Variation in general intelligence and our evolutionary history

In a bit of “TMI”, I’m far more intellectually promiscuous than I am in my personal life. My primary focus on this blog, if I have one, is probably historical population genetics of the sort highlighted in David Reich’s Who We Are and How We Got Here. But I have plenty of other interests, from economic history to cognitive psychology. Like religion, I have precise and clear opinions about a topic like “intelligence.” Unlike many people with an interest in evolutionary genetics I have read psychometric work, am familiar with some of the empirical results, as well as being personally acquainted with people in the field of psychometrics.

A few days ago Nassim Nicholas Taleb opined on intelligence, and I was silent. Today some individuals who I know from within the field of cultural evolution, another one of my interests, discussed intelligence, and I was silent. I’ve said all I really have to say over 15 years, and it isn’t as if I reanalyze psychometric data sets. But, a question that Taleb acolytes (and presumably Taleb) have brought up is if intelligence is such an important heritable trait, why isn’t everyone much smarter?

Think of this as the second Von Neumann paradox. What I’m alluding to is the fact that we know for a fact that human biology is capable of producing a god-made-flesh. With all due respect to another Jew who lived 2,000 years earlier than him, I speak here of John Von Neumann. We know that he is possible because he was. So why are the likes of Von Neumann bright comets amongst the dust of the stars of the common man, rather than the norm?

First, consider the case of Von Neumann himself. He had one daughter and two grandchildren. That is, within two generations genetically there was less “Von Neumann” than there had been. Though his abilities were clearly mentat-like, from the perspective of evolution Von Neumann was not a many sigma individual. He was within the normal range. Close to the median, a bit below in fecundity and fitness.

Taking a step back and focusing on aggregate populations, the fact that intelligence seems to be a quantitative trait that is at least moderately heritable and normally distributed due to polygenic variation tells us some things evolutionarily already. In Principles of Population Genetics is noted that heritable quantitative traits are often those where directional selection is not occurring due to huge consistent fitness differentials within the population.

Breaking it down, if being very smart was much, much, better than being of average smarts, then everyone would become very smart up to the physiological limit and heritable genetic variation would be removed from the population. Characteristics with huge implications for fitness tend not to be heritable because natural selection quickly expunges the deleterious alleles. The reason that fingerprints are highly heritable is that the variation genetically is not much impacted by natural selection.

The fact that being very intelligent is not evolutionarily clearly “good” seems ridiculousness to many people who think about these things. That’s because if you think about these things, you are probably very good at thinking, and no one wants to think that what they are good at is not evolutionarily very important. The thinking man cannot comprehend that thinking is not the apotheosis of what it is to be a man (similarly, the thinking religious man sometimes confuses theological rumination with the heights of spirituality; reality is that man does not know god through analysis, man experiences god).

So let’s talk about another quantitative trait which is even more heritable than intelligence, and easier to measure: height. In most societies males, in particular, seem to be more attractive to females if they are taller. As a male who is a bit shorter than the American average, it is obvious that there is some penalty to this in social and potentially reproductive contexts. And yet there is normal variation in height, and some populations seem to be genetically smaller than others, such as the Pygmy peoples of the Congo rainforest. Why?

Though being a tall male seems in most circumstances to be better in terms of physical attractiveness than being a short male, circumstances vary, and being too tall increases one’s mortality and morbidity. Being larger is calorically expensive. Large people need to eat more because they have larger muscles. Selection for smaller size in many marginalized rainforest populations is indicative of the fact that in such calorically challenging environments (humans in rainforests have to work hard to obtain enough calories in a hunter-gatherer context), the fitness gain due to intrasexual competition is balanced by reduced fitness during times of ecological stress as well as individual correlated responses (very large males die more often than smaller males).

Additionally, for height I mentioned the sexual component: there does not seem to be a necessary association with higher reproductive fitness with being a tall woman. Though this is subject to taste and fashion, there is likely some antagonistic selection across the two sexes at work, where tall men are the fathers of taller daughters, whose reproductive fitness may actually be lower than smaller women. And vice versa, as short men may produce more fit short daughters (though again, this depends on ecological context and cultural preconditions).

Being very large impacts fitness through the genetic correlation of size with other characteristics. Very large males are subject to higher risk for sudden tears in their lungs, or suboptimal cardiac function. Humans select chickens to be very large in the breast for food, but these chickens can barely walk, and may not be able to reproduce without assistance. Evolution in a quantitative genetic sense may then be all about trade-offs.

So let’s go back to intelligence. What could be the trade-offs? First, there are now results presented at conferences that very high general intelligence may exhibit a correlation with some mental pathologies. Though unpublished, this aligns with some prior intuitions. Additionally, there is the issue where on some characteristics being “species-typical” increases reproductive fitness (an average size nose), while in other characteristics being at an extreme is more attractive (very curvy women with large eyes and small chins; secondary sexual characteristics). Within intelligence, one could argue that being too deviated from the norm might make socialization and pair-bonding difficult. Here is an anecdote about the genius Von Neumann:

Neumann married twice. He married Mariette Kövesi in 1930. When he proposed to her, he was incapable of expressing anything beyond “You and I might be able to have some fun together, seeing as how we both like to drink.”

Apparently having a very fast analytic mind which can engage in abstraction and conceptual manipulation does not mean that one can come up with anything better than that when it came to procuring a mate. And procuring a mate is one of the only “good” things from an evolutionary perspective.

The human mind is neither universally plastic, nor it is a prefabricated set of specialized modules. It is a mix of both. We clearly have some “pre-loaded” code, such as the ability to recognize faces intuitively and rapidly (which a small proportion of the population lacks). But other competencies develop over time, co-opting neurological architecture that grew organically for other purposes. In Reading in the Brain Stanislas Dehaene recounts how the region which specializes in the ability to recognize letter shapes is a preexistent visual-spatial module, probably developed for ecological adaptation to environments where recognition of various organic and inorganic objects was of fitness relevance (obviously now tied in to regions of the brain geared toward verbal comprehension). Dehaene even seems to suggest there may be a trade-off between various cognitive capacities when comparing individuals from urban developed societies and individuals from non-literate small-scale societies.

As human societies have specialized over the last 10,000 years a small number of people who naturally were on the end of a particular distribution in abstraction-and-analysis ability began to preferentially fill exotic niches that had previously not existed. From all we can tell the ancient polymath Archimedes was a Von Neumann for his age. Archimedes seems likely to have been of aristocratic background, and part of the class of leisured intellectuals. The fact that he had such innate talent and disposition, combined with his life circumstances, was simple happenstance.

Today we live in a different age. Specialization, and the post-industrial economy, put a premium on competencies associated only with individuals on the “right tail” of the IQ distribution. Similarly, our genetic background predisposes many of us to obesity because the modern environment is “obesogenic.” The reality is that obesity was not an issue for almost all of human history, so genetic variation (often behavioral/cognitive) that is associated with obesity today was not so associated with it in the past. There could be no selection against obesity when it wasn’t a trait within the population.

Just as the modern environment is potentially “obesogenic,” it is also potentially “intelligenic.” Here’s what I’m talking about, The Science Behind Making Your Child Smarter:

The research also lends insight into why many apps and training programs aimed at raising IQ fail to produce lasting effects, says Elliot Tucker-Drob, an associate professor of psychology at the University of Texas at Austin, and co-author of the study.

Raising IQ may require the kind of sustained involvement that comes with attending school, with all the practice and challenges it entails. “It’s not like you just go in for an hour of treatment a week. It’s a real lifestyle change,” he says


To be a “nerd” is a lifestyle only possible in the modern information-rich environment. The Flynn effect is evidence that changing environments can shift the whole distribution. But just as with obesity or adult-onset diabetes risk, there is also heritable variation latent across the genome that seems to affect one’s response to the intelligenic environment.

Humans have large brains for our size. We are smarter than other primates. But evolutionary genetics today seems to be coming to the conclusion that it wasn’t a quantum jump, but gradual selection and change. Having a very low intellectual capacity was probably correlated with low fitness in the past (though small brains are calorically less greedy).

But, having a very high general intelligence does not seem to have resulted in that great of a gain in social or cultural status in comparison to being of normal intelligence. In fact, if the genetic correlation is such that it’s associated with some higher risk for mental instability, it could simply be that a form of stabilizating selection over time kept humans within the “normal range” because that was evolutionarily optimal. Be smart enough. But not too smart that you are weird.

And, as theorists from cultural evolution have observed, we are a “hive-mind” which leverages collective wisdom. Most of us don’t have to derive mathematical equations, we can use the formula provided to us. Though it’s useful to have a few people around who can invent statistics that the rest of us use…

On the anniversary of the publication of the On The Origin of Species

Today on this date Charles Darwin’s On The Origin of Species was published. If you haven’t, you should read it. I’m not sure if it’s the most influential book of the last few centuries, but it’s definitely up there.

That being said, sometimes people want to read something different that’s more recent. I would highly recommend Evolution: The First Four Billion Years. It’s an anthology of different thinkers from evolutionary biology, from paleontology, to genetics, and even to philosophy.

But evolution converges!

Stephen Jay Gould became famous in part for his book Wonderful Life: The Burgess Shale and the Nature of History. By examining the strange creatures in the Burgess Shale formation Gould makes the case that evolution is a highly contingent process, and that if you reran the experiment of life what we’d see might be very different from what we have now.

But the scientist whose study of the formation that inspired Gould’s interpretation, Simon Conway Morris, had very different views. Though it can sometimes be churlish, his rebuttal can be found in The Crucible of Creation: The Burgess Shale and the Rise of Animals. Simony Conway Morris does not believe that contingency is nearly as powerful a force as Gould would have you believe. And his viewpoints are influential. Richard Dawkins leaned on him to make the case for convergence in evolution in The Ancestor’s Tale.

This crossed my mind when reading Carl Zimmer’s new column, When Dinosaurs Ruled the Earth, Mammals Took to the Skies:

Today, placental mammals like flying squirrels and marsupials like sugar gliders travel through the air from tree to tree. But Volaticotherium belonged to a different lineage and independently evolved the ability to glide.

They were not the only mammals to do so, it turns out. Dr. Luo and his colleagues have now discovered at least two other species of gliding mammals from China, which they described in the journal Nature.

Dr. Meng said that the growing number of fossil gliders showed that many different kinds of mammals followed the same evolutionary path. “They did their own experiments,” he said.

This ultimately comes down to physics. There are only so many ways you can make an organize that flies or glides. Mammals come to the table with a general body plan, and that can be modified only so many different ways.

This is not a foolproof point of datum in favor of convergence as opposed to contingency. Frankly these are often vague verbal arguments which are hard to refute or confirm. And even molecular evolutionary analyses come to different conclusions. It may be that we are asking the wrong question. But, it does suggest that evolution may work in a much narrower range of parameters as time progresses because of the winnowing power of selection.

What determines the rate of evolution

The tweet above from Wiley relates to a paper, Polygamy slows down population divergence in shorebirds. It’s a cool paper. I tweeted it. But does it relate to the “rate of evolution”?

There’s no definitive answer to this question. Different people will have different answers, as it was evident on Twitter. For me my surprise was due to my definition for what evolution is: change is allele frequencies over time. This is far more fundamental than speciation. But then I don’t think much about speciation.

Some people brought up divergence. But divergence for me is not necessary, a population could remain unitary but exhibit large allele frequency changes. Then again, if you study phylogenetics on a macroevolutionary scale, as most people who study phylogenetics do, then you would focus on divergence.

The logic of human destiny was inevitable 1 million years ago

Robert Wright’s best book, Nonzero: The Logic of Human Destiny, was published nearly 20 years ago. At the time I was moderately skeptical of his thesis. It was too teleological for my tastes. And, it does pander to a bias in human psychology whereby we look to find meaning in the universe.

But this is 2017, and I have somewhat different views.

In the year 2000 I broadly accepted the thesis outlined a few years later in The Dawn of Human Culture. That our species, our humanity, evolved and emerged in rapid sequence, likely due to biological changes of a radical kind, ~50,000 years ago. This is the thesis of the “great leap forward” of behavioral modernity.

Today I have come closer to models proposed by Michael Tomasello in The Cultural Origins of Human Cognition and Terrence Deacon in The Symbolic Species: The Co-evolution of Language and the Brain. Rather than a punctuated event, an instance in geological time, humanity as we understand it was a gradual process, driven by general dynamics and evolutionary feedback loops.

The conceit at the heart of Robert J. Sawyer’s often overly preachy Neanderthal Parallax series, that if our own lineage went extinct but theirs did not they would have created a technological civilization, is I think in the main correct. It may not be entirely coincidental that the hyper-drive cultural flexibility of African modern humans evolved in African modern humans first. There may have been sufficient biological differences to enable this to be likely. But I believe that if African modern humans were removed from the picture Neanderthals would have “caught up” and been positioned to begin the trajectory we find ourselves in during the current Holocene inter-glacial.

Luke Jostins’ figure showing across board encephalization

The data indicate that all human lineages were subject to increased encephalization. That process trailed off ~200,000 years ago, but it illustrates the general evolutionary pressures, ratchets, or evolutionary “logic”, that applied to all of them. Overall there were some general trends in the hominin lineage that began to characterized us about a million years ago. We pushed into new territory. Our rate of cultural change seems to gradually increased across our whole range.

One of the major holy grails I see now and then in human evolutionary genetics is to find “the gene that made us human.” The scramble is definitely on now that more and more whole genome sequences from ancient hominins are coming online. But I don’t think there will be such gene ever found. There isn’t “a gene,” but a broad set of genes which were gradually selected upon in the process of making us human.

In the lingo, it wasn’t just a hard sweep from a de novo mutation. It was as much, or even more, soft sweeps from standing variation.

When the gods come crashing down

Sometimes the old gods slowly fade into oblivion. Contrary to popular perception this seems likely the case for ancient paganism. The conversion of Constantine to the Christian religion began the process of a hand-off and the commanding heights of classical culture that took over a century to complete. There were punctuating moments, such as the apostasy of Julian in the 360s, or the mostly symbolic ban on public paganism by Theodosius in the 390s (the Serapeum was destroyed by a vigilante mob). But pagans in the form of the Neoplatonic school persisted into the 6th century, while elite pagans such as Marcellinus maintained power and influence deep into the second half of the 5th century.

Call this “normal” cultural evolution. Antiquity evolved from being predominantly pagan to predominantly Christian (though a small cultured pagan minority persisted even until the Islamic conquest in the Near East, such as the Sabians of Haran).

The Reformation period was different. In a single generation one thousand years of a coherent and unified Western Christian ideology collapsed, and was replaced by something very different.

Note here that I said Western Christian ideology. The reality is that Western Christianity was never as unified or coherent as Western Christians themselves envisaged themselves to be (or aspired to be). There were episodes of hostility between particular kingdoms and the Roman papacy. Heresies such as that of the Cathars, and popular revolts with a religious tinge such as that of the Hussites. And finally, there were periods of multiple popes, which undermined the credibility of the institution of the Church in the medieval period.

But all this pales next to the magnitude and scope of the revolt against the establishment of the Western Christian church that occurred in the 1520s. Martin Luther went from being a Christian cleric within the established Church to declaring the pope the anti-Christian! Previously devout peasants in Switzerland turned on the relics and churches which they had only recently venerated, and engaged in mob iconoclasm. Whereas monarchs, such as Henry IV, ultimately compromised with the clerical estate (or, submitted), Henry VIII of England managed to destroy or subordinate the institutions of the church to his own will and pleasure.

There are many theories for why the Reformation occurred when it did. Some of them are rooted in technology, in particular the printing press. Others point to the development of proto-national identities, such as the rise of German nationalism and its leveraging by Luther against his “Roman” persecutors.

These specific issues are not interesting to me. Rather, what they point out to us that there can be cultural revolutions that occur very rapidly. One can point to the pacific post-World War II Japanese, and contrast them with the militaristic Japanese of the first half of the 20th century. Or the shift of Russia from being a conservative autocracy in the 1910s to a revolutionary society in the 1920s. But these are modern events, and moderns are liable to suggest that our own epoch is sui generis in these sorts of turnovers of values. But the Reformation shows that revolutionary changes in whole societies can occur rather rapidly even in a pre-modern context.

In other words, cultural revolution is not a derived characteristic of our species, but perhaps a very old one. The rapid expansion of the Austronesians. Or the radiation of non-African humanity. These come out of a vacuum, a cultural-demographic analog to the inflationary universe. But given enough time perhaps our species is simply subject to these sorts of explosions of creative change and innovation.