Richard Lynn famously spent a few decades collecting data on human intelligence around the world. Eventually, he was able to generate world maps of average intelligence levels by nations and the ethnic groups that comprise them. Since some patterns were quite evident in the data, e.g., people from near the equator were lower in intelligence compared to those further away, this lead to hypothesizing causes of this pattern. Most people are by now familiar with one model: cold winter’s theory. This theory was deleted from Wikipedia by communist activists in already back in 2016. The idea is that surviving the winter is difficult in areas with cold winters, so groups who migrated to such environments faced an increased selection for intelligence, planning ability and so on. At the equator, the earth does not have seasons, so there is no such thing as winter as a cold period of the year. But who actually come up with this model? Lynn, Rushton, someone else? Let’s try to trace the origins. Rushton is a useful starting point. In his 1995 book Race, evolution, and Behavior, he wrote:
Given an African origin of less than 200,000 years ago, a dispersal event out of Africa about 100,000 years ago, and a peopling of the rest of the world thereafter, the question arises as to how these events led to the behavioral profiles found among the races. Why would Mongoloids have ended up the most K-selected? I agree with those who have proposed that colonizing temperate and cold environments leads to increased cognitive demands to solve the problems of gathering food and gaining shelter and general survival in cold winters (e.g., Calvin, 1990; R. Lynn, 1987, 1991a).
- Calvin, W.H. (1990). The Ascent of Mind. New York: Bantam Books.
- Lynn, R. (1987). The intelligence of the Mongoloids: A psychometric, evolutionary and neurological theory. Personality and individual differences, 8(6), 813-844.
The book appears to be have been largely forgotten but it looks interesting enough to read. I can see that Razib Khan read it back in 2014, and awarded it a 4/5 rating on Goodreads.
The 1987 Lynn paper is the first explicit discussion of the climate model that I can find. The abstract reads:
This paper presents a theory of the intelligence of the Mongoloids consisting of three linked sub-theories. The first concerns the psychometric features of Mongoloid intelligence and proposes that Mongoloids are characterised by high general intelligence (Spearman’s g), high visuospatial abilities and low verbal abilities. Mongoloid abilities also display slow maturation in infancy and early childhood. It is proposed that this pattern of abilities cannot be explained in environmental terms and should be regarded as substantially genetically programmed. The second sub-theory presents an evolutionary explanation for this pattern of abilities in Mongoloids, whereby it is proposed that the extreme cold of the ice ages acted as a selection pressure for increases in Spearman’s g and the visuospatial abilities. The low verbal abilities and slow maturation rates are interpreted as by-products of these adaptations. The third sub-theory presents a neurological model for the Mongoloid brain in which it is proposed that cortex devoted to the visuospatial abilities was expanded at the expense of the cortex devoted to the verbal abilities. The implication that there exists a negative correlation between the visuospatial abilities and the verbal abilities is considered in the concluding part of the paper and shown to be correct.
Lynn states his overall model as this (long quote!):
Evolution of Spearman’s g in Mongoloids
By approximately 250,000 years ago Australopithecus had evolved into Homo sapiens, and had acquired strong general intelligence and good verbal and visuospatial abilities. The next stage of the evolutionary process took place about 120,000 years ago.
By this time Homo sapiens was well adapted to survival in Africa and some groups began to migrate northwards into Europe and Asia. Those who remained in Africa were the ancestors of the living Negroids who retained the dark skin that gave protection from strong sunlight and the peppercorn hair that reduced the rapid evaporation of sweat, protects the head from excessive heat and from sunstroke. Those who migrated northwards evolved the pale skins which enabled them to absorb vitamin D from sunlight. At this stage these pale skinned populations were a single undifferentiated race (Nei, 1978).
A further stage of this evolution occurred approximately 60,000 years ago. From this time the ice ages began to descend on the northern regions and their effects were particularly severe in North East Asia. The reasons for this were firstly that this region is such a large land mass and secondly that the Himalayas acted as a barrier in the south. The effect was that the populations in North East Asia found themselves boxed in between the encroaching ice from the Himalayas in the south and from the Arctic region in the north. The cold to which they were subjected in this region was far more severe than that experienced by the other pale skinned populations in Europe, who were relatively close to the sea and had no southern ice barrier equivalent to the Himalayas. It was in response to this extreme cold that these populations evolved their distinctive physical adaptations of the epicanthic fold and the slit eyes to afford protection against the cold and the glare of the sunlight on the snow, and the flattened face and shortened limbs to reduce heat loss (Coon, 1955; Bodmer and Cavalli-Sforza, 1976). These physical adaptations to extreme cold differentiated the Mongoloid race from the Caucasoids in Europe and the Middle East.
It is suggested that this hostile environment acted as a new environmental niche which exerted selection pressure for a further increase in intelligence. As Jerison has observed “it takes more brains to make a living in some niches than in others” (1982, p. 747), and if ever there was a niche in which it took brains to survive it was surely North East Asia during the ice ages. This was the coldest part of the world inhabited by early Homo sapiens. Even today temperatures of – 87°F have been recorded in Siberia, and this would have been just an average day for the Mongoloid people during the ice ages. To survive in these temperatures they would have had to construct shelters well insulated from the cold, to build fires, to make warm clothes, to store food and to plan ahead for the winters which were even colder than the summers. For all of these the selection pressure for improved general intelligence would have been stronger than for the Caucasoids and the Negroids. It is therefore proposed that this is the most probable explanation in evolutionary terms for the high general intelligence (Spearman’s g) of the Mongoloids.
Lynn leans on Jerison’s work which is this 1982 book chapter in one of those Robert Sternberg edited books:
- Jerison, H. J. (1982). The evolution of biological intelligence. Handbook of human intelligence, 723-791.
I couldn’t find a copy of this, please email me if you can find one. It’s cheap on Amazon. Rushton (1995) also cites works by Jerison, but cites these instead:
- Jerison, H. J. (1963). Interpreting the evolution of the brain. Human Biology, 35(3), 263-291.
- Jerison, H. J. (1973). Evolution of the Brain and Intelligence. New York: Academic
The second seems to be another largely forgotten book of historical interest.
What about the third reference, Lynn’s 1991 paper? In fact, the fall-winter issue of Mankind Quarterly was a special issue devoted to this topic. As far as I can tell, it was due to Lynn publishing his global review of intelligence differences in the spring issue in 1991. The full paper listing is:
- (Spring issue). Lynn, R. (1991). Race differences in intelligence: A global perspective. Mankind quarterly, 31(3), 255-296.
- Lynn, R. (1991). The evolution of racial differences in intelligence. Mankind Quarterly, 32(1), 109.
- Eysenck, H. J. (1991). Race and intelligence: An alternative hypothesis. Mankind Quarterly, 32(1), 133.
- Miller, E. M. (1991). Climate and intelligence. Mankind quarterly, 32(1), 137.
- Weiss, V. (1991). Why are Racial Differences in Intelligence not Larger?. Mankind Quarterly, 32(1), 143.
- Lehrl, S., Frank, S., & Papp, R. (1991). Overcoming the Limitations of IQ. Mankind Quarterly, 32(1), 147.
- Juhel, J. (1991). Has the Study of Racial Differences in Intelligence Overcome its Racist Origins?. Mankind Quarterly, 32(1), 151.
- Vancata, V. (1991). Race Differences in Intelligence: A Microevolutionary and Ecological Perspective. Mankind Quarterly, 32(1), 157.
- Deary, I. J. (1991). Pandora’s Box and the Eskimo’s Nose. Mankind Quarterly, 32(1), 163.
- Lynn, R. (1991). Reply to Commentaries on Racial Differences Intelligence. Mankind Quarterly, 32(1), 171.
In the paper, Lynn provides a summary of the principles outlined by Jerison:
General Principles of the Evolution of Intelligence
The general principles governing the evolution of intelligence have been established by Jerison (1973). He has shown that from time to time populations have moved into new niches which have entailed increased cognitive demands for survival. When this has occurred the populations have responded by evolving larger brains in relation to body size, i.e. larger “encephalisation quotients”. Larger brains have the capacity for greater intelligence and have enabled the populations to deal with the cognitive demands of the new niche.
There have been four major occasions in which the occupation of new niches led to the development of larger brains and, by inference, greater intelligence. The first was the evolution of mammals approximately 220 million years ago. These discovered the nocturnal niche in which they slept during the day and foraged at night and they developed larger brains to deal with the integration of visual, auditory and olfactory information. The second was the evolution of the birds approximately 160 million years ago. In this case the problems of pair bonding and co-opera- tive feeding of the young in nests required the development of greater intelligence and larger brains. The third was the evolution of primates approximately 60 million years ago. They became diurnal, occupied a tree living niche and developed as social animals and to deal with the problems of the new niche they again developed larger brains.
[summary of the other 3 major steps]
But these aren’t the first papers to discuss this topic, broadly speaking, in post-WW2 times. There is the significant Beals paper from 1984:
- Beals, K. L., Smith, C. L., Dodd, S. M., Angel, J. L., Armstrong, E., Blumenberg, B., … & Trinkaus, E. (1984). Brain size, cranial morphology, climate, and time machines [and comments and reply]. Current Anthropology, 25(3), 301-330.
A bioclimatic model is evaluated as an explanation of variation in cranial capacity among 122 ethnic groups. Distribution of absolute and relative endocranial volume is mapped. Significant correlations occur with all nine climatic variables examined. Major foci of adaptation occur with solar radiation, vapor pressure, and winter temperature. Global mean trait increase is 2.5 cm per degree of equatorial distance. The interactive geometry between cranial size and shape is described, with encephalization and brachycephalization considered as functionally connected trends. Breadth is the most important structural component determining capacity. Relations between body size and brain size indicate that human populations under severe cold stress obtain large volumes more from rounder cranial shape than from differentiation by total body size. A computerized mapping program is developed and applied to anthropometric, climatic, and HRAF files. Its potential to produce clinal depictions through the Pleistocene (“time machine project”) is discussed. Paleontological data are summarized for 147 hominids.
This paper did not discuss intelligence as measured by tests, but it did discuss brain size variation across the globe and its relations to climate, especially the winter cold:
To our knowledge, the first suggestion that such morphology is a reflection of thermoregulation was given by Coon (1955:296): “It is easier to keep a small head cool than a large one. Witness the extreme dolicocephaly of hot-country peoples. In regions of great cold a large head is at an advantage from this point of view, as is a round one.” From a geophysical perspective, the energy available to flora and fauna basically depends upon the earth’s inclination to the sun. As high-energy photons of solar radiation decrease, the body and cranium must become more energy-conserving. Innovations such as specialized tools and controlled use of fire permitted occupation of areas of lower solar radiation and thereby set in motion a series of physio- logical and anatomical changes. Such trends of ecotypic differentiation should be observable in the fossil record-at least since the first significant exposure to winter frost (approximately a half-million years ago).
This may appear as a rather strange model. The authors proposed that the brain size differences between races evolved due to temperature regulation, and not due to intelligence selection. This is bizarre because the evolution of human brain size in comparison to other species is obviously related to our species’ dominating intelligence, so why would one posit a new theory when it comes to subspecies (race) differences? One of the critics of the paper (Kathleen R. Gibson) pointed this strangeness out:
Nor does the postulate that brain size increased to conserve body energy make sense. The average human brain consumes 20% of the body’s metabolic energy. Much more metabolically effective ways of conserving heat would be the evolution of insulating layers of hair, fat, or clothing. In fact, the brain uses so much energy that extensive brain enlargement would be incompatible with survival in food-scarce environments unless it provided cognitive skills enabling increased foraging efficiency and/or increased cultural adaptation to harsh circumstances. The fact that a correlation between cognition and brain size has not been convincingly demonstrated does not mean it has been disproven. Most literature on this subject is either anecdotal or based on questionable brain-size and intelligence data. To answer this question in a scientifically valid fashion will require the development of accurate, culturally unbiased methods of determining both intelligence and brain size in healthy young adults. For now, the most logical explanation of brain expansion remains that the brain expanded because neural functions were selectively advantageous.
Beals et al rescue themselves in their reply:
We have no contribution to make toward understanding how the brain functions. It is true that 4,000 generations is theoretically sufficient time for selection to “iron out kinks and equalize intelligence.” The point is that no matter how many generations are involved, no sufficient evidence has ever been presented that variation in population brain size, head size, head shape, or cranial capacity has a connection to intelligence in the first place.
This illustrates the usual point that every minor step in the epistemic path to accepting the genetics of race and intelligence was avoided on any grounds one could think of. Intelligence is obviously related to brain size, but this was denied for many decades to avoid the undesired conclusions further down the epistemic road.
There are many later works that continue on the same thing (e.g. this GScholar query), here’s a non-exhaustive list:
- Lynn, R. (2003). The geography of intelligence. In The scientific study of general intelligence (pp. 127-146). Pergamon.
- Lynn, R. (2006). Race differences in intelligence: an evolutionary analysis. Washington Summit Publishers.
- Templer, D. I., & Arikawa, H. (2006). Temperature, skin color, per capita income, and IQ: An international perspective. Intelligence, 34(2), 121-139.
- Kanazawa, S. (2008). Temperature and evolutionary novelty as forces behind the evolution of general intelligence. Intelligence, 36(2), 99-108.
- Wicherts, J. M., Borsboom, D., & Dolan, C. V. (2010). Why national IQs do not support evolutionary theories of intelligence. Personality and individual differences, 48(2), 91-96.
- Grove, M. (2012). Orbital dynamics, environmental heterogeneity, and the evolution of the human brain. Intelligence, 40(5), 404-418.
- Kanazawa, S. (2012). The evolution of general intelligence. Personality and Individual Differences, 53(2), 90-93.
- Nyborg, H. (2013). Migratory selection for inversely related covariant T-, and IQ-Nexus traits: Testing the IQ/T-Geo-Climatic-Origin theory by the General Trait Covariance model. Personality and individual differences, 55(3), 267-272.
- Pesta, B. J., & Poznanski, P. J. (2014). Only in America: Cold Winters Theory, race, IQ and well-being. Intelligence, 46, 271-274.
- Templer, D. I., & Stephens, J. S. (2014). The relationship between IQ and climatic variables in African and Eurasian countries. Intelligence, 46, 169-178.
- Frost, P. (2019). The Original Industrial Revolution. Did Cold Winters Select for Cognitive Ability?. Psych, 1(1), 166-181.
- Andrade, G., & Campo Redondo, M. (2019). Rushton and Jensen’s Work has Parallels with Some Concepts of Race Awareness in Ancient Greece. Psych, 1(1), 391-402.
- Lynn, R. (2019). Reflections on sixty-eight years of research on race and intelligence. Psych, 1(1), 123-131.
- History from the man himself
- Winegard, B., Winegard, B., & Anomaly, J. (2020). Dodging Darwin: Race, evolution, and the hereditarian hypothesis. Personality and Individual Differences, 160, 109915.
- Figueredo, A. J., Hertler, S. C., & Peñaherrera-Aguirre, M. (2021). The biogeography of human diversity in cognitive ability. Evolutionary Psychological Science, 7(2), 106-123.
- Pesta, B. J., Fuerst, J., & Kirkegaard, E. O. W. (2021). County-level USA: No Robust Relationship between Geoclimatic Variables and Cognitive Ability. Geographical Research.
There’s also a large body of non-human research about climate (including winter survival), intelligence and brain size. It does not generally refer to the parallel human literature. I have reviewed some of this before in another post. I am sure there’s more here to be found. I suspect the best research can be done on birds because these vary widely in their habitats, have many subspecies, many of them do not migrate to avoid the winter (thus subject to selection for this factor), and there’s a lot of data because humans like bird watching.
It is also possible to do experimental studies in animals. One could begin with a large population of mice, separate them at random into large warehouses with artificially modified climates and the related food scarcity that is similar to the winter climate. As a matter of fact, one could simply let some of them survive in actual winters through foraging and so on, and another set survive in a warm climate with year-round easy foraging and no winter colds. Insofar as mice need to deal with the difficulty of winter survival, this should cause the winter-exposed group to evolve higher intelligence. Invasive species provide a natural experiment of this sort, and could be studied.
Based on my review of the historical writings, the first to explicitly connect human intelligence with cold winter weather is Richard Lynn in his 1987 and 1991 papers. Since then many have followed suit. It is possible that some of the older researchers, e.g. Carleton S. Coon, had this idea before. I am not familiar with their work and Lynn, Rushton etc. did not cite them, so if they wrote about it, it was probably not a big influence. Instead, the biggest early influence seems to have been the general principles set out by Harry J. Jerison (multiple works cited) for the evolution of brain size in land animals, mammals, apes, humans, and the systemic compilation of skulls by Beals et al in 1984. Adding these two together, one gets a climate theory of human race (subspecies) differences. The next step was to collect intelligence data to check if it fit the data, and the rest is history.