Non-Shared Environment

Monday, May 2nd, 2016

Non-shared environment doesn’t just mean schools and peers, Scott Alexander reminds us:

The “nature vs. nurture” question is frequently investigated by twin studies, which separate interpersonal variation into three baskets: heritable, shared environmental, and non-shared environmental. Heritable mostly means genes. Shared environmental means anything that two twins have in common – usually parents, siblings, household, and neighborhood. Non-shared environmental is everything else.

At least in relatively homogeneous samples (eg not split among the very rich and the very poor) studies of many different traits tend to find that ~50% of the variation is heritable and ~50% is due to non-shared environment, with the contribution of shared environment usually lower and often negligible. This is typically summarized as “50% nature, 50% nurture”. That summary is wrong.

I mean, it’s tempting. All these social developmentalists were so sure that the way your parents praised you or didn’t praise you, or spanked you or didn’t spank you, had long-lasting repercussions that totally shaped your adult personality. The underwhelming performance of shared environment in twin studies torpedoed that whole area of study. But at least (these scholars of social behavior could tell themselves) it provided a consolation prize. The non-shared environment contributes 50% of variation, just as much as genes. That means things like your friends, your schoolteachers, and even that time you and your twin got sent away to separate camps must be really important. More than enough there to continue worrying about how society is Ruining The Children, right?

Not necessarily. Non-shared environment isn’t really “non-shared environment” the way you would think. It’s more of a dumpster. Anything that isn’t genetic or family-related gets tossed into the non-shared environment term.

Claude Shannon

Saturday, April 30th, 2016

Today would have been Claude Shannon‘s 100th birthday. What did Claude Shannon do? Quite a bit:

Claude Elwood Shannon (April 30, 1916 – February 24, 2001) was an American mathematician, electrical engineer, and cryptographer known as “the father of information theory”.[1][2]

Shannon is noted for having founded information theory with a landmark paper that he published in 1948. He is perhaps equally well known for founding digital circuit design theory in 1937, when, as a 21-year-old master’s degree student at the Massachusetts Institute of Technology (MIT), he wrote his thesis demonstrating that electrical applications of Boolean algebra could construct any logical, numerical relationship.[3] Shannon contributed to the field of cryptanalysis for national defense during World War II, including his basic work on codebreaking and secure telecommunications.

Why Iron Is the Most Underrated Factor in Health

Tuesday, April 26th, 2016

Mangan explains why iron is the most underrated factor in health, summarizing his book, Dumping Iron:

In the course of our long evolutionary history, iron has not always been abundant in our food; for this reason, as well as its critical necessity, our bodies have evolved mechanisms to grab iron and hold on to it. But we have not evolved any way of getting rid of it.

When humans are growing, they require plenty of iron for their development, but after maturity, the iron accumulates, often to high enough levels to damage cells and lead to disease.

Iron is a reactive element. When exposed to air and water, it rusts, and when inside our bodies, it can react with components of our cells — lipids, proteins, cell walls — and damage them. That’s how it leads to illness and premature aging.

A Thought Collective

Friday, April 22nd, 2016

Scientific inquiry is prone to the eternal rules of human social life:

In a 2015 paper titled Does Science Advance One Funeral at a Time?, a team of scholars at the National Bureau of Economic Research sought an empirical basis for a remark made by the physicist Max Planck: “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”

The researchers identified more than 12,000 “elite” scientists from different fields. The criteria for elite status included funding, number of publications, and whether they were members of the National Academies of Science or the Institute of Medicine. Searching obituaries, the team found 452 who had died before retirement. They then looked to see what happened to the fields from which these celebrated scientists had unexpectedly departed, by analysing publishing patterns.

What they found confirmed the truth of Planck’s maxim. Junior researchers who had worked closely with the elite scientists, authoring papers with them, published less. At the same time, there was a marked increase in papers by newcomers to the field, who were less likely to cite the work of the deceased eminence. The articles by these newcomers were substantive and influential, attracting a high number of citations. They moved the whole field along.

A scientist is part of what the Polish philosopher of science Ludwik Fleck called a “thought collective”: a group of people exchanging ideas in a mutually comprehensible idiom. The group, suggested Fleck, inevitably develops a mind of its own, as the individuals in it converge on a way of communicating, thinking and feeling.

This makes scientific inquiry prone to the eternal rules of human social life: deference to the charismatic, herding towards majority opinion, punishment for deviance, and intense discomfort with admitting to error. Of course, such tendencies are precisely what the scientific method was invented to correct for, and over the long run, it does a good job of it. In the long run, however, we’re all dead, quite possibly sooner than we would be if we hadn’t been following a diet based on poor advice.

The Sugar Conspiracy

Thursday, April 21st, 2016

The sugar conspiracy seems so brazen in retrospect:

Robert Lustig is a paediatric endocrinologist at the University of California who specialises in the treatment of childhood obesity. A 90-minute talk he gave in 2009, titled Sugar: The Bitter Truth, has now been viewed more than six million times on YouTube. In it, Lustig argues forcefully that fructose, a form of sugar ubiquitous in modern diets, is a “poison” culpable for America’s obesity epidemic.

A year or so before the video was posted, Lustig gave a similar talk to a conference of biochemists in Adelaide, Australia. Afterwards, a scientist in the audience approached him. Surely, the man said, you’ve read Yudkin. Lustig shook his head. John Yudkin, said the scientist, was a British professor of nutrition who had sounded the alarm on sugar back in 1972, in a book called Pure, White, and Deadly.

“If only a small fraction of what we know about the effects of sugar were to be revealed in relation to any other material used as a food additive,” wrote Yudkin, “that material would promptly be banned.” The book did well, but Yudkin paid a high price for it. Prominent nutritionists combined with the food industry to destroy his reputation, and his career never recovered. He died, in 1995, a disappointed, largely forgotten man.


When Yudkin was conducting his research into the effects of sugar, in the 1960s, a new nutritional orthodoxy was in the process of asserting itself. Its central tenet was that a healthy diet is a low-fat diet. Yudkin led a diminishing band of dissenters who believed that sugar, not fat, was the more likely cause of maladies such as obesity, heart disease and diabetes. But by the time he wrote his book, the commanding heights of the field had been seized by proponents of the fat hypothesis. Yudkin found himself fighting a rearguard action, and he was defeated.

Not just defeated, in fact, but buried. When Lustig returned to California, he searched for Pure, White and Deadly in bookstores and online, to no avail. Eventually, he tracked down a copy after submitting a request to his university library. On reading Yudkin’s introduction, he felt a shock of recognition.

“Holy crap,” Lustig thought. “This guy got there 35 years before me.”


Look at a graph of postwar obesity rates and it becomes clear that something changed after 1980. In the US, the line rises very gradually until, in the early 1980s, it takes off like an aeroplane. Just 12% of Americans were obese in 1950, 15% in 1980, 35% by 2000. In the UK, the line is flat for decades until the mid-1980s, at which point it also turns towards the sky. Only 6% of Britons were obese in 1980. In the next 20 years that figure more than trebled. Today, two thirds of Britons are either obese or overweight, making this the fattest country in the EU. Type 2 diabetes, closely related to obesity, has risen in tandem in both countries.

At best, we can conclude that the official guidelines did not achieve their objective; at worst, they led to a decades-long health catastrophe.


We tend to think of heretics as contrarians, individuals with a compulsion to flout conventional wisdom. But sometimes a heretic is simply a mainstream thinker who stays facing the same way while everyone around him turns 180 degrees. When, in 1957, John Yudkin first floated his hypothesis that sugar was a hazard to public health, it was taken seriously, as was its proponent. By the time Yudkin retired, 14 years later, both theory and author had been marginalised and derided. Only now is Yudkin’s work being returned, posthumously, to the scientific mainstream.

Read the whole thing.

An American Anthropologist with a Fantastic Name

Thursday, April 7th, 2016

When the Human Terrain System came up recently, Grasspunk dug up an old Adam Curtis piece on the subject:

The project was created by an American anthropologist with a fantastic name.

Montgomery McFate.

She was born in 1966. Her parents were counterculture radicals in the heart of the experimental art scene in San Francisco so she is very much “second-generation cool”. She became a punk in the Bay Area in the early 80s.

Back then she was called Mitzy Carlough.

Read the whole thing, which is actually part 9 of an article that I cited three other times: Boetti & Boetti (part 1), Astrakhan Coats and Techno-Utopianism (part 3), and Progressive Afghanistan (part 4).

Henry Harpending has died

Sunday, April 3rd, 2016

Henry HarpendingHenry Harpending has died, Gregory Cochran reports:

He suffered a stroke 3 weeks ago. Within a few days, he also had a MRSA infection in his lungs. The docs eventually cleared that, but his lungs never recovered. He died this afternoon of Adult Respiratory Distress Syndrome.

Harpending was a Professor of Anthropology at the University of Utah.

Cochran and Harpending wrote The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. I didn’t realize Steve Sailer had brought them together:

The great anthropologist Henry Harpending (1944-2016) has died. A genial polymath, Henry bridged the gap in anthropology between the old-fashioned cultural side (having spent almost 4 years in the field in Africa with Bushmen and Herero hunter-gatherers, at one point almost giving up academia to become a safari hunting guide) and the ascendant genetic side of anthropology.

It’s my honor to have brought Henry and Gregory Cochran into contact around 1999.

Slaughter at the Bridge

Sunday, April 3rd, 2016

The distant past is looking even less like the era of Conan the Corded Ware Maker as archeologists uncover a colossal Bronze Age battle:

In 1996, an amateur archaeologist found a single upper arm bone sticking out of the steep riverbank — the first clue that the Tollense Valley, about 120 kilometers north of Berlin, concealed a gruesome secret. A flint arrowhead was firmly embedded in one end of the bone, prompting archaeologists to dig a small test excavation that yielded more bones, a bashed-in skull, and a 73-centimeter club resembling a baseball bat. The artifacts all were radiocarbon-dated to about 1250 B.C.E., suggesting they stemmed from a single episode during Europe’s Bronze Age.

Now, after a series of excavations between 2009 and 2015, researchers have begun to understand the battle and its startling implications for Bronze Age society. Along a 3-kilometer stretch of the Tollense River, archaeologists from the Mecklenburg-Vorpommern Department of Historic Preservation (MVDHP) and the University of Greifswald (UG) have unearthed wooden clubs, bronze spearheads, and flint and bronze arrowheads. They have also found bones in extraordinary numbers: the remains of at least five horses and more than 100 men. Bones from hundreds more may remain unexcavated, and thousands of others may have fought but survived.

“If our hypothesis is correct that all of the finds belong to the same event, we’re dealing with a conflict of a scale hitherto completely unknown north of the Alps,” says dig co-director Thomas Terberger, an archaeologist at the Lower Saxony State Service for Cultural Heritage in Hannover. “There’s nothing to compare it to.” It may even be the earliest direct evidence — with weapons and warriors together — of a battle this size anywhere in the ancient world.

Tollense 1

The 10,000 bones in this room — what’s left of Tollense’s losers — changed all that. They were found in dense caches: In one spot, 1478 bones, among them 20 skulls, were packed into an area of just 12 square meters. Archaeologists think the bodies landed or were dumped in shallow ponds, where the motion of the water mixed up bones from different individuals. By counting specific, singular bones — skulls and femurs, for example — UG forensic anthropologists Ute Brinker and Annemarie Schramm identified a minimum of 130 individuals, almost all of them men, most between the ages of 20 and 30.

The number suggests the scale of the battle. “We have 130 people, minimum, and five horses. And we’ve only opened 450 square meters. That’s 10% of the find layer, at most, maybe just 3% or 4%,” says Detlef Jantzen, chief archaeologist at MVDHP. “If we excavated the whole area, we might have 750 people. That’s incredible for the Bronze Age.” In what they admit are back-of-the-envelope estimates, he and Terberger argue that if one in five of the battle’s participants was killed and left on the battlefield, that could mean almost 4000 warriors took part in the fighting.

Tollense 2

What makes a life well-lived?

Friday, March 25th, 2016

What makes a life well-lived?

While traditionally the domain of priests, philosophers and novelists, in recent years survey researchers, economists, biologists and scientists have been tackling that question.

Kanazawa and Li theorize that the hunter-gatherer lifestyles of our ancient ancestors form the foundation for what make us happy now. “Situations and circumstances that would have increased our ancestors’ life satisfaction in the ancestral environment may still increase our life satisfaction today,” they write.

They use what they call “the savanna theory of happiness” to explain two main findings from an analysis of a large national survey (15,000 respondents) of adults aged 18 to 28.

First, they find that people who live in more densely populated areas tend to report less satisfaction with their life overall. “The higher the population density of the immediate environment, the less happy” the survey respondents said they were. Second, they find that the more social interactions with close friends a person has, the greater their self-reported happiness.

But there was one big exception. For more intelligent people, these correlations were diminished or even reversed.

“The effect of population density on life satisfaction was therefore more than twice as large for low-IQ individuals than for high-IQ individuals,” they found. And “more intelligent individuals were actually less satisfied with life if they socialized with their friends more frequently.”


If you’re smarter and more able to adapt to things, you may have an easier time reconciling your evolutionary predispositions with the modern world. So living in a high-population area may have a smaller effect on your overall well-being — that’s what Kanazawa and Li found in their survey analysis. Similarly, smarter people may be better-equipped to jettison that whole hunter-gatherer social network — especially if they’re pursuing some loftier ambition.

(Hat tip to P.D. Mangan.)

Intensely Territorial

Monday, March 21st, 2016

Humans and chimpanzees are intensely territorial, E.O. Wilson reminds us:

That is the apparent population control hardwired into their social systems. What the events were that occurred in the origin of the chimpanzee and human lines — before the chimpanzee-human split of 6 million years ago — can only be speculated. I believe that the evidence best fits the following sequence. The original limiting factor, which intensified with the introduction of group hunting for animal protein, was food. Territorial behavior evolved as a device to sequester the food supply. Expansive wars and annexation resulted in enlarged territories and favored genes that prescribe group cohesion, networking, and the formation of alliances.

For hundreds of millennia, the territorial imperative gave stability to the small, scattered communities of Homo sapiens, just as they do today in the small, scattered populations of surviving hunter-gatherers. During this long period, randomly spaced extremes in the environment alternately increased and decreased the population size so that it could be contained within territories. These demographic shocks led to forced emigration or aggressive expansion of territory size by conquest, or both together. They also raised the value of forming alliances outside of kin-based networks in order to subdue other neighboring groups.

Ten thousand years ago, at the dawn of the Neolithic era, the agricultural revolution began to yield vastly larger amounts of food from cultivated crops and livestock, allowing rapid growth in human populations. But that advance did not change human nature. People simply increased their numbers as fast as the rich new resources allowed. As food again inevitably became the limiting factor, they obeyed the territorial imperative. Their descendants have never changed. At the present time, we are still fundamentally the same as our hunter-gatherer ancestors, but with more food and larger territories. Region by region, recent studies show, the populations have approached a limit set by the supply of food and water. And so it has always been for every tribe, except for the brief periods after new lands were discovered and their indigenous inhabitants displaced or killed.

Questioning the Socratic Method

Saturday, March 19th, 2016

What happens when researchers question the Socratic method?

In a study published in the December 2011 issue of the journal Mind, Brain, and Education, four cognitive scientists from Argentina describe what happened when they asked contemporary high school and college students a series of questions identical to those posed by Socrates. In one of his most famous lessons, Socrates showed a young slave boy a square, then led him through a series of 50 questions intended to teach the boy how to draw a second square with an area twice as large as the first. Students in the 2011 experiment, led by researcher Andrea Goldin, gave answers astonishingly similar to those offered by Socrates’ pupil, even making the same mistakes he made. “Our results show that the Socratic dialogue is built on a strong intuition of human knowledge and reasoning which persists more than twenty-four centuries after its conception,” the researchers write. Their findings, Goldin and his co-authors add, demonstrate the existence of “human cognitive universals traversing time and cultures.”

But these “universals” come with a significant caveat. By the end of Socrates’ lesson, the Greek boy had figured out how to do the task. More than half of the contemporary subjects, on the other hand, failed to grasp the import of the philosopher’s 50 questions.

Why Do People See Ghosts?

Thursday, March 10th, 2016

Why do people see ghosts?

Psychologists refer to it as the “sensed presence.”

The sensed presence usually happens to individuals who have become isolated in an extreme or unusual environment, often when high levels of stress are involved. These individuals report a perception or feeling that another person is there to help them cope with a hazardous situation. The vividness of the presence can range from a vague feeling of being watched to a clearly perceived, seemingly flesh-and-blood entity such as Clooney’s character in Gravity. This entity might be a god, a spirit, an ancestor, or someone personally known to the observer. Sensed presences usually appear in environments with little variation in physical and social stimulation; low temperature is also a common ingredient.

Possible explanations for a sensed presence include the motion of boats, atmospheric or geomagnetic activity, and altered sensations and states of consciousness induced by changes in brain chemistry triggered by stress, lack of oxygen, monotonous stimulation, or a buildup of hormones. There is in fact exciting new evidence from a research group led by Olaf Blanke demonstrating that it is the precise stimulation of specific brain regions that tricks people into feeling the “presence” of a ghostly apparition.

Environmental psychologist Peter Suedfeld also thinks that what we do cognitively changes under these circumstances and may play a role.

Suedfeld proposed that we normally spend most of our time attending to and processing external, ambient stimuli from the physical world surrounding us. However, persistent exposure to stimuli that we are evolutionarily unprepared to process, or a lack of change in our surroundings, may cause us to focus more within ourselves, which most of us are much less experienced at doing.

Seeing ghosts may also be triggered by the “agency-detection mechanisms” proposed by evolutionary psychologists. These mechanisms evolved to protect us from harm at the hands of predators and enemies. If you are walking down a dark city street and hear the sound of something moving in a dark alley, you will respond with a heightened level of arousal and sharply focused attention and behave as if there is a willful “agent” present who is about to do you harm. If it turns out to be just a gust of wind or a stray cat, you lose little by overreacting, but if you fail to activate the alarm response and a true threat is present, the cost of your miscalculation could be high. Thus, we evolved to err on the side of detecting threats in such ambiguous situations. A recent study by Kirsten Barnes & Nicholas Gibson (2013) explored the differences between individuals who have never had a paranormal experience and those who have. They confirmed that experiences of supernatural phenomena are most likely to occur in threatening or ambiguous environments, and they also found that those who had paranormal experiences scored higher on scales measuring empathy and a tendency to become deeply absorbed in one’s own subjective experience.

Most likely, the experience of the sensed presence is the result of many of these factors interacting at once.

T-Cell Therapy

Tuesday, February 16th, 2016

Cancer researchers claim extraordinary results using T-cell therapy:

In one study, 94% of participants with acute lymphoblastic leukaemia (ALL) saw symptoms vanish completely. Patients with other blood cancers had response rates greater than 80%, and more than half experienced complete remission.


To administer the T-cell therapy, doctors remove immune cells from patients, tagging them with “receptor” molecules that target a specific cancer, as other T-cells target the flu or infections. They then infuse the cells back in the body.


T-cell therapy is often considered an option of last resort because reprogramming the immune system can come with dangerous side-effects, including cytokine release syndrome (sCRS) — and overload defense cells. Twenty patients suffered symptoms of fever, hypotension and neurotoxicity due to sCRS, and two died, but the researchers noted that chemotherapy had failed in all the patients who participated in the new trials.

When Liberals Attack Social Science

Saturday, February 13th, 2016

Jesse Singal left his copy of Galileo’s Middle Finger lying around the house when he went home for Thanksgiving, and his dad picked it up:

“That’s an amazing book so far,” I said. “It’s about the politicization of science.” “Oh,” my dad responded. “You mean like Republicans and climate change?”

Not exactly:

What she found, over and over, was that researchers whose conclusions didn’t line up with politically correct orthodoxies — whether the orthodoxy in question involved sexual abuse, transgender issues, or whatever else — often faced dire, career-threatening consequences simply for doing their jobs.

Two examples stand out as particularly egregious cases in which solid social science was attacked in the name of progressive causes. The first involves Napoleon Chagnon, an extremely influential anthropologist who dedicated years of his life to understanding and living among the Yanomamö, an indigenous tribe situated in the Amazon rain forest on the Brazil-Venezuela border — there are a million copies of his 1968 book Yanomamö: The Fierce People in print, and it’s viewed by many as an ethnographic classic. Chagnon made ideological enemies along the way; for one thing, he has long believed that human behavior and culture can be partially explained by evolution, which in some circles has been a frowned-upon idea. Perhaps more important, he has never sentimentalized his subjects, and his portrayal of the Yanomamö included, as Dreger writes, “males fighting violently over fertile females, domestic brutality, ritualized drug use, and ecological indifference.” Dreger suggests that Chagnon’s reputation as a careful, dedicated scholar didn’t matter to his critics — what mattered was that his version of the Yanomamö was “Not your standard liberal image of the unjustly oppressed, naturally peaceful, environmentally gentle rain-forest Indian family.”

In 2000, Chagnon’s critics seized upon a once-in-a-career opportunity to go after him. That was the year a journalist named Patrick Tierney published Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon. The book — and a related New Yorker article by Tierney — leveled a series of spectacular allegations against Chagnon and James V. Neel Sr., a geneticist and physician with whom Chagnon had collaborated during his work with the Yanomamö (Neel died of cancer shortly before the book’s publication). Among other things, Tierney charged that Chagnon and Neel had intentionally used a faulty vaccine to infect the Yanomamö with measles so as to test Nazi-esque eugenics theories, and that one or both men had manipulated data, started wars on purpose, paid tribespeople to kill one another, and “purposefully with[held] medical care while experimental subjects died from the allegedly vaccine-induced measles,” as Dreger writes.

These charges stuck in part because Terence Turner and Leslie Sponsel, two anthropologists who disliked Chagnon and his work, sent the American Anthropological Association an alarming letter about Tierney’s allegations prior to the publication of Darkness in El Dorado. Rather than wait to see if the spectacular claims in the book passed the smell test, the AAA responded by quickly launching a full investigation in the form of the so-called El Dorado Task Force — a move that led to a number of its members resigning in protest. A media firestorm engulfed Chagnon — “Scientist ‘killed Amazon indians to test race theory’,” read a Guardian headline — and he was forced to defend himself against accusations that he had brutalized members of a tribe he had devoted his career to living with and studying and, naturally, had developed a strong sense of affection for in the process. A number of fellow anthropologists and professional organizations came to the defense of Chagnon and Neel, pointing out obvious problems with Tierney’s claims and timeline, but these voices were drowned out by the hysteria over the evil, murderous anthropologist and his doctor-accomplice. Dreger writes that Chagnon’s “career had essentially been halted by the whole mess.” (Chagnon’s memoirs, published in 2013, are entitled Noble Savages: My Life Among Two Dangerous Tribes — the Yanomamö and the Anthropologists.)

There was, it turns out, nothing to these claims. Over the course of a year of research and interviews with 40 people involved in the controversy in one way or another, Dreger discovered the disturbing, outrageous degree to which the charges against Chagnon and Neel were fabricated — to the point where some of the numerous footnotes in Tierney’s book plainly didn’t support his own claims. All the explosive accusations about Nazi-like activities and exploitation, and the intentional fomenting of violence, were simply made up or willfully misinterpreted. Worse, some of them could have been easily debunked with just a tiny bit of research — in one case, it took Dreger all of an hour in an archive of Neel’s papers to find strong evidence refuting the claim that he helped intentionally infect the Yanomamö with measles (a claim that was independently debunked by others, anyway).

In the end, Dreger published the results of her investigation in the journal Human Nature, recounting the full details of Chagnon’s ordeal at the hands of Tierney, and the many ways Tierney fabricated and misrepresented data to attack the anthropologist and Neel. Darkness Is El Dorado is still available on Amazon, its original, glowing reviews and mention of its National Book Award nomination intact; and Tierney’s New Yorker article is still online, with no editor’s note explaining the factual inaccuracies contained therein.

A general intelligence factor in dogs

Thursday, February 11th, 2016

Researchers have confirmed that there is a general intelligence factor in dogs — some dogs are more equal than others:

Our results indicate that even within one breed of dog, where the sample was designed to have a relatively homogeneous background, there is variability in test scores. The phenotypic structure of cognitive abilities in dogs is similar to that found in people; a dog that is fast and accurate at one task has a propensity to be fast and accurate at another. It may seem obvious that once a detour task (finding the treat behind a barrier) has been solved in one form, the solution to the other forms will follow naturally, but dogs are not people. Experiments have shown that dogs’ problem-solving skills do not transfer readily from one problem to a different form of the same problem as ours do (Osthaus, Marlow, & Ducat, 2010). The g factor we report is consistent with the prediction made by the many experts in the ‘dog world’ (trainers, veterinarians, members of dog societies, and farmers) who were consulted in the early stages of this study. Those experts said that in their experience some dogs were more likely to catch-on, learn and solve problems more quickly than others. Our results show structural similarities between canine and human intelligence. Individual tests have some test-specific variance, tests are influenced by a group-level factor, and the group-level factor is influenced by a g factor. We tested models without the g factor, without the group-level factors and with uncorrelated group-level factors; models positing correlated group-level factors (the unstructured model and the hierarchical g model) fit the data. We emphasize the hierarchical g model because the poor fit of the no-g model rules out uncorrelated first-order factors; the hierarchical g allows us to examine how those correlations arise.

Although we cannot calculate empirically the impact of range-restriction (of intelligence) on our results we surmise that our sample of farm dogs is somewhat analogous to a human university student population because farm dogs at the low tail of the intelligence distribution are more likely to be given away as companion animals. Range restriction attenuates correlations (Alexander et al., 1984 and Wells and Fruchter, 1970) so we cautiously interpret the g factor we found as being a low estimate of commonality. A plot showing the possible impact on our results given various estimates of range restriction is given in the Supplementary Information together with the zero-order correlation matrix for all test scores.

Noise may arise from variation in appetite for treats. We assume that dogs vary in their appetitive motivation—and that differential interest in food treats may be confounded with test scores. Our finding that speed and accuracy are positively correlated suggests that this has not been a major concern, yet we expect that performance on a problem-solving test is affected by more than just ‘smarts’. Affective traits such as motivation, persistence, and so on likely influence performance on cognitive tasks, but if they contribute to covariance among tasks, it may be hard to distinguish these aspects from g; there is no a priori reason why g should not have an affective component. The crucial point is that our study investigates the covariance, the structure, among test scores. In humans where g has been most studied, g arises among mathematical and vocabulary tests even though students often have different preferences and motivation to do these kinds of tasks. If g tapped motivation heavily, we would expect to see covariance among measures of motivation across different kinds of test; in humans we do not see this (Loken, 2004).