Modern Humans’ brain size has shrunk by 20%
Collaborations,  Press Release

Modern Humans’ Brain Size Has Shrunk By 20%

Modern humans’ brain size has shrunk by 20%. Hello everyone, I hope you are well. In today’s post, I will be sharing a press release on research that shows modern humans’ brain size has shrunk by 20%. Are we dumbing down? Both brain size and IQ are falling in modern humans, coinciding with a significant increase in mental illness. What we eat is to blame, says Professor Michael Crawford, author of the new book ‘The Shrinking Brain’. Sir David Attenborough is convinced he is right. IQ scores have also been steadily falling for the past few decades.

Modern Humans’ Brain Size Has Shrunk By 20%

Norwegian researchers, headed by Ole Rogeberg, a senior research fellow at the Ragnar Frisch Centre for Economic Research in Norway, analysed the IQ scores of Norwegian men born between 1962 and 1991 and found that scores steadily decreased among those born after 1975.[1] “Similar studies in Denmark, Britain, France, the Netherlands, Finland, and Estonia have demonstrated a similar downward trend in IQ scores,” says Rogeberg. “The decline is due to environmental factors,”

This coincides with a change in the Western diet away from fat and towards carbohydrates and sugar, based on the mistaken belief that it was fat, not sugar, that was causing heart disease and that we should all eat a low-fat diet. Since then, our IQ scores have dropped by about 7 per cent per generation.

“We are heading for an idiocracy”, says Professor Crawford, Director of the Institute of Brain Chemistry and Human Nutrition. Currently, one in five of the world’s children and adolescents have a mental health condition.’ [2]  If this trend continues, by 2080, he predicts that more than a third of the world’s population will be borderline mentally retarded.

The World Health Organisation report says ‘there has been a 13% rise in mental health conditions. One in eight people now has a mental illness. The incidence of depression is through the roof. Last year in the UK, there were over 100 million prescriptions for antidepressants.

Crawford is convinced it is the modern-day diet that is causing us to dumb down. “Our genome is adapted to eating the wild foods we ate during our species’ evolution. Today’s diet bears no resemblance to this.”

The Shrinking Brain

In his book, The Shrinking Brain, he says, “Our ancestors evolved a unique 1,600-cc brain from our ancestral 350-cc brain of the chimpanzee, despite our genome only differing by 1.5%.[3] This could only have happened by providing brain-specific building nutrients from land and sea. There is incontrovertible evidence of early Homo sapiens exploiting the marine food web in coastal Africa.” In other words, we were the waterside apes who became smart, with bigger brains, by eating mussels, oysters, crabs, and fish.

Professor Crawford discovered in 1971 that the brains of all mammals are rich in omega-3 DHA. The size of their brain varied according to their dietary supply of DHA found in seafood. A dolphin, for example, has a 1,700-cc brain, slightly larger than ours, while a lion has a 320-cc brain, about that of a chimpanzee. “The mix of wildland and aquatic foods is powered by the encephalisation of the brain from the 340 cc of the chimp to the 1,500–1,700 of the cro-magnon. DHA is not only involved in signalling, but it stimulates gene expression in the brain, so the rich aquatic food sources constantly, every day, would have powered the increase in brain size and function,” says Crawford.

“Today’s diet contains less than a tenth of the omega-3 fats that our ancestors ate, which has dire consequences for mental health. Increased rates of depression, autism, ADHD, and dementia are all strongly linked to a lack of seafood. Increased intake from eating fish or supplementing omega-3 fish oils reduce dementia risk by 20 percent. [4] While a plant-based diet has many benefits, those who eat no fish are especially vulnerable and must supplement omega-3 DHA, derived from algae. The only way to be sure you have enough is to get a blood test to test your levels specifically.” Patrick Holford, CEO of the charity,

Do It At Home’ Pin-Prick Test

The charity has just launched a simple ‘do it at home’ pin-prick test that can give you a clear indication of your Omega-3 levels, alongside a cognitive function test that can help identify what’s driving future risk and show you how to dementia-proof your diet and lifestyle.

Canadian neuroscientist and brain expert Professor Stephen Cunnane at the University of Sherbrook in Canada agrees: “A shore-based diet, i.e., fish, molluscs, crustaceans, frogs, bird’s eggs and aquatic plants, provides the richest known dietary sources of brain-selective nutrients,” says Cunnane. “Change in diet away from marine foods is the likely explanation for this decrease in brain size.”

Sir David Attenborough, a supporter of the waterside ape theory, agrees: “Gathering molluscs is far easier than chasing elephants and wildebeests across the savannah.”

Today, under 5 per cent of children achieve the essential requirement for omega-3 from seafood.[5]

Professor Michael Crawford, who is a visiting professor at Imperial College’s Chelsea & Westminster campus and science advisor to the charity, was part of the team that has recently established that if a pregnant woman lacks omega-3 DHA, she produces a substitute fat, oleic acid, to fill the baby’s brain. But it doesn’t work. Levels of oleic acid in a pregnant woman’s blood predict preterm birth, which carries the highest risk of developmental brain problems and mental deficits in their offspring, as well as a risk of learning and cognitive disabilities. Low omega-3 and B vitamins in mothers increase the risk of lower IQ, learning, and emotional problems in children [6].


Anyone concerned about their levels of Omega-3 can now test their levels with a home test kit provided by the charity, which is offered alongside a free cognitive function test that assesses how well your diet supports your brain health. A new study shows that the higher the omega-3 index and DHA, which is what Food for the Brain measures, the greater the brain size and cognition of older people.[7] Brain size predicts cognitive abilities.

Brain size is calculated from skull capacity. Homo sapiens skulls dating back to 29,000 years ago had a brain capacity of 1,660 cc. By 10,000 years ago, it was around 1,500 cm or 1.5 kilogrammes. The average brain size today is a fifth smaller, at 1,336 cc. Brain size may have shrunk from 10,000 years ago, coinciding with humanity developing more land-based agriculture and eating less marine food along rivers and coasts.

“We are inviting people to join our ‘citizen science’ study to track the impact of diet and Omega-3 on cognitive function over time,” says the charity’s CEO, Patrick Holford, a brain health expert. “I’m convinced we are digging our graves with a knife and fork, and our brains and mental health are suffering as a result. Alzheimer’s, which is preventable, is also a direct consequence.”

I hope you enjoyed that.

Talk soon.


The Food for the Brain Foundation ( is an educational and research charity on dementia prevention. It’s a free online validated Cognitive Function Test, followed by the Dementia Risk Index questionnaire assessing eight drivers of dementia, including ‘brain fats’ and ‘low carbs & GL’, thus identifying those eating too many carbs and not enough brain fats, then advising them what to do.

Supporting Research


Bratsberg B, Rogeberg O. Flynn effect and its reversal are both environmentally caused. Proc Natl Acad Sci U S A. 2018 Jun 26;115(26):6674-6678. doi: 10.1073/pnas.1718793115. Epub 2018 Jun 11. PMID: 29891660; PMCID: PMC6042097.


Cunnane SC, Crawford MA. Energetic and nutritional constraints on infant brain development: implications for brain expansion during human evolution. J Hum Evol. 2014 Dec;77:88-98. doi: 10.1016/j.jhevol.2014.05.001. Epub 2014 Jun 11. PMID: 24928072.



Montgomery P, Burton JR, Sewell RP, Spreckelsen TF, Richardson AJ. Low blood long chain omega-3 fatty acids in UK children have associated with poor cognitive performance and behaviour: a cross-sectional analysis from the DOLAB study. PLoS One. 2013 Jun 24;8(6):e66697. Doi: 10.1371/journal.pone.0066697.


Wei BZ, Li L, Dong CW, Tan CC; Alzheimer’s Disease Neuroimaging Initiative; Xu W. The Relationship of Omega-3 Fatty Acids with Dementia and Cognitive Decline: Evidence from Prospective Cohort Studies of Supplementation, Dietary Intake, and Blood Markers. Am J Clin Nutr. 2023 Jun;117(6):1096-1109. doi: 10.1016/j.ajcnut.2023.04.001. Epub 2023 Apr 5. PMID: 37028557; PMCID: PMC10447496.


Loong, S.; Barnes, S.; Gatto, N.M.; Chowdhury, S.; Lee, G.J. Omega-3 Fatty Acids, Cognition, and Brain Volume in Older Adults. Brain Sci.2023,13,1278. 10.3390/brainsci13091278

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  • Barbie Ritzman

    Interesting, to say the least. I’m happy to learn that Omega-3 levels can now be tested at home with a kit. Thanks for sharing the link; I will check it out now.

  • Marysa

    That is crazy that brain size is shrinking. If anything, I thought it would be growing. I am surprised! But it makes sense without having a healthy and nutrient dense diet. I will have to work on better omega supplements.

  • Jen Schreiner

    YES!!!! I have been reading on this subject for the last six months. I actually have changed my diet to an animal-based one. At first, I did it because my doctor made the suggestion based on my digestive issues. My doc also follows animal-based eating like our ancestors. I feel the fantastic. My digestive problems are gone, my energy is up and I have lost some weight to boot. If everyone could get away with processed foods and take it back to ancestors’ way of eating, so many problems would be gone.

  • Luna S

    Interesting article & research topic. I can definitely see how all of the processed foods we eat, the chemicals and more that we are affected by could start causing changes like that.

  • Stephanie

    Such an interesting read on this study of our brain sizes and why we are heading in this direction. I need to start eating not only for my body – but also my brain.

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