Intelligence Research
New peer-reviewed findings on how reasoning, memory and general ability actually work — reported with the sample size and the error bars.
What Is the Smartest Land Animal? What Studies Measured
No test ranks every land animal. On one self-control test, chimpanzees scored 100% and coyotes 95.0%; the elephant that passes a mirror test had the lowest score on another. Here is what each study measured, and what it did not.
What Is the Smartest Fish in the World? What Lab Studies Show
No study ranks fish species on one task. The famous results rest on 4 marked wrasse, 14 groupers and 8 goldfish, and the goldfish study measured a feeding time that came once in 24 hours, not a 3-second memory.
Who Is the Smartest Person Living? Why No One Holds the Title
No one can be named the smartest person living: no test reports scores above about 160, most people have never been tested, and Guinness World Records ended its "Highest IQ" category in 1990 because it judged IQ tests too unreliable to pick one record holder.
Who Is the Smartest Woman in the World? What Is on Record
The only woman Guinness World Records ever listed under "Highest IQ" was Marilyn vos Savant, with 228 on an old ratio scale and 186 on a high-range test. The two numbers are not comparable, and Guinness retired the category in 1990.
What Is the Smartest Reptile? What Lab Studies Actually Show
No study we found ranks reptile species on one set of tasks, and reptiles have no IQ. The best-documented results are small: four of four red-footed tortoises solved a detour task after watching another tortoise, and none of four that did not watch solved it.
Who Is the World's Smartest Mathematician Alive? Prizes Show, IQ Cannot
None of the living mathematicians people search for has a published adult IQ score, so we ranked them by what can be checked: five top prize lists. One holds four of the five, and 13 hold three. Terence Tao holds two, Edward Witten one and Grigori Perelman none.
What Is the Smartest Insect? What Bees, Ants and Flies Can Do
No study ranks insects on one test, but the honeybee has the strongest evidence: it counts up to four landmarks, places zero below one and adds or subtracts one. Its brain holds under a million cells, and a fruit fly's holds 139,255 neurons.
Smartest Bird in the World: Ranked by What Studies Measured
Counting neurons in 28 bird species puts the blue-and-yellow macaw first, with 2.46 billion in the forebrain, and the raven fourth. On behaviour tests, ravens, crows, rooks, jays and grey parrots all have standout results. No study ranks them on one test.
Einstein's Brain: Taken, Weighed, Sliced and What It Did Not Show
Einstein's brain weighed 1,230 grams, about average for a man of 76. It was cut into 240 blocks that are now spread across three institutions, and the studies of it are more modest, and more disputed, than the headlines.
Does Aphantasia Affect IQ? What the Studies Measured
No study has measured IQ in a representative sample of people with aphantasia, the lifelong absence of mental pictures. The two small studies that report IQ-style scores disagree on direction, +5.5 and -4.0 points, and neither gap was significant.
Gen Z IQ: Is Gen Z Less Intelligent Than Its Parents? What the Data Show
A neuroscientist told the US Senate in January 2026 that Gen Z is the first generation to underperform its parents, "even general IQ". The written testimony does not say it, and the best IQ data stop with people born in 1991.
Do High-Scoring Children at Age 7 Stay High? What 11,119 Children Show
In a study that followed children from age 4 to 21, only 16% of those scoring above 115 at age 7 were still above it at 16. Test-to-test correlations of .32 to .65 explain why an early high score is a snapshot, not a verdict.
Average Reaction Time by Age (in Milliseconds) and What It Says About IQ
A typical simple reaction time is roughly 215 to 240 milliseconds in a calibrated lab and 273 ms on Human Benchmark's online test. Age adds about 0.55 ms a year, and the link to IQ is about -.3.
Does IQ Above 120 Stop Mattering? What a 50-Year Study Found
The "threshold hypothesis" holds that intelligence stops predicting achievement past roughly 120. A 50-year study tracking thousands of gifted 13-year-olds into midlife found the opposite: finer differences within the top 1% still predict who earns a doctorate, a patent or tenure.
Childhood Adversity and Cognition: What a PNAS Study Found
A September 2026 PNAS study scanned people aged 0 to 21 and linked stressful life events to one brain circuit and cognition to another. The effects are small, and one did not replicate.
An MRI Map of the Gifted Brain: What the Scans Show
A 2021 imaging study compared children with IQ scores above 145 to typically developing peers and found specific, named memory structures that were measurably different. Here is what the scan actually found, and what it does not prove.
Would People Screen Embryos for Low IQ? A New Study Answers
A survey of nearly 1,500 Americans found people say IQ screening is less acceptable than disease screening — then, given real genetic risk scores, avoid a high-risk-for-low-IQ embryo almost as often as a high-risk-for-heart-disease one.
Hitler's IQ Was Never Tested: The Nuremberg IQ Scores of 21 Nazi Defendants
Before the main Nuremberg trial opened in November 1945, the prison psychologist gave 21 of the defendants an IQ test. Their scores ran from 106 to 143 and averaged 128. Adolf Hitler, dead since April 1945, was never tested, and any IQ you see quoted for him is invented.
CHC Theory: The Model Behind Every Modern IQ Test Score
A full-scale IQ is not one thing a test measures directly. It is a composite built from several index scores, and the theory that decides which ones is called Cattell-Horn-Carroll — CHC for short.
Spearman's Law of Diminishing Returns: Does g Weaken at High Ability?
Cognitive tests correlate less strongly with each other among high scorers than among low scorers. If that holds, a single full-scale figure carries less information the higher it goes — and the evidence for it is real but smaller and shakier than the idea's popularity suggests.
Savant Syndrome and IQ Tests: Why a Single Score Can Miss an Extraordinary Ability
Savant syndrome pairs an ordinary or low Full-Scale IQ with one narrow ability that is exceptional, and it is the clearest case for why the index profile matters more than the total.
Brain Size and IQ: What a Correlation of 0.24 Means
The largest synthesis of the question pooled 88 imaging studies and put the association between brain volume and IQ at roughly 0.24. That is about six per cent of the variation in scores, which is enough to rule out the strong claim and the flat denial at the same time.
What Is the g Factor in Intelligence? Definition, Example and Test
Scores on tests that look nothing alike still correlate positively. g is the factor pulled out of that pattern: about 40 per cent of the variance in a diverse battery, which makes a single summary number defensible and also far less than the whole story.
A Century of Rising IQ Scores Has Stalled in Wealthy Countries
Average scores climbed for decades, then flattened and in places slipped. None of it shows on a score report, because every test is reset so the average is 100 again — which is why a 1990 score is not a 2026 score.
Working Memory and Reasoning Are Closely Related. They Are Not the Same Thing
The correlation between them is one of the sturdier findings in cognitive psychology. How strong it is, and what it implies about training either one, is where the agreement stops.
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