At the heart of the racialist imaginary is the notion of the natural hierarchy of the races. Not only are there discrete types of humans, racialism insists, they are differentially endowed. Turn of the century high racialism construed this racial hierarchy in terms of a racial essence. This racial essence was supposed to control men’s character, merit, behavioral propensities, and capacity for refinement and civilization. To be sure, racial essence was thought of as multidimensional. But no educated Westerner at the turn of the century would beg to disagree with the notion that the races could be put into a natural hierarchy.

What explains the hold of high racialism on the turn of the century Western imaginary? Some of it was obviously self-congratulation. But that can’t be the whole story. There were some pretty smart people in the transatlantic world at the turn of the century. Why did they all find high racialism so compelling? Because critical thinkers interested in a question sooner or later find themselves sifting through the scientific literature, part of what needs explanation is the consensus on scientific racialism. Put another way, we should ask why the best-informed of the day bought into high racialism.

Broadly speaking, I think there were three factors at play. First, in the settler colonies and metropoles of the early modern world, migrant populations from far away found themselves living cheek-by-jowl with others. This created a visual reality of discrete variation out of what were in fact smoothly-varying morphologies. What were geographic clines reflecting morphological adaptation to the macroclimate in the Old World appeared to be races in the New World. In effect, early modern population history created a visual reality that begged to be described as a world of discrete races.

Second, and more important, was the weight of the taxonomic understanding of natural history. The hold of the taxonomic paradigm was so strong that it seemed to be the only way to comprehend the bewildering human variation revealed by the collision of the continents. The existence of specific races and their place in the natural hierarchy may be questioned but that racial taxonomy was a useful way to understand human variation was simply taken for granted. Unbeknownst to the best-informed of the day, this was a very strong assumption to make about the world.

Third, and most important, was the sheer weight of the explanandum. What made racial taxonomy so compelling was what it was mobilized to explain: the astonishing scale of global polarization. As Westerners contemplated the human condition at the turn of the century, the dominant fact that cried out for explanation was the highly uneven distribution of wealth and power on earth. It did really look like fate had thrust the responsibility of the world on Anglo-Saxon shoulders; that Europe and its offshoots were vastly more advanced, civilized and powerful that the rest of the world; that Oriental or Russian armies simply couldn’t put up a fight with a European great power; that six thousand Englishmen could rule over hundreds of millions of Indians without fear of getting their throats cut. The most compelling explanation was the most straightforward one. To the sharpest knives in the turn of the century drawer, what explained the polarization of the world was the natural hierarchy of the races.

It is this that distinguishes racialism from racism. The former is fundamentally an explanation of global polarization; the latter is a politico-ethical stance on the social and global order. In principle, it is possible to racialist without being racist but not vice-versa. In practice, however, few racialists could sustain politico-ethical neutrality on race relations.

During the nineteenth century, the discourse of Anglo-Saxon self-congratulation morphed from the traditional mode that saw Anglo-Saxons as blessed by Providence to the notion that they were biologically superior to all other races on earth. Driven by settler colonial racialism, the vision of the colorblind empire was definitely shelved by London in favor of a global racial order after the turn of the century. Things came to a head on the South Africa question where the settlers demanded apartheid. London gave in after a brief struggle. The resolution of the South Africa question in 1906 was a key moment in the articulation of the global color line.

The first real pushback against high racialism came from scholars at Columbia in the 1930s. Franz Boas and his students, most prominently Ruth Benedict, led the charge. They punctured the unchallenged monopoly of high racialism but the larger edifice survived into the Second World War. The discourse of high racialism collided with reality at the hinge of the twentieth century. As Operation Barbarossa began, Western statesman and intelligence agencies without exception expected the Soviet Union to collapse under the German onslaught in a matter of weeks. If France capitulated in six weeks, how could the Slav be expected to stand up to the Teuton for much longer? That the Slav could defeat the Teuton was practically unthinkable in the high racialist imaginary. Not only did the Soviet Union not collapse, it went on to single-handedly crush what was regarded as the greatest army the world had ever seen. This was because Stalinism proved to be a superior machine civilization than Hitlerism where it mattered—where it has always mattered to the West—on the battlefield. The Slav could indeed defeat the Teuton. The evidence from the battlefield required an unthinkable revision of the natural hierarchy of the races, directly antithetical to the core of the racialist imaginary, ie Germanic racial supremacism.

It would seem that Auschwitz, that great trauma of modernity, more than anything else pushed racialism beyond the pale. If so, it took surprisingly long. It was not until the sixties that racial taxonomy became unacceptable in the scientific discourse. Recall that it was in 1962 that Coon was booed and jeered at the annual meeting of the American Association of Physical Anthropologists, an association that had until quite recently been the real home of American scientific racialism. The anti-systemic turn of the sixties opened the floodgates to radical critiques of the mid-century social order and the attendant conceptual baggage, including a still-pervasive racialism.

It took decades before racialism was pushed beyond the boundaries of acceptable discourse. But by the end of the century a definite discipline came to be exercised in Western public spheres. In the Ivory Tower, a consensus had emerged that races did not reflect biological reality but were rather social constructs with all-too-often violent consequences. Whatever systematic differences that did exist between populations were considered to be trivial and/or irrelevant to understanding the social order. This consensus continues to hold the center even though it is fraying at the margins.

In fact, one can date the rise of neoracialism quite precisely. This was the publication of Murray and Herrnstein’s The Bell Curve in 1994. Although most of the book examined intelligence test scores exclusively for non-Hispanic White Americans and explored the implications of relentless cognitive sorting on the social order, critics jumped on the single chapter that replicated known results on racial differences in IQ. (Responding to the hullabaloo the American Psychological Association came out with a factbook on intelligence that was largely consistent with the main empirical claims of the book.) Herrnstein passed away around the time when the book came out. But, ever since then, Murray has been hounded by protestors every time he makes a public appearance. At Middlebury College last year, a mob attacked Murray and his interviewer, Professor Allison Stanger, who suffered a concussion after someone grabbed her hair and twisted her neck. I think we must see this aggressive policing of the Overton Window (the boundary of the acceptable discourse) as the defining condition of what I call neoracialism. It is above all a counter-discourse. Those espousing these ideas feel themselves to be under siege; as indeed they are.

Neoracialism retains the taxonomic paradigm of high racialism but it is not simply the reemergence of high racialism. For neoracialism is tied to two hegemonic ideas of the present that were nonexistent back when high racialism had the field to itself.

The first of these is the fetishization of IQ. The test score is not simply seen as a predictor of academic performance, for which there is ample evidence. (For the evidence from the international cross-section see Figure 1). It is seen much more expansively as a test of overall merit; as if humans were motor-engines and the tests were measuring horsepower. The fetish is near-universal in Western society; right up there with salary, the size of the house, and financial net worth. It is an impoverished view of man, sidelining arguably more important aspects of the human character: passion, curiosity, compassion, integrity, honesty, fair-mindedness, civility, and so on.

Figure 2. Source: Lynn and Meisenberg (2017).

The second hegemonic idea is the blind acceptance of the reductionist paradigm. Basically, behavior is reduced to biology and biology to genetics. Both are dangerous fallacies. The first reduction is laughable in light of what may be called the first fundamental theorem of paleoanthropology: What defines modern humans is behavioral plasticity, versatility, and dynamism untethered to human biology. In other words, modern humans are modern precisely in as much as their behavior is not predictable by biology.

The reduction of biology to genetics is equally nonsensical in light of what may be called the first fundamental theorem of epigenetics: Phenotypic variation cannot be reduced to genetics, and indeed, even the environment. For even after controlling for both there is substantial biological variation left unexplained. Not only is there substantial phenotypic variation among monozygotic twins (those who have identical genomes), even genetically-cloned microbes cultured in identical environments display significant phenotypic variation. The only way to make sense of this is to posit that subtle stochastic factors perturb the expression of the blueprint contained in DNA even under identical environmental conditions. This makes mincemeat out of the already philosophically-tenuous paradigm of reductionism.

So neoracialism is a counter-discourse in contemporary history that is rigidly in the grip of the three fallacies: that racial taxonomy gives us a good handle on human variation, that IQ is the master variable of modern society and the prime metric of social worth, and that DNA is the controlling code of the human lifeworld à la Dawkins. Because the last two are much more broadly shared across Western society, including much of the Left, the critique of neoracialism has been relatively ineffective.

But beyond the rigidities of the contemporary discourse, there is a bigger reason for the rise of neoracialism. Simply put, racialism was marginalized without replacement. The explanatory work that racialism was doing in making sense of the world was left undone. No alternate compelling explanation for global polarization was offered. Instead, under the banner of Modernization, population differences were simply assumed to be temporary and expected to vanish in short order under the onslaught of Progress. Indeed, even discussion of global polarization became vaguely racist and therefore unacceptable in polite company. With the nearly-uniform failure of the mid-century dream of Modernization, the door was thus left ajar for the resurrection of essentialist racial taxonomy to do the same explanatory work it had always performed. It is the absence of a scientific consensus on a broad explanatory frame for human polarization that is the key permissive condition for neoracialism.

A scientific consensus more powerful that neoracialism, based on thermoregulatory imperatives, is emerging that ties systematic morphological variation between contemporary populations to the Pleistocene paleoclimate on the one hand, and contemporary everyday living standards (nutrition, disease burdens, thermal burdens) on the other. Disentangling the two has been my obsession for a while. I finally found what those in the know already knew. Basic parameters of the human skeleton are adapted to the paleoclimate.

At the same time as these developments in paleoanthropology and economic history, recent progress in ancient-DNA research has highlighted the importance of population history. I tried to bring the paleoanthropology and population history literature into conversation by showing how population history explains European skeletal morphology over the past thirty thousand years. My argument is based on known facts about the paleoclimate during the Late Pleistocene and known facts about population history. The paleoclimate is the structure and population history is the dynamic variable. It is that which allows us to predict dynamics in Late Pleistocene body size variables. We were of course forced into this explanatory strategy by the brute fact that population history and the paleoclimate are the main explanatory variables available for the Pleistocene.

I do not mean to imply that technology and organization did not causally affect human morphology, eg we have ample evidence of bilateral asymmetry in arm length as an adaptation to the spear-thrower. But all such adaptations are superstructure over the basic structure of human skeleton that reflects morphological adaptation to the paleoclimate of the Pleistocene that began 2.6 Ma. In Eurasia in particular, it reflects adaptation to the macroclimate after the dispersal of Anatomically Modern Humans from Africa 130-50 Ka. Because the Late Pleistocene, 130-10 Ka, is so long compared to the length of time since the Secondary Products Revolution 5 Ka, and especially the Secondary Industrial Revolution 0.1 Ka, and despite the possibility that evolution may have accelerated in the historical era, the Late Pleistocene dominates the slowest-moving variables of the human skeleton. Indeed, I have shown that pelvic bone width and femur head diameter reflect adaptation to the paleoclimate of the region where the population spent the Late Pleistocene.

I feel that economic historians have been barking up the wrong tree. The basic problem with almost all narratives of the Great Divergence (as the historians frame it) or the exit from the Malthusian Trap (as the economists would have it) is that the British Industrial Revolution, 1760-1830, does not revolutionize everyday living standards in England. This is easy to demonstrate empirically whether one relies on per capita income, stature, or life expectancy. In general, the economic, anthropometric, and actuarial data is consistent with a very late exit from the Malthusian world; the hockey stick is a story of the 20th century.

The evidence is rather consistent with the hypothesis that the extraordinary polarization of living standards across the globe is a function of the differential spread of the secondary industrial revolution, 1870-1970, (senso stricto: the generalized application of powered machinery to work on farms, factory floors, construction sites, shipping, and so on; senso lato: the application of science and technology to the general problem of production and reproduction). So proximately, what needs to be explained is the spread of the secondary industrial revolution. Specifically, the main explanandum is this: Why is there a significant gradient of output per worker (and hence per capita income) along latitude? Why can’t tropical nations simply import the machinery necessary to increase their productivity to within the ballpark of temperate industrial nations and thereby corner the bulk of global production? Despite the wage bonus and the ‘second unbundling’, global production has failed to rebalance to the tropics. Why??

I proposed a simple framework that tied output per worker to the rate of intensity of the work performed on the same machine; and the rate of intensity of work performed to the thermal environment of the farm, factory floor, construction site, dockyard and so on—in accordance with the human thermal balance equation. This was not very original—the claim is consistent with known results in the physiological and ergonomics literature. What I am saying in effect is that the difference is not so much biology, education, or culture. To put it bluntly, educated and disciplined male, White, Anglo-Saxon workers from the MidWest would not be able to sustain the intensity of work performed on the same machine at the same rate in Bangladesh as in Illinois. Like the Bangladeshis, they would have to take frequent breaks and work less so as not to overheat. This mechanically translates into lower productivity and hence lower per capita income.

I appreciate the increasing attention to thermal burdens in light of global warming. Recently, Upshot had a fascinating report tying gun violence outdoors but not indoors (!!!) to temperature spikes. Earlier, in an extraordinary study, Harvard’s Goodman tied students’ test scores to the thermal burden on the day of the test. That goes some way towards explaining the gradient of latitude in the international cross-section of test scores—an uncomfortable empirical fact well outside the Overton Window that neoracialists insistently point to as empirical “proof” of the relevance of racial taxonomy to understanding the global order. We’ll return to the empirical evidence from the correlates of test scores presently.

Following in the footsteps of Murray and Herrnstein, Richard Lynn published The Global Bell Curve in 2008. It went to the heart of the matter. Here, global polarization is tied precisely to test scores. Some populations are rich and powerful, and others are poor and weak because, we are told, the former are cognitively more endowed than the latter. That’s the master narrative offered here. One finds different versions in other neoracialist accounts. Rushton claimed racial differences in cranial capacity, that we debunked. Wade finds racial taxonomy more persuasive than the geographic clines favored by geneticists. In what he calls his more speculative chapters, Wade does the full double reduction: differences in behavioral patterns are mobilized to explain the world order and DNA is mobilized to explain behavioral patterns. Gene-culture coevolution and other speculations are thrown around to explain global polarization.

The heart of neoracialism isn’t, What’s the controlling variable for human variation per se. The question at the heart of neoracialism is, What’s the controlling variable for human variation that is relevant to the social order, the global order, the manifest and multiple hierarchies of our lifeworld? A presumed innate hierarchy of the races in general ability is doing all the work in neoracialism for it is mobilized to explain all of global polarization in one fell swoop. Neoracialism looks for a master variable that explains the presumed rank ordering of human societies. Whence the fetishization of IQ (thought to be ultimately controlled by DNA, although all efforts to explain test scores by DNA have been frustrated). In the minds of neoracialists and those who are tempted to join them, it is test scores that explain the cross-section of per capita income. A lot is thus at stake in that equation. That’s the context of Lynn’s The Global Bell Curve.

The rigidities of the liberal discourse have meant that a very fruitful way of thinking about systematic variation in the test scores of human populations have been overlooked. We argue that test scores contain information on everyday living standards. Put simply, they are a substitute for per capita income, stature, or life expectancy. They measure net nutritional status which is a function of nutritional intake and expenditure on thermoregulation, work, and fighting disease. (Net nutritional status is just jargon for the vicious feedback loop between nutrition and disease; they must be considered jointly.) We show this by showing that the best predictors of test scores are the Infant Mortality Rate and animal protein (dairy, eggs and meat) intake. More generally, we show that all metrics of net nutritional status are strong predictors of test scores.

While it may be conceivable that variation in cognitive ability explains variation in per capita income, given the universal availability of modern medicine, the claim that variation in cognitive ability explains variation in the Infant Mortality Rate is really tenuous. Given the empirical correlation we document below, it is much more plausible that tropical disease burdens suppress test scores than vice-versa. In other words, it makes no sense to infer that the racial hierarchy supposedly revealed by test scores explains disease burdens, but it make ample sense to infer that disease burdens explain test scores. This is the crucial wedge of our intervention.

We begin our empirical analysis by noting the Heliocentric pattern of test scores. Table 1 displays Spearman’s rank correlation coefficients for test scores on the one hand and absolute latitude and Effective Temperatures on the other. Spearman’s coefficient is a distribution-free, robust estimator of the population correlation coefficient (r) and more powerful than Pearson’s coefficient. Effective Temperature is computed from maximum and minimum monthly averages via the formula in Binford (2001): ET=(18*max-10*min)./(max-min+8), where the max and min temperatures are expressed in Celsius. ET is meant to capture the basic thermal parameter of the macroclimate.

Note that Effective Temperature is just a function of absolute latitude (r=-0.949, p<0.001). Our estimate of the correlation coefficient between absolute latitude and measured IQ test scores is large and significant (r=0.654, p<0.001), implying a gradient so large that moving 10 degrees away from the equator increases expected test scores by 4 points. Effective Temperature is also a strong correlate of measured IQ (r=-0.639, p<0.001), implying that an increase in Effective Temperature by just 5 degrees reduces expected test scores by 11 points. The fundamental question for psychometry then is, What explains these gradients?

Answering this question requires pinning down the proximate causal structure of test scores. We argue that test scores measure net nutritional status. Table 2 marshals the evidence. We see that all measures of net nutritional status (Infant Mortality Rate, animal protein intake per capita, life expectancy, stature, protein intake per capita, and calorie intake per capita) are strong correlates of test scores. The strongest is Infant Mortality Rate (r=-0.859, p<0.001) which captures the vicious feedback-loop between nutrition and disease burdens. By itself, Infant Mortality Rate explains three-fourths of the variation in measured test scores reported by Lynn and Meisenberg (2017). The results are robust to using estimated test scores or Educational Attainment instead of measured test scores.

Figure 2. Infant mortality rate (World Bank, 2014) predicts test scores (Lynn and Meisenberg, 2017).

Our estimate for the correlation between animal protein intake per capita and measured test scores is also extremely large (r=0.802, p<0.001). Astonishingly, each additional gram of animal protein intake per capita increases expected test scores by 0.4 points. By itself, animal protein intake explains two-thirds of the international variation in mean test scores. Although not as strong, calorie intake per capita (r=0.541, p<0.001) and protein intake per capita (r=0.649, p<0.001) are also strong correlates of test scores. The pattern suggests that the lower test scores of poor countries reflect lack of access to high-quality foods like eggs, dairy and meat.

Figure 3. Animal protein (FAO, 2018) predicts test scores (Lynn and Meisenberg, 2017).

The main import of the extremely high correlations between test scores on the one hand and Infant Mortality Rate (r=-0.859, p<0.001) and per capita protein intake (r=0.802, p<0.001) on the other is clear: Health insults control investment in cognitive ability. Energy and nutrition that could be channeled towards cognitive ability have to be diverted to dealing with health insults arising jointly from malnutrition and disease.

We have checked that stature is much more plastic than pelvic bone width. And we have shown that the divergence in stature is a story of the 20th century, ie it carries information of modern polarization. The strong correlation between test scores and stature (r=0.760, p<0.001) therefore suggests that test scores also contain information on modern polarization. The strength of the correlation between test scores and life expectancy (r=0.761, p<0.001) reinforces this interpretation.

Source: Lynn and Meisenberg (2017), Clio Infra (2018).

What Table 2 shows is that systematic variation in test scores between populations is a function of systematic variation in net nutritional status. The correlations make no sense if neoracialism is approximately correct, but they make ample sense if test scores reflect net nutritional status. If a country has low test scores you can be somewhat confident that it is poor (R^2=44%) but you can be much more confident that it faces malnutrition (R^2=64%) and especially high disease burdens (R^2=74%). This implies that the causal vector points the other way, from polarization to test scores. Far from explaining global polarization as in the high racialist imaginary, test scores are explained by inequalities in everyday living standards. The evidence from psychometry adds to other evidence of global polarization from economics, anthropometry, and demography that continues to demand explanation.

We have suggested that the current radio silence over systematic variation in test scores fosters neoracialism. We must break this silence and talk openly and honestly about such questions lest we leave the interpretation of these patterns to neoracialists. More generally, an effective rebuttal of neoracialism requires a more compelling explanation of global polarization. Given the discursive hegemony of science, I want to persuade progressives that this requires taking science as the point of departure. My wager is that a much more compelling picture is indeed emerging from the science itself that explains global polarization, and more generally, systematic variation in human morphology and performance, not in terms of racial taxonomy but rather in terms of the Heliocentric geometry of our lifeworld that structures thermoregulatory, metabolic, and epidemiological imperatives faced by situated populations.

In a contemplative article, Bernard Wood, the doyen of hominin taxonomy, identified three boundary problems in the business. The first is, of course, where to draw the line between ape and man; more precisely, the boundary between “ape-like” hominid and man-like hominin fossils. [Hominid includes the great apes; hominin does not.] It is not simply a matter of lineage for there are many species (by which we simply mean morphological types or taxa; not the biological definition—the ability to produce fertile offspring—which cannot be determined on the basis of extant evidence) in the fossil record that are neither the ancestors of modern humans nor that of modern chimps. So the question is above all where to place these dead-ends. In practice, the boundary is fuzzy and boils down to the degree to which the species is arboreal (adapted to living in the canopy) or bipedal. Committed bipeds are regarded as closer to modern humans; committed arboreals as closer to apes; with fossils displaying both adaptations somewhere in between.

Source: Wood and Collard (1999).

The second is the boundary of the genus Homo. Drawing this boundary is an equally fraught enterprise for now we are talking about demarcating which species can be regarded as human senso lato (in a loose sense). Committed bipedalism is not enough, it is reasonable to demand that species in our genus approach the human form if not behavior. Human-like behavior, especially tool manufacture, is of course enough to guarantee you a spot in the genus. But things are complicated due to the fact that multiple hominin species coexisted in eastern Africa when the first tools appear around 2.5 Ma (millions of years ago) so that it is impossible in general to attach the first industries to particular species. In practice, paleoanthropologists regard big brains as the ticket to entry with cranial capacity above 600 cubic centimeters (cc) regarded as the conventional boundary. The defining exception or marginal case is H. habilis (“handy man”, 2.5-1.4 Ma) which has definitely been tied to the first lithic technology but sports an average cranial capacity of only 552 cc. (Although Gamble reports an average of 609 cc. Compare figures 1 and 2.) We will presently return to encephalization in human evolution.

Source: Gamble (2013).

The third is the boundary between fully-human, H. sapiens senso stricto (in the strict sense), and near-human hominin. This is perhaps the most fraught boundary of the three. It is also uncomfortably close to the question of the origin of the races, that perennial obsession of high racialism. There is a virtual consensus that what distinguishes humans from other hominins is behavior—we are more sophisticated, behaviorally-plastic, and dynamic than those other guys. But this is very far from being free of problems. First, the appearance of anatomically modern humans considerably predates the evidence for behavioral modernity however defined, so that the origin of our species senso stricto is thereby shrouded in mystery. Second, some but not all late archaic hominins, in particular Neanderthals, are associated with advanced lithic technology (including Levallois tools) indistinguishable from contemporaneous anatomically modern humans (say around 100 Ka).

It would seem that there are two ways of resolving this boundary problem. Either we impose a less stringent criteria for behavioral modernity (say tool manufacture requiring multiple processes in a specific sequence) and therefore be generous with inclusion. Or we impose a more stringent criteria for behavioral modernity (say art, ornaments, burial, colonization of extreme environments, sea-faring, projectile weapons, and so on; in short, culture, versatility and dynamism) and be thereby stingy with inclusion. But both generous and stingy definitions are deeply-problematic.

For if you say advanced tool manufacture (say Acheulean tools c. 1 Ma, in particular, bifacial hand-axes) is sufficient criteria for inclusion then archaic hominin (including our ancestors) in the western Old World would be included but not those in eastern Eurasia for the spread of the Acheulean industry after 1 Ma was confined to west of the infamous but accurate Movius line. The eastern Old World, populated by late archaic hominins, continued to manufacture unsophisticated Oldowan tools developed c. 2.5 Ma for hundreds of thousands of years after Acheulean industry becomes dominant in the western Old World.

Source: Lycett and Bae (2010).

If on the other hand you say let’s be stingy and restrict H. sapiens senso stricto to much more recent hominin populations that display the full suite of modern behavior, then that would imply that populations in western Eurasia (Europe and the Near East) and Sahul (Australia, Tasmania, New Guinea) were fully-human by 50-40 Ka, tens of thousands of years before the rest of the world (say 20 Ka). No doubt this is extremely controversial. But the empirical evidence for global polarization in the Late Pleistocene is overwhelming. Basically, apart from some ephemeral early evidence in southern Africa around 90 Ka, the appearance of the full-package of behavioral modernity around 40 Ka is confined to western Eurasia to which the term Upper Paleolithic is properly applicable. To reach Sahul, of course, required sea-faring so that those populations were definitely fully-modern. A different term, Late Stone Age, applies to Africa from 50 Ka on. It is defined in terms of advanced lithic technology and does not sport evidence of the full-package of behavioral modernity. I’m walking on coals here … many Africanist prehistorians would be furious. But my goal is to problematize the modern-premodern dichotomy in prehistory.

My general point is that all three dichotomies are necessarily fuzzy. Any schema involving sharp boundaries in hominin taxonomy is guaranteed to be shot through with contradictions and glaring anomalies. In short, it’s a fool’s errand. In what follows we will not take a position on these boundary questions.

The title of the present dispatch is also a nod at another problem in narrative accounts of the human career. Namely, the temptation to take a teleological approach is very strong in this domain. ‘The Story of Man’ presumes that tracing how we got to where we are is a sufficient account of the hominin career. But that ignores the evolutionary dead-ends; more sympathetically, it ignores hominin forms and strategies different from ours that went out of business. The explosion of taxa is a testament to the extraordinary variation in hominin morphology (and therefore life history and survival strategy) that is not only interesting in itself, but also informs our own story. Just as a liberal order after the failure of Communism is quite different from the counterfactual without the Communist experiment, the story of us that emerges from a full consideration of alternative lifeways pursued by sister species is different and richer than a story that emerges from the tenuous assumption of telos in human evolution. In other words, we must tell the story of the others as well as of us because the story of the others informs the interpretation of our own story. What follows is a sketch of a broad-brush history of our tribe, the Hominini.

The story begins with the Planet of the Apes. During the Miocene, 23-5 Ma, the climate was much warmer and wetter. Siberia and Greenland were not glaciated and rainforests covered much of the Old World. Apes emerged out of Africa and colonized much of the Old World presumably jumping from canopy to canopy.

Source: Gamble (2013).

By the time of our last common ancestor with the chimps c. 7-6 Ma, it was still warm but the temperatures had fallen dramatically. Greenland was glaciated, the rainforests had receded, and apes had become confined again to Africa. This is where the first hominin began, very tentatively, to walk. The emergence of committed bipedalism was an excruciatingly slow process. Although we have scant fossil evidence for the period, it is clear that for millions of years, hominin refused to commit to bipedalism. They retained skeletal features like opposable toes that show that they were still arboreal and only occasional bipeds. Very little is known about early pre-australopith hominins c. 7-4 Ma other than they sport an ape-like morphology. Indeed, the only thing that distinguishes them from apes is that they were occasional bipeds. In fact, some experts suggest that they are too ape-like to be considered hominin. Regardless, one or more of these hominins, most likely from the genus Ardipithecus, evolved into Australopithecines, when things start to get really interesting.

Source: Liberman (2013).

Towards the end of the Pliocene, 5.3-2.6 Ma, the climate became much cooler. Rainforests disappeared from eastern Africa and Woodland and savannah expanded. A vast number of hominin taxa suddenly explode in the fossil record at this time. Most of them have been placed in the genus Australopithecus c. 4-1 Ma. The most famous australopith, of course, is Lucy (named after the Beatles’ song Lucy in the Sky with Diamonds) who lived in Ethiopia 3.2 Ma and belonged to the taxon A. afarensis. It is clear from her skeleton that Lucy was an obligate biped, eg the absence of opposable toes. But the earliest evidence for obligate bipedalism is from the Laetoli footprints made c. 3.6 Ma that have also been associated with A. afarensis.

There is no consensus on why bipedalism emerged at this time. Some have claimed that bipedalism might have been a postural adaptation with those able to stand upright being able to gather more fruit. Others have suggested that selection of bipedalism was due to the thermodynamic efficiency of bipedal locomotion in the expanding savannah or woodland habitats where sustenance was more sparsely distributed. Still others have emphasized the thermoregulatory advantage of upright walking. It has been suggested that australopiths engaged in midday scavenging when competition from quadruped scavengers (disadvantaged because they expose a much greater surface area to the sun) was absent or less intense. In all cases, the logic leads straight to the question of foraging strategy and therefore diet. We’ll return to this question shortly.

Australopiths, like all early hominin, had small bodies and small brains. Australopith females, for instance, were just 1.1m tall and weighed 28-35kg. Male Australopiths averaged 1.4m in stature and weighed in at 40-50kg. Thus, males were about 40-50 percent larger than females. From figure 2 we see that the index of sexual dimorphism for Australopiths (1.53) is closer to gorillas (1.68) than modern humans (1.16). This suggests that male Australopiths fought each other for access to females.

With an average cranial capacity of just 464 cc, their brains were nearly as small as that of modern chimps. Their brains were small not just in absolute volume but also relative to body mass. Indeed, their encephalization quotient comes to just 2.6, or less than half as much as modern humans who sport an EQ of around 6-7. Given their brain size, Dunbar’s social brain hypothesis suggests a network size of 67 individuals, less than half that of contemporary human population (136). They also had a much faster life history; taking about 12 years to reach adulthood.

Source: Liberman (2013).

While all early hominin were small-bodied and small-brained, they differed markedly in their dietary strategies. Both gracile Australopiths and robust Australopiths (the latter have recently secured their own genus, Paranthropus) ate a wide-variety of fruit, insects, leaves, tubers, roots, and the occasionally scavenged meat as attested by their greater molar size (compared to Ardipithecus). But what distinguishes the two is their masticatory (chewing) apparatus.

Source: Evans et al. (2016).

Taxa in the genus Paranthropus in general, and the taxon P. boisei in particular, were what Wood called megadonts. Their powerful masticatory muscles and very large molars allowed them to crush and grind hard foods such as nuts, seeds, roots, and tubers in the back of the jaw. Since the genus Homo emerged from the gracile Australopiths, the megadonts are the classic dead-end. None of their descendants survived. They vanish from the fossil record after 1.3 Ma. So the temptation is rather strong to see the roots of their doom in dietary specialization in hard-to-digest and poor quality foods. That temptation must be resisted. Microwear evidence from their tooth enamel suggests that their diets were just as varied as the gracile Australopiths. The decisive difference in dietary strategy between the two was in fallback foods, ie what they resorted to eating when their preferred food was unavailable. However, it is clear that their strategy did not generate the sort of feedback loop between foraging strategy, gut morphology, and encephalization that emerged in our lineage. That will be the subject of part II when we examine the career of the genus Homo. Stay tuned.

Source: Aiello and Wheeler (1995).

Christopher Ruff, a paleoanthropologist at the Johns Hopkins University School of Medicine and the director of the Center for Functional Anatomy and Evolution, has been very generous with his time. He has helped me greatly in refining my understanding on human morphology and our population history. Ruff and coworkers have recently published Skeletal variation and adaptation in Europeans: Upper Paleolithic to the Twentieth Century, 2018. The study examines a total of 2,179 individual skeletons since the Upper Paleolithic beginning 33 thousand of years ago (henceforth, Ka). He has been kind enough to share their data with me. What follows is based on my interrogation of this data in light of our population history.

The basics of west Eurasian population history are now well-understood. The following account is based on the scheme presented in David Reich’s Who We Are and How We Got Here, 2018. The picture that emerges from ancient-DNA studies is straightforward. Basically, there are three major departures in west Eurasian population history. (Here we focus specifically on Europe.) The first is the arrival of Homo sapiens during the early Upper Paleolithic around 40 Ka into a continent already populated by Neanderthals. H. sapiens had already mixed with Neanderthal populations in the Near East immediately upon their exit from Africa. There was further admixture in Europe.

Estimates of the precise degree of admixture are quite sensitive to assumptions about the neutrality of genomic sequences acquired from the Neanderthals since even genes acquired in a single admixture event could rapidly get fixed throughout the population if they come under selection; conversely, the prevalence of genomic sequences not under selection contains information on the degree of admixture. Almost all estimates however fall into single digits. This is perhaps not because mating was infrequent despite near-continuous contact but rather because of the large disparity in population sizes. The colonizers were dramatically more populous than the natives so that very high degree of mixing for the latter is consistent with low rates of mixing for the former. (Similar to interracial marriage rates in the present-day United States.)

By the Last Glacial Maximum 26 Ka, the Neanderthals had long vanished. It is not clear if they went extinct or were simply absorbed into H. sapiens populations. Upper Paleolithic populations of Europe were already morphologically-adapted to the macroclimate with more northern populations displaying bigger bodies in accordance with Bergmann’s Rule. This population is basically swamped by a second pulse around 9 Ka when the Neolithic Revolution generates a major population pulse of farmers in the central Eurasian region who explode out in both easterly and westerly directions. The former would go on to found the Dravidian-Harappan Civilization. In Europe, the hunter-gatherers survived in isolated pockets; especially at northern latitudes. Since the Neolithic farmers came from the Near East their morphology was adapted to the much warmer macroclimate of the central region. In accordance with Bergmann’s Rule, we expect them to be smaller than the more cold-adapted populations of the Upper Paleolithic. We’ll presently see what the data has to say about this.

A third major population pulse was triggered by the Secondary Products Revolution in the fourth millenium BCE. In the central region, this dramatic transformation in the material possibility frontier gives rise to the very first state society at Uruk. The introduction of these advanced technologies—especially the wagon, as David Antony has argued—from the core of the Uruk world-system to the periphery, in this case, north of the Caucasus, makes the systematic economic exploitation of the sparsely-endowed steppe possible for the first time. This material revolution in the hitherto very sparsely-populated steppe is in turn responsible for the ethnogenesis of the Yamnaya, the speakers of Proto-Indo-European (the mother tongue whose descendents are spoken by half the world’s population today).

Yamnaya pastoralists explode outward almost immediately from their homeland. By 5 Ka, a massive population pulse reaches Europe, another India, and a third the Altai mountains in Kazakhstan. The Yamnaya are an extremely violent and hierarchical rank-society; obsessed with martial glory, competitive feasting, and other male bonding rituals. They conquer the first-farmers of Europe and eventually the isolated pockets of hunter-gatherers (in particular, in Scandinavia). These migrations are extremely sex-biased. Yamnaya warrior-pastoralists likely took the women and slaughtered the men in raids and skirmishes as the horizon moved inexorably westward.

Source: David Reich (2018).

The end-result of this population history is that contemporary European populations are a sex-biased admixture of Pleistocene hunter-gatherers, Neolithic farmers, and Yamyaya pastoralists; in the reverse order in terms of weight in the population structure. These three populations were morphologically-adapted to very different macroclimates during the Late Pleistocene. Specifically, the first can be expected to be adapted to local conditions in Europe that were highly polarized by latitude (southern Europe was never glacial whereas northern Europe witnessed the massive glacial-interglacial whipsaw), the second to the considerably warmer conditions of the Late Pleistocene in the Near East, and the last, the Yamyaya, to the more-permanently glacial conditions of the Russian steppe. We thus expect systematic time-variation in European morphology consistent with this population history. More precisely, we expect the slower-moving morphological parameters (eg, pelvic bone width, femur head diameter) to fall after the invasion of the farmers from the central Eurasian region and rise after the invasion of the pastoralists from the Eurasian steppe.

Figure 1 and 2 display the pelvic bone width of the skeletons in the Ruff et al. (2018) dataset. We have resized the points by the number of skeletons in the dataset for given region and period. We have also merged some periods in the original dataset for simplicity. [Early Upper Paleolithic (33-26 Ka) and Late Upper Paleolithic (22-11 Ka) have been folded into Upper Paleolithic (33-11 Ka); Mesolithic (11-6 Ka) and Neolithic (7-4 Ka) into Neolithic (11-4 Ka); Bronze (4-3 Ka) and Iron/Roman (2.3-1.7 Ka) into Yamnaya (4-1.7 Ka); Early Medieval (c. 600-950) and Late Medieval (c. 1000-1450) into Medieval; and Early modern (c. 1500-1850) and Very recent (c. 1900-2000) into Modern (c. 1500-2000).]

Figure 1. Pelvic bone width in Europe, Men. Source: Ruff et al. (2018).

The evidence that emerges is pretty unambiguous. For both men and women there is a significant fall in pelvic bone width during the Neolithic transition, and a substantial rise contemporaneous with the Yamnaya transition. Since there was no major population replacement in the Medieval-Modern passage, the decline in body size cannot be traced to population history. Note the French outlier that attenuates the modern decline for women. Without the outlier, the modern decline in women’s pelvic bone width would be as significant as men’s.

Figure 1. Pelvic bone width in Europe, Women. Source: Ruff et al. (2018).

Similar results hold if we look at femur head diameter which is also strongly canalized (very slow-moving). Femur head diameter is the main weight-carrying parameter of the human body and as slow to change as pelvic bone width.

The length of the thigh bone (femur) is much more developmentally-plastic than either pelvic bone width of femur head diameter. Yet, we know that even femur length (and hence stature) exhibits morphological adaptation to the macroclimate. The evidence that emerges from this dataset is consistent with our previous findings.

Finally, for the sake of completeness, we include graphs for stature. These ought to be congruent with the results for femur length since the former is a linear function of the latter.

The evidence that emerges is consistent with the idea that population history confounds the interpretation of the time-variation (as opposed to the just the cross-section as we have argued until now) of morphological parameters of the human body. In order to make valid inferences, population history must be kept in mind.

I constructed an index of body size by adding up the z-scores of femur head diameter and pelvic bone width. It is a less noisy measure of body-size that those considered above. The overall pattern revealed by the Body-Size Index is very compelling. We observe that size falls in the Upper Paleolithic-Neolithic passage and rises with the arrival of the Yamnaya precisely as predicted by population history. The modern decline does not correspond to any major population movement and therefore cannot be explained by population history.

The decrease in body-size is consistent with other evidence of gracialization during the transition to modernity. Men have not only become smaller, even their faces have become less aggressive (not to speak of manners and behavior). Could it be that changing social norms against the warrior code rewarded variants with traits less associated with aggression with greater reproductive success? Or did the rewards for body-size decline with better technology for grunt work? We don’t know. There is certainly a case to be made for a general process of gracialization related to modernity.

P.S. On second thoughts, it may not be wise to combine sexes after all. There is good reason to think that women’s pelvic bone width is more plastic than men’s because maternal mortality can adjust the latter quite rapidly. The best measure we have is men’s pelvic bone width. Here I graph the mean pelvic bone width of European men without combining periods. The evidence is consistent with the population history noted above. The overall pattern suggests strong gracialization after the Last Glacial Maximum, a further fall in body-size with the arrival of Neolithic farmers, a dramatic rise with the arrival of Yamnaya pastoralists; followed by slow upward drift until the end of the Middle Ages, strong gracialization in the early modern period, and very partial restoration after c. 1900. The big question thrown up by the present investigation is of course the dramatic decline in European body-size after the Black Death. But the overall elephant shaped pattern is very interesting as well.