4 Apr 2024

Scientists find the human brain has grown by whopping 7% since 1930... but there are signs IQs have gone backwards in recent years

This is an interesting paradox. There is a long-standing correlation of about 0.3 between brain size and IQ.  So the findings are weakly contradictory. I think, however, that I may be able to give an outline of a solution to that  puzzle.

I once hypthesized that better  perinatal practices were reponsible for the average IQ gains that were observed in many countries during the 20th century

http://jonjayray.com/iqgain.html

If my hypothesis is correct, the benefit of improved obstetric practice should level out once best delivery procedures became  normal.  And it was so.  The  growth in IQ scores did level out towards the end of the 20th century.

But we need to ask the old legal question "cui bono?".  Which babies did  it help most?    Babies who were physically normal would be helped to survive with undamaged brains so brain damage due to delivery practices should be rare and hence lead to a rise in average IQ.

And the correlation between higher IQ and larger brains means that less pressure on the head during delivery (due to episiotomy, Caesarians, principally) would be particulary helpful to undamaged survival among individuals with big heads.  So a major source of better and undamaged survival among high IQ individuals would be the safer delivery of big headed babies

But what about babies which had some congenital problem that only modern medicine saved from oblivion?  In many cases the congenital problem would have affected the brain and Left us with an individual of lower IQ, much lower in some cases

So we have two populations with opposite effects from modernity.  "Normals" who avoided damage so became brighter on average and another which survived against the odds and which was on the average of lower IQ.  So what we find reported below is the averaging out of those two populations

A note of caution, however. It is much easier and more accurate to measure head size than it is to measure IQ, and the IQ gain reported is quite low and of no certain reliabiity.  And in general the higher you go up the IQ scale the lower is the reliability of the differences.  So much more segmentaion of the populations concerned would be needed to give any certainty about what is going on

Gen Z and Alpha may have a larger brain than people who were born 100 years ago, yet studies have indicated they also have the lowest IQs of previous generations.

Researchers at the University of California (UC) Davis Health studied different brain sizes of people born from the 1930 through 1970s, finding a 6.6 percent increased in brains among Gen X compared to the Silent Generation.

The team theorized that growth could be caused by external influences like health, social, cultural and educational outside factors and could reduce the risk of age-related dementia.

It comes as more recent studies have indicated that even younger generations' IQ scores have dropped in recent decades, which researchers have linked to an overreliance on phones and the internet.

Brain size doesn't necessarily make people more intelligent, and research has suggested that their is only a slight relationship between the two.

Neuroscientists have found that extra brain mass actually accomplishes very little when it comes to intelligence, and instead it serves to allow people to store more lifetime memories, according to Psychology Today.

However, the latest findings could be a contributing factor to why younger generations have a lower risk for developing dementia or Alzheimer's.

The new study was conducted across 75 years and found the brain consistently grew by 6.6 percent for people in the 1970s compared to those born in the 1930s.

Today's generation's brains measure about 1,400 milliliters in volume, but the average brain volume for people born in the 1930s was 1,234 milliliters. 

The researchers reported that factors like greater educational achievements and better management of medical issues might explain why people's brains have grown over the decades.

'The decade someone is born appears to impact brain size and potentially long-term brain health,' said Charles DeCarli, first author of the study and professor of neurology at the UC Davis Alzheimer's Disease Research Center.

Researchers looked at patterns of cardiovascular and other diseases of people born in the 1930s and introduced MRI tests (brain magnetic resonance imaging) of people of the second and third generations of the original 5,200 participants.

The MRIs were conducted between 1999 and 2019 on people born in the 1930s through the 1970s, consisting of more than 3,000 participants with an average age of 57 years old.

The area of the brain that grew the largest was the cortical surface area which controls motor activities and sensory information.

 Scientists have uncovered hundreds of different and unique regions of the brain

They reported that the area increased by 15 percent in volume and the region of the brain involved in learning and memory, called the hippocampus, had also increased in size.

However, the number of people struck by Alzheimer's has decreased by 20 percent since the 1970s, according to a separate study, and researchers are now saying increased brain size may be the culprit.

'Larger brain structures like those observed in our study may reflect improved brain development and improved brain health,' DeCarli said.

'A larger brain structure represents a larger brain reserve and may buffer the late-life effects of age-related brain diseases like Alzheimer's and related dementias.'

The brain growth in younger generations could increase brain connectivity, the study said, which could lead to more accurate and efficient performances on tasks.

Yet, even as researchers report the brain is growing with each generation, Gen Z and Alpha's IQs have dropped by at least two points, according to studies in Finland, France, the UK and other countries.

A 2023 study reported that IQ scores in the US have also dropped, but did not specify the exact drop, adding that the decrease could be due to disruptions to in-person learning during the Covid-19 pandemic.

The researchers also said the rise in social media use could be at fault, as skills like verbal reasoning, visual problem solving and numerical series tests have all gone down.

Academic and science presenter professor Jim Al-Khalili previously told Dailymail.com in 2022 that despite our ‘vastly increased scientific knowledge… the human brain hasn’t got bigger or more efficient or better than it was thousands of years ago.'

This is in direct contrast to the newest findings that the human brain is getting larger, but also raises the question of how cognitive development is increasing while gen Z and Alpha struggle to meet the same IQ levels as past generations.

https://www.dailymail.co.uk/sciencetech/article-13244559/Gen-Z-Alpha-larger-brains-IQs-decreasing.html

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