In this post, part of our PB101: Foundations of Psychological Science series, David Feng (BSc Psychological and Behavioural Science) explores the nature and evolution of human intelligence, drawing on research from across the discipline, putting our unique cultural knowledge into context.

You carry within you a body of knowledge and capacity for thought that’s unique to where you come from and who you are.

We are scoring increasingly higher on measurements of intelligence. In fact, since 1948, IQ has consistently increased in the global population 9 to 15 points every 30 years (Gray & Bjorklund, 2018), albeit slowing down nearing this century (Sundet, Barlaug and Torjussen, 2004). This pattern of rapidly increasing IQ scores is termed the Flynn effect, and should it persist, Folger (2012) projects that our descendants will have almost 30 points over us. This is the difference between average intelligence and the top 2 percent of today’s population.

The continuous, substantial gain in IQ across culture, geography, and time raises a key question: how are we getting so smart so quickly? With possible explanations ranging education, test-taking ability, nutrition and genetics, at the ultimate level, our intelligence is fundamentally shaped by our cumulative cultural knowledge and its constituent products.

What is intelligence, anyway?

Intelligence, measured through IQ tests, is an individual’s capacity for reasoning, problem solving and acquiring novel knowledge within fixed and changing environments (Gray & Bjorklund, 2018). It’s not only what you know about old environments, but also what you can do in new ones. Appropriately, Cattell (1971) partitioned intelligence into two factors: crystallised and fluid intelligence.

Crystallised intelligence reflects your ability to retain previous experiences and knowledge, commonly measured through information, arithmetic, and vocabulary tests. Who won the Nobel Price last year? What’s the product of 11 and 88? What does the word ‘serendipity’ mean? These are all tests of crystallised intelligence: what you already know.

Fluid intelligence captures your capacity for abstraction and problem solving. Spotting the pattern of a black square moving along a grid and understanding how the 2×2 Lego block fits with the 2×4 block without prior experience are examples of one’s ability to deal with novel problems.

Regardless of the particular test, all cognitive abilities are positively correlated with an underlying ‘general’ intelligence (g). Known as the g factor, Charles Spearman found that high scorers on any single test tend to score high on other tests (Gray & Bjorklund, 2018). Additionally, g was found in 31 non-Western nations, suggesting its prevalence as a universal human trait (Warne and Burningham, 2019).

Previous research illustrates IQ gains in the United States between 1948 and 2002, were most prominent in Raven’s progressive matrices – a standard measurement of fluid intelligence – while Information, arithmetic and vocabulary tests showed significantly less growth. This data suggests two questions: first, why are we seemingly getting smarter? And secondly, why has our fluid intelligence increased dramatically while crystallised intelligence remain relatively fixed?

Culture and Intelligence

If we explore the Flynn effect through a cultural perspective, both of these problems are easier to understand. Cultural knowledge increases the complexity of daily life, driving fluid intelligence. As information is transmitted from one generation to the next, humans have made culture cumulative. Meaning, no individual human can recreate their world within a lifetime (Muthukrishna & Henrich, 2016). In Dual Inheritance theory, each successive generation inherits both a genetic and cultural line, resulting in more advanced institutions, technologies and languages than the last (Henrich, 2015).

While some would argue that societal advancements are developed by a selective few, Michael Muthukrishna and Joseph Henrich’s ‘Innovation in the collective brain’  (2016) dispels this myth. Instead, the authors posit that innovation is largely due to ‘serendipity, recombination, and incremental improvement’, all a product of culturally transmitted information. Accidental discoveries such as the x-ray, penicillin, and Post-it notes are made possible through the appropriate cultural exposure. Similarly, the constant rearrangement of cultural knowledge allow individuals to manage scientific breakthroughs. Without a cumulative culture, incremental improvements across generations are not possible.

Rather than attributing IQ gains to purely evolutionary terms, we now see that it is society’s increasing sophistication that elevates demand on our cognitive abilities. Indeed, when Wicherts, Borsboom and Dolan (2010) aligned estimates of national IQ with developmental data consisting of variables likely to contribute to the Flynn effect, they found a ‘strong relationship between … environmental variables and estimates of average IQ’, concluding that national IQ could just be another indicator of development.

Admittedly, we face the issue of reverse causality: IQ could be a proponent, rather than a product, of development. The authors illustrate that IQ gains are greatest in developing nations while stagnating in developed ones, suggesting that gains follow, rather than lead development. However, this is just one interpretation. Most likely, both directions are in play. For instance, formal schooling’s positive effect on IQ may be contingent upon IQ gains conducive to establishing such institutions in the first place (Ritchie and Tucker-Drob, 2018).

Why culture?

Alternative explanations of the Flynn effect are proximate (mechanisms) and inevitably involve cumulative culture.

Some propose that heredity account for the Flynn effect. Indeed, IQ seems to be heritable, increasingly with age and socioeconomic status (Nisbett et al, 2012). Moreover, Mingroni (2007) claims that heterosis – mating between genetically distinct subpopulations – produces IQ gains. However, Uchiyama, Spicer and Muthukrishna (2020) notes that heritability does not imply a trait is primarily genetic and the short time-frame of IQ gains suggest that heritability is amplified by culture.

The authors’ emphasis that genetic contributions must be evaluated in light of prior cultural contributions serves a counter-point to Lynn (2009)‘s position of nutrition. By illustrating the effect of nutrition on Developmental Quotients -analogous of IQ- among infants, Lynn attempts to eliminate the involvement of culture. However, it is the uniformity of culture and environment that enables proximate mechanisms – such as better nutrition – to take effect.

Smarter, yes. Smarter, no.

Despite the impact of culture on our intelligence, we would be mistaken to conclude that we have grown smarter than our ancestors because in evolutionary terms, ‘smart’ is contextual.

While we might have stronger abstraction skills due to newly developed constituents of culture such as technology, formal education and scientific thinking, Flynn (2007) reiterates that our ancestors’ intelligence were anchored in everyday reality and concrete situations. This important clarification supplies a plausible response to our second question: while fluid intelligence has increased dramatically due to the demand for abstraction because of cultural development, crystallised intelligence sees much more modest gains as our fixed knowledge about the world changes in content but less in capacity.

Ultimately, the Flynn effect is indicative of the cumulative cultural knowledge that we have transmitted over time. This cultural knowledge bring about the institutions and practices that in turn shape our intelligence, predisposing us to think differently. You carry within you a body of knowledge and capacity for thought that’s unique to where you come from and who you are.

Notes:

• The views expressed in this post are of the author and not the Department of Psychological and Behavioural Science or London School of Economics and Political Science (LSE).
• This blog post was originally written as part of PB101: Foundations of Psychological Science, a compulsory course on the BSc Psychological and Behavioural Science programme in the Department of Psychological and Behavioural Science at LSE. It has been published with the permission of the author. Visit the PBS website for more information on studying in the department: https://www.lse.ac.uk/PBS/Study.
• Photo by Rodolfo Clix from Pexels

References

Cattell, R. B. (1971). Abilities: Their structure, growth, and action. Boston, MA: Houghton Mifflin. (Rev. ed.: Amsterdam: North-Holland, 1987.)

Flynn, J. R. (2007). What Is Intelligence? Cambridge: Cambridge University Press.

Folger, T. (2012). Can We Keep Getting Smarter? Scientific American, 307(3), 44-47. Retrieved November 11, 2020, from http://www.jstor.org/stable/26016077.

Gray, Peter O, & Bjorklund, David. (2018). Psychology. New York: Macmillan Learning.

Henrich, J. (2015). The secret of our success. Princeton: Princeton University Press.

Lynn, R. (2009). What has caused the Flynn effect? Secular increases in the Development Quotients of infants. Intelligence (Norwood), 37(1), 16-24.

Mingroni, M. A. (2007). Resolving the IQ Paradox. Psychological Review, 114(3), 806-829.

Muthukrishna, Michael, & Henrich, Joseph. (2016). Innovation in the collective brain. Philosophical Transactions. Biological Sciences, 371(1690), 20150192.

Nisbett, Richard & Aronson, Joshua & Blair, Clancy & Dickens, William & Flynn, James & Halpern, Diane & Turkheimer, Eric. (2012). Intelligence New Findings and Theoretical Developments. The American psychologist. 67. 130-59. 10.1037/a0026699.

Ritchie, Stuart J, & Tucker-Drob, Elliot M. (2018). How Much Does Education Improve Intelligence? A Meta-Analysis. Psychological Science, 29(8), 1358-1369.

Sundet, J, Barlaug, D, & Torjussen, T. (2004). The end of the Flynn effect? A study of secular trends in mean intelligence test scores of Norwegian conscripts during half a century. Intelligence (Norwood), 32(4), 349-362.

Uchiyama, Ryutaro & Spicer, Rachel & Muthukrishna, Michael. (2020). Cultural Evolution of Genetic Heritability. 10.1101/2020.06.23.167676.

Warne, Russell T, & Burningham, Cassidy. (2019). Spearman’s g Found in 31 Non-Western Nations: Strong Evidence That g Is a Universal Phenomenon. Psychological Bulletin, 145(3), 237-272.

Wicherts, Jelte M, Borsboom, Denny, & Dolan, Conor V. (2010). Why national IQs do not support evolutionary theories of intelligence. Personality and Individual Differences, 48(2), 91-96.