement with various vitamins and minerals to alleviate this malnutrition. This supplementation might just save us from the obvious effects of a grain-heavy diet but now that most US adults are fat, it seems that diet is catching up with us.

And I bet that in spite of a decreasing intellectual capacity, our I.Q. has increased mainly because we do significantly better in the memorization, i.e. trivial part of the I.Q. tests. In other words, we know a lot more than we did but few of us can actually do something with it.

We are stupider. Why? Because we are more numerous. The law of averages and all that. I don't see many examples of genius but I see stupidity everywhere I look and in great number too. Stupidity is allowed to reproduce. Natural selection has been taken out of our nature.

Genius and excellence is now a rarity so much so that we celebrate it. We don't even know how to create a genius and we attribute it to innate talent, i.e. a gift from the divine. Actually that's not entirely true, we know how to create excellence. Take the oldest kid in the class, give him opportunity, give nothing to the rest of the class. We create excellence by suppressing every other kid that is not currently able to perform better than the rest of the class. This means every younger kid or every malnourished kid of the same age. Bear in mind that at 10 years old, a kid that is 11 months older is significantly heavier, stronger, faster, smarter, more agile, more dexterous, etc, than any other younger kid who is also 10 years old. So is that innate ability or is it merely the fact that this kid is older than that kid? The point is that most of us don't know that this is how we differentiate between smart and smarter, i.e. we're not smart enough to figure out the difference between better and older.

If we're not smart enough to determine proper I.Q. because our tests are flawed then the argument of I.Q. increasing has little value, does it.

Yes, yes and yes.

IQ tests, like most other standardized tests, measure a person's ability to think in a A -> B -> C fashion and "catch" errors or puzzles within statements. They don't measure higher level thinking in any meaningful way.


Brain size to social commentary. Interesting tangent, but let's go with it.

Genius, by definition, is a rarity. You could find a race of super-intelligent humans, far more intelligent than "First World" humans, and even they would have standards of genius.

Put a different way, someone isn't an exceptionally fast runner because they run at 10MPH. They are exceptionally fast because everyone else runs at half that pace.


As mentioned earlier, domesticated/tamed animals also have smaller brains. Is the shrinkage due to malnutrition, or is it due to a lack of need for larger brains?

I have absolutely no idea if it has been measured or how it would be measured, but I'd be curious to know if different brain storage mechanisms require different space. IE, wild animals must pass along inherent knowledge of what to eat and when to move. Domesticated animals do not. Should that information be stored in a portion of the brain that takes up more real estate, wouldn't it stand to reason that the brain would shrink as those instincts were discarded? OK...contemplating over. =)

Altari, interesting comparison with domesticated animals. One of the theories outlined in McAuliffe's Discover piece is "selection against aggression," a view promoted by Richard Wrangham:

Wrangham specifically points to the process of animal domestication, and the various phenotypic changes that occur during that process: more gracile features and a smaller cranial cavity, among other things.

To the point of the original post, however -- did agriculture shrink our brains? -- skeptics point out that neither Australians nor southern Africans experienced an agricultural revolution until quite recently, yet their brain size has been declining since the Stone Age as well.

To Martin's theory, minus the agriculture bit, David Geary (a cognitive scientist at the University of Missouri) says:

So maybe you're onto something, Martin (although I think the large group theory may suffer from the same flaws as the agriculture theory -- does it explain universal brain shrinkage?).

On the other hand, University of Wisconsin anthropologist John Hawks thinks our shrinking brains may be a sign that we're getting smarter. Although streamlining the brain probably required some pretty rare mutations, he thinks that as human populations grew (and therefore the gene pool), the chances for such mutations to arise grew as well.

Actually, I didn't say brain size was dependent on intellectual ability. I said the contrary: Intellectual ability was dependent on brain size. If we said brain size depended on intellectual ability (or rather the need or lack of need for it) then we have to also depend on food intake for this brain to grow in the case we need a greater intellect. In other words, the theory works only one way while if brain size depended exclusively on food intake then it works both ways.

If we still say brain size depends on intellectual need, then it stops working because even though we don't need to be as smart, we still have ample food intake to sustain a big brain as the example of a dense population. But the evidence regarding dense populations seems to refute this idea outright for the simple reason that dense populations seem to be sicker than sparser ones. If we're less healthy than sparser populations, then obviously our food intake is to blame. If our food intake is to blame for our health, I doubt it would allow our brain to stay big. Ergo, it's not the fact that our population is dense, rather it's the fact that our food intake in dense populations is inadequate, i.e. we are malnourished. It always comes back to food intake as the primary determinant of brain size.

If we accept this theory:
http://www.proteinpower.com/drmike/...arians-part-ii/

Then we must accept that the shrinkage was due to a lack of adequate nutrition.

I don't know where the idea that our brain started shrinking before we adopted agriculture came from but if I had to guess, I'd say that it was due to some evidence not coinciding with other evidence and the discrepancy would explain it.

When it comes to anthropological evidence, we must assume that a) we don't know everything that can be known and b) not everything that was known can be known. In other words, even if we find everything that we can find, we still don't have the complete picture of a past when we we're there because some actions didn't leave any evidence for us to find. Having said that, the dominant evidence must be the reference for the weaker one. In further words, whatever we're certain of must be our basis for whatever we're not sure of. We're certain that our brain got bigger because we started to eat meat. But we're not certain that our brain got smaller because of some lack of external stimuli because we don't have the evidence of this lack of stimuli. The stronger evidence must rule the weaker one. The most reasonable explanation for our brain shrinkage is that we started to lack what caused, and maintained, our bigger brain.

Furthermore, we have physiological plausibility to explain the above as well, i.e. we know what is in meat that allows our brain to maintain proper function and size.