Stuart Ritchie’s “Intelligence”: Book Review, Notes + Analysis

Poor Ash’s Almanack > Book Reviews > Science + Engineering + Math > Psychology

Overall Rating: ★★★★★ (5/7) (solid for its category)

Learning Potential / Utility: ★★★★★ (5/7)

Readability: ★★★★★★★ (7/7)

Challenge Level: 1/5 (None) | 114 pages ex-notes (160 official)

Blurb/Description: Cognitive researcher Stuart Ritchie provides a brief but important, thoughtful, and balanced summary of a century of research on intelligence.

Summary: I came to this book in an unusual way: after reading Siddartha Mukherjee’s The Gene, which alternates between revelatory, wonderful science writing and vaguely-social-justicey incoherence, I was reviewing the actual science on intelligence, which Mukherjee presents in a very biased, narrow, and ultimately misleading way.  In the process, I stumbled upon Stuart Ritchie’s direct but fair review of The Gene, and found out that he’d written his own book.

I wasn’t sure what to expect, but viewed it as a worthwhile pickup because intelligence is a fascinating topic and Ritchie seemed like a thoughtful guy – and Intelligence didn’t disappoint.  More a bite-sized booklet than a book, it manages to drive home a number of mental models as well as provide some useful (and balanced) scientific review of the type completely absent from Mukherjee’s murky mention of the topic (see my review of, and notes on, The Gene).

Highlights: Ritchie is balanced, presenting the science and the debate thereon in its totality.  Inadvertently, he also provides some of the best quantitative evidence for the mental models approach that I’ve seen anywhere; to the extent that intelligence is highly linked to superior outcomes for wealth, health, and happiness, and concomitantly, the most likely “mechanism” thereof is better ability to solve problems and make decisions, the research on IQ provides a very strong rationale for prioritizing building a better worldview.  Maybe we should take Munger literally when he says that rationality is worth 50 points of IQ.

Lowlights: If anything, the book is a little too brief, and could have benefited from digging a little deeper into the science in some areas rather than just providing the “movie trailer” and moving on.

Mental Model / ART Thinking Pointscorrelation  vs. causation ,   multicausalityschemabottleneck,availability heuristic, trait adaptivityprobabilistic thinkingbase ratesmemorynonlinearity,

You should buy a copy of Intelligence if: you want an accessible, balanced, thoughtful scientific discussion of one of the most important qualities of human existence.

Reading Tips: Ritchie references a lot of research; some of the papers I’ve read on intelligence (including one on GCTA) are surprisingly readable.  Consider looking up and reviewing some of the source materials yourself, as they’ll enhance your learning.  Also, if the rest of the “All That Matters” series is as well-executed as this one, they may be worth investigating…

Pairs Well With:

Other Minds” by Peter Godfrey-Smith (OthM review + notes).  Truly an unexpected joy, this phenomenal book about octopus intelligence and its similarities to and differences from human intelligence is an under-the-radar gem.

The Violinist’s Thumb” by Sam Kean (TvT review + notes).  While it doesn’t sum up the Central Dogma as elegantly as Mukherjee’s The Gene, it has a lot more applicability to everyday life and is uncluttered by The Gene’s inappropriate injection of sociopolitical commentary.

Seeking Wisdom” by Peter Bevelin (SW review + notes) and “Poor Charlie’s Almanack” by Charlie Munger (PCA review + notes).  “ Intelligence” is not a stationary variable; it can grow over time, but also (in certain senses) predictably declines as we age.  This requires increasing utilization of “crystallized intelligence” to make up for declining speed, similar to how older athletes must succeed on technique rather than raw athletic ability… and building judgment would seem to be the best way to do that.

The Design of Everyday Things” by Don Norman ( DOET review + notes), one of the best books around on how to apply intelligence to make the world function better.

Reread Value: 2/5 (Low) – unless you’re going back to go deeper into the sources.

More Detailed Notes + Analysis (SPOILERS BELOW):

IMPORTANT: the below commentary DOES NOT SUBSTITUTE for READING THE BOOK.  Full stop. This commentary is NOT a comprehensive summary of the lessons of the book, or intended to be comprehensive.  It was primarily created for my own personal reference.

Much of the below will be utterly incomprehensible if you have not read the book, or if you do not have the book on hand to reference.  Even if it was comprehensive, you would be depriving yourself of the vast majority of the learning opportunity by only reading the “Cliff Notes.”  Do so at your own peril.

I provide these notes and analysis for five use cases.  First, they may help you decide which books you should put on your shelf, based on a quick review of some of the ideas discussed.  

Second, as I discuss in the memory mental model, time-delayed re-encoding strengthens memory, and notes can also serve as a “cue” to enhance recall.  However, taking notes is a time consuming process that many busy students and professionals opt out of, so hopefully these notes can serve as a starting point to which you can append your own thoughts, marginalia, insights, etc.

Third, perhaps most importantly of all, I contextualize authors’ points with points from other books that either serve to strengthen, or weaken, the arguments made.  I also point out how specific examples tie in to specific mental models, which you are encouraged to read, thereby enriching your understanding and accelerating your learning.  Combining two and three, I recommend that you read these notes while the book’s still fresh in your mind – after a few days, perhaps.

Fourth, they will hopefully serve as a “discovery mechanism” for further related reading.

Fifth and finally, they will hopefully serve as an index for you to return to at a future point in time, to identify sections of the book worth rereading to help you better address current challenges and opportunities in your life – or to reinterpret and reimagine elements of the book in a light you didn’t see previously because you weren’t familiar with all the other models or books discussed in the third use case.

Page 2: Ritchie starts the book with the (correct) observation that, ironically, smart people don’t like the idea of intelligence.”  Whether they like it or not, it exists and it’s important.

Page 5: Ritchie references Sir Francis Galton, who many readers will have seen elsewhere – in Jordan Ellenberg’s “How Not To Be Wrong (HNW review + notes) as well as Mukherjee’s The Gene (TG review + notes).

Page 7: The first quantitative attempt at creating an intelligence test was Alfred Binet in the early 1900s; the goal was humanitarian (i.e. to help children get the appropriate attention).

Page 10 – 11: Like Mukherjee, Ritchie comes across as anti-eugenics, which is not particularly notable (since most modern people are anti-eugenics.)  What is notable, however, is that unlike Mukherjee, he doesn’t let the stain of eugenics bias his view of intelligence research; Ritchie notes insightfully that:

 “facts, after all, have no necessary moral or policy implications: it is up to us to decide what to do about them.”

Pages 14 – 15: While not as extensive a discussion as is present in, say, the aforementioned How Not To Be Wrong by mathematician Jordan Ellenberg, Ritchie here does a pretty solid job of very briefly summing up correlation vs. causation.

Pages 19 – 23: The overview of what is covered on intelligence tests, ranging from analytical reasoning / pattern recognition to memory and knowledge, is pretty interesting; while you might intuitively wonder what knowledge has to do with intelligence, there’s actually some ground to believe it can improve the latter (see Ian Leslie’s Curious, for example – at least part of it – C review + notes).  Ritchie notes that IQ scores do vary on retests, which is not surprising, considering the impact of various external factors on cognitive ability.

Pages 24 -25, Pages 28 – 29: abcd: The interesting conclusion here is that while, naturally, some people will be better at some subtests than others, there is a very strong underlying correlation, somewhat similar to overall physical fitness (even though some people will naturally be better at strength or cardio).  Ritchie does note, importantly, that “g” (IQ):

“doesn’t explain everything about mental abilities.”  

So it’s a straw man for detractors to assume that it attempts to.

Page 27: In a little sidebar, Ritchie points out the unscientific nature of Gardner’s “multiple intelligences,” a concept that nonteheless holds a lot of cachet among certain groups.

Pages 32 – 33: One of the really important findings in the research is that fluid intelligence (the ability to figure things out without prior knowledge) and speed decline rapidly over time; this is a well-known phenomenon in mathematics and to some extent, I’ve even observed it in the investing world (via self-reports from older investors).  Michael Mauboussin references it in The Success Equation (TSE review + notes) as well.

This is naturally related to the aging process. Importantly, however, “crystallized” intelligence actually increases over time, even post-education, well into late middle age, due to the compounding effect of more knowledge offsetting the naturally slower speed.

Cross-reference my earlier note about wide receivers and route running – this is a great reason to invest in building out a solid worldview.

Pages 35 – 36: Ritchie discusses the correlation between intelligence during childhood and late adulthood, and mentions that physical exercise can slow cognitive decline.

Page 41: Correlation between g and school performance is very high.

Page 45: Ritchie addresses, and dismisses, the social class argument (which is, vaguely, what Mukherjee was sort of getting at, maybe, it’s hard to tell.)  He returns to this multicausality issue later, but notes, summarily, that social class does have impacts on IQ, which doesn’t in any way invalidate that g exists.

Page 48: Higher IQ is linked to substantially lower all-cause mortality; some studies find an effect similar to smoking, to give you an idea of how big a difference that is.

Ritchie doesn’t really go deeply into it, but postulates elsewhere (reasonably) that the mechanism is better decision-making.

Page 52: Ritchie also notes that intelligence is correlated with creativity, though again, he does a good job of pointing out the other contributing factors.

Pages 56 – 57: Ritchie notes that there’s no statistical correlation between high intelligence and poor social skills; my view is that it may just be an availability heuristic or  schema bottleneck of the sort discussed in Jordan Ellenberg’s “ How Not To Be Wrong on pages 361 – 362 regarding the seeming inverse correlation between attractiveness and kindness in prospective dating partners.

Ellenberg makes the case, essentially, that even if the traits were evenly and randomly distributed, there’s some sort of threshold of attractiveness where you’re never going to notice the “mean uglies” anyway – in a friendship or professional context, perhaps you only choose to associate with people who have some combination of intelligence and social skills.

If someone is dumb and has no social skills, you’re not likely to even spend enough time around them to notice.  On the other hand, maybe there’s someone in your life who you’re friends with because you’re wowed by their intelligence… but over time you keep noticing they’re not really very nice people.  (I’ve had this happen to me a lot.) On the other hand, all the not-intelligent, not-nice people never even come across your radar, because if you meet someone who doesn’t seem nice orintelligent, they don’t make it to the point of having a relationship with you.

None of this is to suggest that there couldn’t perhaps be a weak inverse correlation between IQ and social skills… but it’s likely not as universal as stated.

Pages 60 – 61, Page 63: Ritchie brings up the concept of trait adaptivity in correlation to intelligence.  Comparing the human brain to a small army with lots of technology, Ritchie points out that we win not on size and strength, not just in terms of our bodies, but also in terms of the size of our brains.

He also brings up, extremely briefly, the energy costs of cognition. Godfrey-Smith discusses the trait adaptivity angle of cognition in way more depth in “Other Minds” OthM review + notes), which, can I just reiterate, knocks my socks off.

Meanwhile, Jennifer Ackerman discusses this topic in The Genius of Birds (Birds review + notes)… and also observes, there, the limited correlation between bird brain size and intelligence.

As does Sam Kean on pages 221 – 230 of “ The Violinist’s Thumb – TVT review + notes.

Fun fact, our brains have gotten smaller over the past 30,000 years!

Pages 65 – 66: Twin studies are mentioned here; they come up a lot in biology/genetics.  Ritchie here presents some of the data on heritability of intelligence, which I discuss in a lot more depth in my review of and notes on Siddhartha Mukherjee’s “The Gene” – TG review + notes.

Pages 69 – 70: Ritchie here notes that underpriviliged environments can “stifle, to some extent, the intellectual potential that lies in a child’s genes.”  

This is an example of a bottleneck: intelligence is a multicausal phenomenon that relies both on genetics and environment.  When the environment is the limiting reagent – i.e., there’s not enough food to support brain development, or other things – then genes can’t reach their full potential.

Page 71: Ritchie notes that, like many complex traits, intelligence is “polygenic.”  So there’s not a singular “gene” for intelligence, but rather a lot of small impacts from a lot of small genes… another example of multicausality.

Pages 75 – 78: Ritchie here discusses myelination, white matter, brain connectivity, and fMRI studies, which are touched on in various places by Cal Newport’s “ Deep Work (DpWk review + notes) and Alex Soojung-Kim Pang’s “Rest” – Rest review + notes.

Page 82: Ritchie briefly touches on probabilistic thinking and base rates here, implicitly – in any given individual’s life, there are of course so many variables that higher intelligence may or may not result in longer lifespan or any other positive effect.  But averaged across the population, the base rate of any meaningful life outcome is meaningfully improved by higher intelligence.

Page 84: No, playing Mozart will not make your baby smarter.

Page 86: Another little piece of evidence suggesting that memory training isn’t very helpful…

Page 88: Ritchie touches on the multicausality / bottleneck issue discussed above, noting that, for example, tapeworms might cause lower intelligence in children in developing countries by competing with the brain for resources.  He also notes the dose-dependency / nonlinearity issue: for example, even though iodine supplementation helps iodine-deficient kids become smarter, that doesn’t mean that those of us who eat plenty of iodized salt need to rush out and take iodine.

Pages 91 – 92, Pages 94 – 97: Ritchie notes that education is one of the few things that can reliably raise IQ; he also notes the “Flynn Effect,” which basically means we’re getting smarter over time.  There is some suggestive evidence for the idea that we’re removing bottlenecks, whether via better education or better nutrition – he notes that certain subtest scores (like those on speed) don’t increase.


First Read: spring 2018

Last Read: spring 2018

Number of Times Read: 1


Review Date: spring 2018

Notes Date: spring 2018