History of Intelligence Theories

Francis Galton Reading Recommendations

Here are some sources that begin to explain the positive side of my ambivalence about Galton:

Selected publication Comments
Hereditary genius (Galton, 1869) Galton attempts to show that talent is hereditary. The methods are crude but entertaining. Hundreds of mini-biographies, strange details, and curious asides (One of many: William Pitt’s talented niece, Lady Hester Stanhope ended her days in Syria, dressing as a man and claiming supernatural powers.). Sarah Austen is given credit for Jane’s novels.
Inquiries into human faculty and its development (Galton, 1883) This book is a romp through every weird place the human mind can go. If you like that sort of thing, you will like this very much.
“Regression towards mediocrity in hereditary stature” (Galton, 1886) It is amusing how much detail about statistics needed to be explained explicitly in 1886. The glorious scatterplot alone makes this article worth a look.
Memories of my life (Galton, 1908) Galton’s mind was sharp right up to the end of his life. Filled with anecdotes, gossip, and rich humor. Fun story about the aftermath of the Sarah/Jane Austen fiasco. Googling the quotations that Galton inserts without sourcing makes for hours of entertainment. There is also much pathos here as well.
History of Intelligence Theories

Galton’s “ridiculous” intelligence tests

As some scholars tell the story, this so-called genius Francis Galton had some pretty stupid ideas about how to measure intelligence. Instead of measuring useful things like reasoning, knowledge, and creativity, Galton measured totally irrelevant things like visual acuity, grip strength, and reaction time! What an idiot! Anyone with the least bit of common sense would realize that the senses are not the same as intelligence. Galton, as the story goes, was blinded by his philosophical allegiance to empiricism and associationism, which emphasized the primacy of the senses in explaining human knowledge and reasoning. The world would have to wait for Alfred Binet to set things right.

As it turns out, the reason that Galton measured basic sensorimotor abilities like visual acuity, grip strength, and reaction time was that he was interested in… basic sensorimotor abilities like visual acuity, grip strength, and reaction time! He was interested in them for roughly the same reasons that medical doctors, developmental psychologists, and neuropsychologists are interested in them. For example, Galton published tables showing the ages at which sensory acuity and grip strength are at their peaks and the ages at which they tend to decline. This is useful, basic research.

In reading Galton’s publications of such findings, one will find no grand pronouncements about the nature of intelligence. Galton never claimed that basic sensorimotor abilities constituted the whole of intelligence. Nevertheless it is true that, from time to time, he claimed to have found evidence that the most intellectually able tend to have greater sensitivity and sensory discrimination (Galton, 1883, p. 20), though this evidence was never formally presented. Galton had no intention of measuring intelligence directly for diagnostic purposes. He was much more interested in discovering the precursors of intelligence. Galton, instead of measuring intelligence directly, preferred to infer intelligence from measures of eminence.

Many summaries of Galton’s work report that Galton’s hypotheses about sensory acuity and intelligence failed. Within the last few decades, Galton’s hypothesis has been revived. The correlation between sensory acuity and higher cognitive abilities is indeed positive as Galton predicted, but the effect is much smaller than he expected it to be (Jensen, 2006). It is unlikely that the relationship between sensory acuity and reasoning is direct (i.e., better input→better output). It is likely that the overall health of the body manifests itself (inconsistently and probabilistically) in both the sense organs and in the brain.

What can we learn from Galton’s “ridiculous” tests? We need to understand that there is an important difference between applied research that uses intelligence tests to forecast important life outcomes and more basic research that aims to explain the foundations of intellectual ability. Galton’s research, however crude, was of the latter type. Failing to understand this distinction leads us to scoff at perfectly reasonable research. For example, it is common to come across criticisms of research that aims to understand the relation between brain size and intelligence. The correlation between brain size and intelligence appears to be on the order of ρ = 0.3 to 0.4 (Lange, Froimowitz, Bigler, Lainhart, & Brain Development Cooperative Group, 2010). Reports of such findings bring to mind frightening visions of arbitrary bureaucrats in a future dystopia granting and denying privileges to people based on the size of their heads. No sane scholar is hoping this will happen. No scholar believes that head size per se causes higher or lower intelligence. Rather, head size is an imperfect indicator of one or more developmental processes that do have a more direct influence on intelligence. Studying head size is merely a stepping stone (it is hoped) to the discovery of such processes.

Roughly the same interpretive error occurs when it is announced that IQ tests are soon to be replaced with working memory tests because researchers have found that individual differences in working memory capacity explain much of IQ tests’ predictive validity.

Such announcements miss the point. If we care about individual differences in knowledge, reasoning, and creativity, we should measure these abilities directly. The fact that working memory plays a vital role in such abilities is useful to know, but such tests only supplement our understanding of intellectual processes in individuals. They help explain what might have gone wrong (or especially right) in an individual’s cognitive development. The correlations of working memory capacity and higher-order cognitive abilities are not nearly high enough that traditional cognitive ability tests are redundant. Research on working memory capacity (or processing speed or elementary cognitive tasks) is unlikely to ever lead to a replacement of direct measures of knowledge, reasoning, and creativity. Rather, such research helps us understand the origins of individual differences in these higher-order capacities.

History of Intelligence Theories

Our debt to Francis Galton is great…and embarrassing

Francis Galton (1822–1911) was born to privilege in a highly accomplished family in Great Britain. He was also something of a child prodigy, learning to read at age two and by early childhood aptly quoting from classic poetry and literature, often to humorous effect (Terman, 1917). Galton was not a psychologist nor was he an academic researcher. He was simply a gentleman-scholar who spent his leisure time in pursuit of any scientific question that seemed interesting to him.

There are many anecdotes in circulation about Galton’s zesty and quirky approach to life, numbers, and the female form (e.g., Murdoch, 2007, pp. 10­­–11). In his autobiography, Galton (1908) comes off as a rather likeable, self-effacing, and witty person and it is easy to see how he was much admired in his day. It is not for nothing that a first-rank genius like Karl Pearson found time in his busy schedule to write a three-volume biography about him. Galton was a rebel, a rogue, a visionary, and a dynamic force—a rock star geek.

Despite all this, few of us today can express unreserved admiration for him. Although his brilliance is undeniable and his place in history secure, parts of his intellectual legacy are hard to stomach. To be fair, given the times, there was nothing unusual about his negative opinions about women, Africans, or many other groups (including Americans, whom he considered to be middling in their intellectual talents compared to the English). In fact, Galton did not have a high opinion of anyone except the most talented among us (Galton, 1869):

Every tutor knows how difficult it is to drive abstract conceptions, even of the simplest kind, into the brains of most people—how feeble and hesitating is their mental grasp—how easily their brains are mazed—how incapable they are of precision and soundness of knowledge. It often occurs to persons familiar with some scientific subject to hear men and women of mediocre gifts relate to one another what they have picked up about it from some lecture—say at the Royal Institution, where they have sat for an hour listening with delighted attention to an admirably lucid account, illustrated by experiments of the most perfect and beautiful character, in all of which they expressed themselves intensely gratified and highly instructed. It is positively painful to hear what they say. Their recollections seem to be a mere chaos of mist and misapprehension, to which some sort of shape and organization has been given by the action of their own pure fancy, altogether alien to what the lecturer intended to convey. The average mental grasp even of what is called a well-educated audience, will be found to be ludicrously small when rigorously tested. (p. 21)

On the other hand, Galton was noteworthy for going out of his way to express the bigotry of the times in scientific (and pseudoscientific) terms, providing seemingly persuasive intellectual cover for those who wished to justify ghastly acts of imperialism and genocide (e.g., proposing that the British government facilitate the colonization of Africa by Chinese immigrants, displacing the native population, Galton, 1879).

Nevertheless, Galton is rightly given credit for making important scientific advances in many fields. Among his many accomplishments, psychologists remember him primarily for his advances in statistics, behavioral genetics, and cognitive ability research.


Karl Pearson on why the idea of the correlation coefficient, not the formula, was the real breakthrough

The idea of correlation (i.e., mutual influence/intimate connection), indeed even the word correlation, existed for centuries before Francis Galton. Galton’s (1888) revolutionary idea was not that correlation exists but that it can be quantified. The correlation coefficient most often used today bears the name of statistician Karl Pearson, Galton’s friend and biographer. Though Pearson refined Galton’s formulas, providing them with a lasting and secure mathematical foundation, Pearson (1930) was quite clear that it was the idea of the correlation coefficient, not the formula, that was the real breakthrough:

Up to 1889 men of science had thought only in terms of causation, in future they were to admit another working category, that of correlation, and thus open to quantitative analysis wide fields of medical, psychological and sociological research. Turning to the writings of Turgot and Condorcet, who felt convinced that mathematics were applicable to social phenomena, we realize to-day how little progress in that direction was possible because they lacked the key—correlation—to the treasure chamber. Condorcet often and Laplace occasionally failed because this idea of correlation was not in their minds. Much of Quetelet’s work and that of the earlier (and many of the modern) anthropologists is sterile for like reasons.

Galton turning over two different problems in his mind reached the conception of correlation: A is not the sole cause of B, but it contributes to the production of B; there may be other, many or few, causes, some of which we do not know and may never know. Are we then to exclude from mathematical analysis all such cases of incomplete causation? Galton’s answer was: “No, we must endeavor to find a quantitative measure of this degree of partial causation.” This measure of partial causation was the germ of the broad category—that of correlation, which was to replace not only in the minds of many of us the old category of causation, but deeply to influence our outlook on the universe. (pp. 1–2)


Galton, F. (1888). Co-relations and their measurement, chiefly from anthropometric data. Proceedings of the Royal Society of London, 45, 135–145.

Pearson, K. (1930). The life letters and labours of Francis Galton: Volume III. Researches of middle life. Cambridge, England: Cambridge University Press.