There has been continuous worldwide selection for intelligence, although its strength may have varied with climate. Intelligence gradually increased, as reflected in the sophistication of the human tool kits. This increase was caused by intelligence increasing mutations, followed by the spread of these mutations. These mutations occurred at approximately the same rate (per million population) on different continents, but in absolute number were most common in the Eurasian land mass with its high population. When Australia and the Americas were settled the original populations lacked certain alleles because the relevant mutations had not yet occurred, or because these mutations had not reached the relevant parts of Eurasia. After Australia and the Americas came to be isolated from the larger Eurasian populations, they did not receive further immigrants. Although, a few intelligence raising mutations occurred in their populations, the smaller Australian and American (Indian) populations implied that the total number of beneficial mutations was less than in Eurasia. Thus, the intelligence of the Australian and American aboriginal populations came to lag behind that of the rest of the world. The literature on Australian aboriginal intellectual performance is reviewed, being shown to be low as expected.
In his survey of the intelligence of the world's peoples Lynn (1991) found that the highest levels were found in people that evolved in Eurasia (Mongoloids and Caucasoids), while low values were found for those that evolved in Africa (Negroids), and among those from the Americas and Australasia. Most of the discussion of causes for this has focused on the differences between the three major races, with little attention paid to the Amerindians and the Australians.
Among the few who have tried to explain the evolution of racial differences in intelligence, the most common explanation has been climate. These theorists have argued that the intellectual demands of life in cold climates were greater than in warm climates. Lynn has placed emphasis on the intellectual abilities needed to survive cold, to build fires, and to hunt in groups. Miller (1991) has pointed to the need to store food to survive the winter and how this may have selected for intelligence. He has also emphasized the importance in cold climates of avoiding a mate who deceives promising continued provisioning that is not delivered, or accepting provisioning when the resulting children will not be those of the provisioning mate (Miller, 1995). Intelligence helps both in carrying out, and in detecting such detection. The implicit assumption in all such models of differential selection is that all populations had access to the genetic variation required for intelligence to evolve. Thus, intellectual differences between populations had to reflect differences in the strength of selection for intelligence.
The alternative to be presented here is that more of the mutations that led to high intelligence occurred on continents with large populations than on less populated continents (Australia and the Americas). The selective forces for intelligence were present on all continents, although quite possibly differing in strength. The continents where the most such mutations had occurred would have the highest average intelligence. With equal mutation rates throughout the world, the continental area experiencing the largest number of mutations would be Eurasia. The fewest would be experienced in Australia.
There are several stylized facts (well established generalizations) that will be used in the argument.
One view has focused on the external world, discussing factors such as tool use, hunting, gathering, throwing (Calvin, 1990), etc. This approach seems to have become less fashionable recently, possibly because environmental driven evolution would seem to imply that if the environments differed, the strength of selection for intelligence would differ. Since environments obviously differ, populations might differ in intelligence. This conclusion is unacceptable to many, although others have considered the possibility of this happening in response to climatic differences (Miller 1991, Lynn 1991).
Others have emphasized the selective pressures for greater intelligence that can be created by humans interacting among themselves. Alexander (1990) has emphasized competition among individuals, and the need to outwit ones fellow men.
Buss (1994, p. 34) reports that in a survey of 10,047 people in 37 nations concerning desirable traits in a mate, women ranked intelligence fifth out of eighteen traits. In a smaller list of thirteen desirable characteristics, intelligence emerges in second place worldwide. In ten cultures women ranked intelligence higher than men did. However, in the other 27 countries both sexes placed an equally high premium on intelligence.
It is not hard to explain why this preference for intelligent mates exists. According to Buss (1994, p. 34), "these are likely to include good parenting skills, capacity for cultural knowledge, and adeptness at parenting. In addition, intelligence is linked with oral fluency, ability to influence other members of a group, prescience in forecasting danger, and judgment in applying health remedies. Beyond these specific qualities, intelligence convey the ability to solve problems." Of course, in modern industrial societies, intelligence is correlated with socioeconomic status (Herrnstein & Murray, 1994; Itzkoff, 1994), and "in tribal societies the head men or leaders are inevitably among the most intelligent in the group." (Buss, 1994, p. 34). Of course, the leaders of a group usually have greater access to fertile females and the resources to raise them.
Buss (1994) also emphasizes how in human mating deception is often used. Men try to convince women that they have, or will have resources, and will devote them to the well-being of a particular woman and her children (and not squander them on other women and their children), while women try to convince men that they will be sexually faithful to them (while possibly seeking better genes from other men). Buss states (p. 155), "Because the deceived can suffer tremendous losses, there must have been great selection pressures for the evolution of a form of psychological vigilance to detect cues to deception and to prevent its occurrence. The modern generation is merely one more cycle in the endless spiral of an evolutionary arms race between deception perpetuated by one sex and detection accomplished by the other. As the deceptive tactics get more subtle, the ability to penetrate deception become more refined."
Miller (1995) has argued that the above selective pressures would be strongest in cold climates. In such climates, male provisioning is critical for surviving the winter. Males have an incentive to deceive females as to their long term reliability. Females use intelligence to deceive males as to their sexual faithfulness, and the paternity of their children. Both sexes are under strong selection for the intelligence required to avoid being deceived. In the tropics, where females can support themselves, the selective pressures for intelligence are not as strong.
Wills (1993) has emphasized also a possible role for sexual selection, titling one of his books The Runaway Brain. Once mates came to be selected on the basis of intelligence, or something produced by it (such as musical or conversational ability) there would have been unidirectional selection for intelligence with the most intelligent individuals having the best access to mates, and leaving more descendants.
It will be presumed that each individual has a equal probability of experiencing an intelligence raising mutation (regardless of the population they live in). This is standard genetic theory, since no population differences in vulnerability to mutations are known. Weakening this assumption would not change the nature of the argument.
There is evidence from archaeology that human intelligence has been steadily increasing.
The material culture of prehistoric man was at a very low level before the emergence of anatomically modern man, and gradually increased. The rate of progress was very slow. There were periods of tens of thousands to hundreds of thousands of years when the tool kits used by primitive hominids remained essentially constant.
This slow rate of progress is more consistent with biological evolution than with cultural evolution. If the populations had been similar to current populations in ability, it is likely that better methods would have been quickly discovered and adopted. The best way to explain the failure to discover and to adopt more sophisticated tools is that the population had not yet acquired the intellectual abilities needed to develop and use these methods.
A quick history of stone technology may be useful. Because organic material perishes, most of our evidence of early human intellectual achievements consists of the stone tools they left behind. The earliest tools are the Oldowan, which were extremely crude scrapers, choppers, and flakes, each being the product of a few strokes with a hammerstone, and are dated at about 2.5 million years ago. This persisted for about a million years. It was followed by the Acheulian industry, which represented only a modest advance. However, this did represent "the first tool in which a predetermined shape has been imposed on a piece of raw material" (Lewin, 1989, p. 114). The hand ax, which was characteristic of this technology involved two converging sharp edges, which "required the shape to be seen within the lump of stone, which is then worked toward with a series of careful striking actions," (Lewin, 1989, p. 114). Constructing such "esthetically pleasing products of hours of skilled labor" probably required more intelligence than merely knocking two stones together.
Once developed the Acheulian technology persisted for over a million years. The most plausible explanation for the failure to adopt more sophisticated techniques is that the population lacked the intellectual ability to conceive of and adopt these techniques. If the population had the ability required to use a more sophisticated technology, surely it would have been invented and adopted within a million years.
About 150,000 years ago, change accelerated in stone working technology. "It is, as Isaac says, as if some threshhold was passed:, a critical threshold in information capacity and precision of expression," (Lewin, 1989, p. 115). Presumably, for any given human population, the crossing of this threshold was caused by a sufficient number of advantageous mutations originating in them, or more likely, reaching them from the populations where the original mutations had occurred.
The major technical development that brought the Acheulian era to an end was the development of the Levallois technique in which a carefully prepared core was first constructed, from which virtually complete flakes could be struck at a single blow, to be followed by a retouching to give the final desired shape. One of the major advantages of this new technique was a greater efficiency in the use of raw materials. An Acheulian tool maker could produce 5.1 to 20.3 centimeters of cutting edge from .45 kilograms of flint, whereas a Mousterian (as the new technology is referred to) tool maker could strike 10.2 meters of cutting edge from the same quantity of flint (Lewin 1980, p. 116). This was a clear improvement that would have been adopted earlier if the humans of the period had possessed the required intelligence. Unfortunately, the two step procedure of constructing a core and then striking it just as required to produce the desired blades required considerable intelligence. Presumably, when sufficient mutations had accumulated in a population, the newer technique was adopted. Plausibly, individuals of unusual ability might have invented the improved technique earlier, but in the absence of a high enough average ability, the technique might have died with the inventors.
Eventually, the Middle Paleolithic tools were replaced with those of the Upper Paleolithic, which were finer. In Europe, the transition went along with anatomically modern humans replacing the Neandertal, making it very plausible that the modern humans were more intelligent, although the size of the brain case did not increase. (There is some dispute as to how perfectly the replacement of the Neandertals corresponds with the change in the tool kits). Also with the shift from the Middle Paleolithic to the Upper Paleolithic were a number of other changes including the introduction of bone and ivory as raw materials, and the production of elaborate works of arts. These make it very likely that intelligence indeed increased, probably due to replacement of the Neandertals by new arrivals who benefited from more accumulated mutations.
As Mellars (1994, p. 49) recently put it, "there can be no doubt that the whole spectrum of stone tool production in Upper Palaeolithic communities shows a degree of dynamism and creativity which contrast sharply with the much more uniform and conservative patterns of technology documented throughout the long time ranges of the Lower and Middle Palaeolithic periods." He had earlier summarized the evidence (Mellars, 1991) and discussed the possibility that (Mellars, 1989, 357) "the increased complexity apparent in Upper Palaeolithic technology reflects-at least in part-some kind of fundamental change in the basic structure of human thinking or cognition associated (at least broadly) with the transition from archaic to modern human populations." The most obvious explanation of this is that the intelligence of the earlier populations had not yet reached the levels required for the Upper Palaeolithic technology.
Wynn (1985) after examining stone tools, classifies the makers of Oldowan scrappers as using only preoperational thinking in the Piagetian scheme, while the makers of Acheulean artifacts from Isimila as using operational concepts, partially because the later work exhibited a high level of symmetry. However, Wynn did not believe Levallois technique required more intelligence. He states it is a difficult technique to master, but not one that is difficult conceptually. Gowlett (1984) is another author who has emphasized the intellectual abilities of early hominids.
It is hard to imagine that during the long periods when humans used only primitive technologies, that the only thing preventing them from using more sophisticated technologies was that no one had discovered these technologies. It is implausible, for instance, that during very long periods of time (thousands of years) that someone would not have invented fancier methods of knapping stones, or the idea of hafting tools. Given the superiority of these methods, they would have been widely used had the population been intellectually capable of mastering their use.
The conclusion is that the earlier populations were of lower intelligence than current populations. With ongoing selection for intelligence it is likely that intelligence gradually increased. This evolution of intelligence presumably took the form of the occasional appearance of intelligence increasing mutations, and then the gradual diffusion of these mutations. The slow rate of increase of intelligence would be consistent with the rate at which intelligence increasing mutations were occurring limiting the increase in intelligence, rather than any cultural factors, which operate much more rapidly.
There is other evidence for gradual increases in intelligence within relatively recent periods. Whallon (1989) points out that two major demographic events occurred in the earlier part of the Upper Palaeolithic, the expansion of human populations in Australia and Siberia, arguing that the occurrence of these two events after a long period of human presence on earth requires an explanation. He argues these required new socio-cultural structures, but that these structures would have required the development at this time of even more fundamental human capacities for conceptualization and communication. He associates most of these changes with a greater capacity for more complex language, but a reading of his argument shows that all of the required adaptations could have resulted from a higher level of intelligence, with humans earlier not having the intelligence needed to settle these relatively difficult environments of low resource density and high unpredictability, and then settling them once they had developed the required intellectual abilities to support the cultural and communicative changes required.
To argue that humans very early had high levels of intelligence requires explaining why they did not settle these difficult environments. To argue they had not yet developed necessary cultural traits raises the question of why not. It is far simpler to argue that intelligence had been gradually increasing, and at earlier periods it was inadequate to provide the cultural techniques needed to settle such areas. As Whallon points out, the obstacle could not have been the development of specific cultural forms since the forms required for the Australian desert and for the cold of Siberia are quite different. However, developing the relevant cultural forms (of kinship, past and future tenses in language, the ability to communicate complex concepts, to maintain rule based social organizations required to avoid wasting fights over resources, etc.) could have required high intelligence (not his word, but his words seem to imply intelligence) which had not earlier existed.
One terminological implication of the unidirectional selection should be noted. It is frequently argued that one cannot speak of more advanced or more primitive populations because all populations that have survived to the present are well adapted to their environment, as evidenced by their having survived. However, if all populations are evolving in the same direction, it does make sense to discuss how far populations have progressed in the common direction. For what ever characteristic being discussed, it does indeed make sense to speak of some populations as advanced, and others as primitive.
At first glance, if all current populations originated from a common population, and each descendant population had experienced similar selective pressures, the descendant populations would have experienced similar shifts in gene frequencies. Thus, we would expect them to have similar intelligences.
One exception to this principle would be the action of chance, what is known in population genetics as drift. If a population is small, the accumulated action of chance can cause the frequency of a single gene in one population to differ considerably from that in another population (see any population genetics text such as Cavalli-Sforza & Bodmer, 1971). If intelligence was determined by a single gene, observed population differences in intelligence could easily be explained by drift. However, if drift was the only factor operating, different intelligence promoting alleles would predominant in different populations. One population might have an advantage in having a higher frequency of one intelligence promoting allele, and another population would have an advantage in the frequency of another intelligence promoting allele. Many of the differences in frequency would cancel each other out, leaving relatively small differences between populations in intelligence, even if there were large differences in the frequencies of specific intelligence promoting genes.
If we leave aside the influence of differential natural selection and drift, natural selection with a uniform strength would apper unable to change gene frequencies sufficiently to produce population wide intelligence differences. Yet we do observe such differences. Why? A possible answer is that, if populations do differ in size, they will differ in number of advantageous mutations. This will lead to differences in intelligence.
Incidentally, this same theory could be applied to other issues such as the evolution of disease resistance. The disease organisms in a large population should have evolved more effective mechanisms for overcoming the host's defenses than the organisms in a small population. When the populations come into contact, there will be more diseases spreading from the large population to the small population, than from the small to the large population. This is indeed what was observed when the New and Old World populations were brought into contact. The diseases introduced from Europe and Africa into the Amerindian populations were more numerous and caused more harm than the diseases introduced from the Americas into Europe (of which syphilis appears the chief example).
The fact that more diseases spread from the Old World into the New World, than in the other direction, is consistent with the Old World population having indeed been significantly larger than the New World population during the period when the two populations were separated.
Once such intelligence related genes had appeared in a population and reached a high enough frequency that mere random variation could not eliminate them (even advantageous mutations can disappear through the operation of random factors), natural selection would have caused these genes to increase in frequency and to gradually spread until they had reached all of the populations that were exchanging genes with the populations where the mutations first occurred.
What could happen to stop the spread of intelligence increasing mutations? Obviously, if there was a large barrier to human migration, such as an ocean across which people did not move, the spread of the advantageous alleles would be stopped. Thus, one would expect that certain advantageous mutations would have reached populations on one side of such a barrier, but not on the other side.
Depending on which side of the barrier a particular advantageous mutation emerged, there could be different favorable mutations on each side. For instance, it is quite plausible that certain mutations originating in the Americas were prevented from reaching Asia by the Pacific Ocean, while other mutations originating in Asia were prevented from reaching the Americas by the Pacific Ocean.
Current thinking is that the variations in intelligence between individuals are related to variations in a large number of genes. While the magnitude of the effects of variation at different genetic loci presumably vary, it is plausible that the individuals who have received the larger number of advantageous mutations have the higher intelligence. Of course, strictly speaking, the individuals with the smallest number of advantageous mutations could have had the mutations that exert the greatest effects, but it is a convenient shorthand to talk merely in terms of the number of advantageous mutations.
Likewise for populations. The population that has received the greatest number of advantageous mutations would normally have the highest average intelligence. This brings us to a natural question. Is there any reason to believe that populations on one side of a barrier will have received more mutations than on the other side? Yes, there is.
Given the same mutation rate on all continents (and there is no reason to believe it differs) the number of favorable mutations (and only a small percentage of mutations are likely to be intelligence increasing) will be proportional to a continent's total population. Admittedly, a mutation may take longer to diffuse through a large continent's population than through a small ones population, but eventually any advantageous mutations should spread throughout the whole population. Thus, we reach the conclusion that more favorable mutations should be found on the side of a barrier with the larger population.
Biraben, (1980, see the table in Cavalli-Sforza, Menozzi, & Piazza, 1994, p. 68) has estimated prehistoric populations. The total world population at 400 B. C. is estimated to be 162 million. Oceania is only 1 million and the Americas 6 million. Since the above estimates were for 400 B. C. when many Old World areas had agriculture, the population differences may be somewhat overstated. However, given the large area of Eurasia, it is plausible that its total population at all times was appreciably larger than that in Australia or the Americas.
As noted earlier, this implies that these two latter areas would have a lot fewer intelligence raising mutations during any particular period. This would in turn imply that over any particular period, such as that since the first settlers reach Australia or the Americas, that any given degree of selective pressure would have produced a greater increase in intelligence in Eurasia than in Australia or the Americas.
Let us start the discussion with the case of isolated populations with no gene flow between them. The population's expected average intelligence would vary with the number of relevant mutations that have occurred in it. In turn, the total number of favorable mutations experienced would be proportional to the population size (and to time).
The smaller, more isolated populations would lag in intelligence. Populations for which this effect would be expected to be important include Australia and the Americas. Both have relatively small populations that have been isolated from the rest of the world for most of their history.
Roberts, Jones, & Smith (1990) have reported a date of 50+ years for human related material from North Australia. Although the Australian population was probably intellectually advanced when the continent was settled (they had to be able to build at least bamboo rafts in order to cross the open ocean and settle the Australian/New Guinea continent), after settlement it was probably isolated from mutations originating elsewhere in the Old World. With a population too small to generate as many mutations as the much larger Eurasian population, it would have gradually lagged further and further behind Eurasia in intelligence, even if the selective pressures for intelligence were as strong.
Might there have been a continued arrival of new Eurasian genes? Probably not. The Australians on upon European contact lacked ocean going boats. Most likely, the continent was settled by accidental immigrants who were shipwrecked there while attempting voyages along the coast of the Sunda shelf, which is now Indonesia (for a summary history see Jones, 1989, pp. 754-756). The first settlers were unopposed and had a virgin continent to exploit. Thus they were able to settle and to flourish, even if upon arrival they were tired, unorganized, and not knowledgeable about the terrain or food.
However, once the land was settled, newer arrivals would have a much smaller chance of contributing to the Australian gene pool. Like many other hunter-gatherers, the Australians encountered by the first Europeans were suspicious of strangers and hostile to members of other groups not related to them. Their ancestors were probably similar. Thus, after the first group had settled the land, more recent arrivals would have been treated as hostile, and would be expected to have been exterminated by the first arrivals (Jones 1989 argues that more recent arrivals would probably have been killed, although he allows for the possibility of women being incorporated as wives). Upon arrival, probably as a result of a raft being blown off course, the newcomers would have been unorganized, weak, and few in number. This would have made it possible for them to be killed, if those already there had wished to do so.1 New arrivals would have had the disadvantage of not knowing the terrain, or how to exploit local food sources. Hunting and gathering by the first settlers would have lowered the density of food resources, putting new arrivals at a disadvantage.
Also, as sea levels rose, the distances from Indonesia to Australia grew. This may have prevented, or even eliminated any further settlement and gene flow.
After the initial Australian/New Guinea settlement, any favorable genes reaching the Indonesian Archipelago would have been unlikely to reach the Australians. The Australians would have gradually fallen behind in intelligence due to their isolation from the rest of the world's population.
The above argument is strongest if once Australia was settled, there were no further arrivals of peoples from Eurasia who could have brought intelligence raising alleles from Eurasia. However, some argue that the prehistoric Australian human skeletal remains differ sufficiently from each other to imply the arrival of more than one wave of migration (Brown, 1993). Variations in morphology and gene frequencies among various Australian populations have been interpreted as evidence of multiple waves of settlement (Cavalli-Sforza et al. 1994, pp. 345-346). In particular, Thorne has identified two morphological types of late Pleistocene Australian crania which he interprets as evidence of two separate migrations to Australia (Thorne 1977 as cited by Habgood, 1989, p. 259). The arrival of the dingo, a semi-domesticated dog, almost certainly a companion of people, at about 4 thousand years ago, shows that at least one other successful incursion occurred (Jones, 1989, p. 756).
Shortly before the first Europeans arrived, there were trepanging visitors to northern Australia from what is now Indonesia (Macknight, 1976), but they were too few and too late to have an appreciable genetic impact.
A somewhat similar theory is provided by Thorne and Wolpoff (1981) to explain the larger facial size and masticatory apparatus in the peripheral regions of Australasia. They hypothesize that technological progress in food preparation first occurred in South China, where genes for reduced masticatory apparatus appeared. These gradually spread to the periphery of the region in Australia. They say that (p. 348) "while some changes might eventually characterize the periphery, by this time further reductions would have occurred at the center." While their argument does not explain why the shrinkage of the masticatory apparatus should proceed more rapidly in the center than in the periphery, their theory does have some resemblance to the theory proposed here. The theory proposed here makes the progress more rapid at the center because its population is larger, and the total number of favorable mutations greater. Incidentally, if intelligence does lead to greater progress in food preparation (such as the discovery of cooking, or of the ability to make pots for boiling), the theory here could explain the larger masticatory apparatus in the Australians.
So far only a theoretical case has been made for why lower intelligence in Australian aboriginals and American Indians should be expected. It is now time to look at the evidence to see if the theory is supported.
The evidence is that Australian aborigines are low in intelligence in comparison to other populations (Seagrim & Lendon, 1980, and Klich, 1988, provide an introduction to the literature).
McElwain & Kearney (1973, p. 53) summarize the results of a number of intelligence tests. The aborigines do consistently worse, with the disadvantage greatest on those with a high verbal component. On Raven's Progressive Matrices the difference is given as .95 standard units. The Queensland Test restults are perhaps the most useful. This is a modification of a test (the PIR test) devised to select troops from the Pacific Islands. 'se of this test in Papua and New Guinea reduced the proportion of those unable to master the basic Australian Infantry training from 20% to about 2%. It thus appears to have validity in indicating the ability of a population from a different culture to master European techniques. The material is completely non-verbal in both administration and response and the material is non-representational with no pictures and no object used that has a common use or meaning. The scores are reported to be .99 standard units below that of Europeans (McElwain & Kearney, 1973, p. 53), with the scores varying with the extent of contract with Europeans. "the aboriginal groups are inferior to Europeans, and in approximately the same degree as they have lacked contract with European groups. The Dunwich children give results very close to those for European children, the Palm Island results are lower and the remote areas of the Northern Territory are further depressed" (McElwain & Kearney, 1973, p. 47).
Reference to the test manual (p. 123) shows the Palm Island group to be one where "Traditional tribal life has been absent for many years and only a few old people are familar with Aboriginal languages. The Aborginal people have been drawn from tribes from all parts of Queensland and have no common language except English and a form of camp-Pidgin. Very little of the food consumed is derived from native sources or by traditional means." Of the other medium contact group, that at Cherbourg, it was said "Tribal life and language are virtually extinct."
To give a flavor for the results, Figure 1 shows the results for a European group Taringa State Primary School, a Brisbane suburb, a medium contact aboriginal school (Palm Island), and a low contact aboriginal group (Maningrida Schoo. in Arnhem Land) whose tribal life was described as almost intact. The age patterns are rather interesting, with there apparently being a ceiling effect for the European children, and the low contact aboriginals shows surprisingly little improvement with age.
Although not graphed, the Dunwich European and aboriginal samples (given for only three age groups) are indeed very similar.
De Lacey (1971, 1972) has reported Peabody Picture Vocabulary test scores for high-contact aboriginals (urban, not speaking a native dialect) and for low-soci-economic status whites. The 40 Northern territory aboriginals averaged 64, and the 80 Wollongong low-socio-economic white children averaged 94, a difference well beyond the .01 level of probability. Interestingly, on Piagetian classificatory ability tests the aborigines were in the same range as the low-socioeconomic status whites (i.e, below the white average) (De Lacey, 1970, 1971). De Lacey (1972) also reports Peabody results for Bourke Island part aborigines (63 IQ) and Bourke Island low socio-economic status whites (87 IQ).
Of course, it is hard to know from test results whether the poor performance is due completely to environmental effects, or partially to genetics. The controversy with regard to aborigines appears in form and nature of arguments to be very similar to that in the US about blacks and whites. Space does not permit reviewing the issue here (Jensen, 1980, is the standard early source and Herrnstein & Murray, 1994, give more recent references)
One preliminary issue should be dealt with. Much of the work done with aborigines has involved Piagetian tests, especially of conservation. Those working in the Piagetian tradition (including, I suspect, the authors of the cited studies) do not think of these as intelligence tests. However, the results of these tests do correlate well with traditional intelligence when used with young children, and with performance on tests of academic achievement, including mathematics and reading (see Table 14.1 in Jensen for a long list of the correlation coefficients that have been discovered in various studies). Indeed, as Jensen (1980, pp. 669-676) points out, the individual items of these tests appear to be superior to the individual items on standard intelligence tests. The tests appear to involve less knowledge that is specific to Western cultures than some may think.
Consider the conservation of volume. Seagrim & Lendon (1980, Chap. 3) describe in detail their procedures. For instance, for the conservation of quantity the test starts with pouring water from one glass to another of the same size and confirming that the child understands they contain the same quantity. The water from one of these glasses is then poured into a tall, thin glass and the child asked if it still contains the same amount as before, with the practical implications made obvious by offering to give the child one of the glasses. Interesting, young children will normally believe there is more water in the taller glass than in a shorter glass, even though the water had just been poured from an identical glass into the taller one. As children mature they come to understand that the quantity of water is conserved when it is poured form one glass to another. The child is then considered to have acquired the concept of conservation. Questions are used to establish whether the child understands the concept of conservation of volume, and the idea of reversibility. In general, more intelligent children make the transition at an earlier age.
A similar test for conservation of weight used identical balls of plasticine. Two identical balls were shown to have the same effect on simple balance, and the child was questioned to be sure he understood the role of weight. "The child was then asked to deform one of the balls of plasticine and to make judgements about the consequences of placing it and its equal partner on the pans of the balance." The child would then be questioned to see if he really understood that weight was unchanged when he deformed the ball of plasticine.
Tests of this type can be given to children not exposed to Western cultures since they will have had experience with such simple tasks such as pouring liquids from one container to another. Indeed, it could be argued that in the dry Australian desert a knowledge of the idea of conservation would be more important than in Western civilization, where water conservation is unimportant. Certainly, the child who can be deceived about whether he was getting as big a drink as another by simply giving him less, but in a taller container would be at a disadvantage.
In the US, differences between whites and blacks have been found using Piagetian tests that are similar to those found using traditional intelligence tests. Interestingly, US aboriginals score well above blacks and close to very low socio-economic status whites, although they are culturally further (many being bilingual) from the white majority than the blacks (Gaudia, 1972). While the charge is frequently made that Westerners always do better on tests designed by Westerners, this is not true for the Piagetian tests, and Arctic Eskimos have been found to do better than white Canadian children (McArthur, 1968, p. 48) on many Piagetian tests, including one of volume conservation (such as employed with Australian aborigines), and Canadian Indians do almost as well as Eskimos (Jensen, 1980 citing Vernon,1965, and McArthur, 1968).
A sample of adopted and fostered aboriginals (typically of mixed European and aboriginal ancestry) children in Adelaide that had been reared in the homes of Australians showed performance on tests of conservation of quantity and conservation of weight that was significantly poorer than the norms for Europeans, although on other tests, including serration, the Nixon test, and the Peabody Picture Vocabulary test, the performance approximated European norms (Dasen, de Lacey, & Seagrim, 1973). The majority of the children were also reported to be below average in school work, and most were reported to experience particular difficulty with math. Since being raised in a European background controlled for differences in the environment, that aboriginal performance was below European norms is strong evidence for a genetic difference.
The general performance of aboriginal children in school is poor. Seagrim, & Lendon (1980, p.7) describing it as follows, "The realities are that the Aboriginal children of Australia are obliged to undergo a form of Westernized schooling which is rarely modified to suit their particular needs. This involves most of them in daily attendance at school for about eight years but leaves them mainly illiterate and innumerate. The imposition of this regime is seen by its purveyors to be in the best interests of the Aborigines and is not obviously resented by the children's parents who, one the contrary, ask only that it be more successful." If the phrase "mainly illiterate and innumerate" is accurate (and the writers are clearly very sympathetic to the aborigines and reluctant to impugn their abilities), it would seem hard to argue that the aborigines are of an intelligence similar to that of many other groups. For instance, in the United States, Amerindians after eight years of schooling would not be described as "mainly illiterate and innumerate", although they clearly perform below white norms. The evidence is that the aborigines do poorly in school and are disproportionately in slow learner classes (Callan, 1986, p. 42).
Additional evidence is supplied by studies of aborigines in the Northern Territory (de Lemos, 1967, 1969a). On Piagetian tests of conservation the aboriginal children did appreciably worse than Swiss children did on the same tests. There was a statistically significant tendency for the part-European children (even though typically only one eighth European) to do better on tests of conservation, even though both were in the same culture. This was significant at the 1% level for the tests on quantity and weight, and significant at the 5% level for the tests on area and length (de Lemos, 1967). The non-aboriginal genes had been left by various temporary male residents of the community several generations ago, and children of different ancestries were treated the same in the community. De Lemos (1967, 1969b) reports an experiment with conservation in which adult aboriginal subjects were offered a choice between two glasses of sugar. One long and thin glass had been filled with one cup of sugar in front of the subjects, and the other, a wider and shorter glass, had been filled with one and a half cups of sugar, again in front of the subject. "Eight out of twelve Aborginal women took the sugar from the long glass; that is the glass which had less sugar." (De Lemos, 1967, p. 7,). Incidentally, this illustrates the type of discriminations that are tested in a test of conservation (here of quantity).
De Lemos (1967) notes in reference to conservation that "According to Piaget's theory this concept is basic to all logical thinking, and this retardation would therefore indicate that intellectual development proceeds much more slowly in the Aboriginal culture, and that in general Aborigines would achieve a lower level of intellectual functioning than in normally achieved in the European-culture." She goes on to say "However the significant differences found between the part-Aboriginal and the full-Aboriginal children tested at Hermannsburg suggest that they may be racial differences in intelligence which could have contributed to this retardation. Vetta (1972) has critiqued her methodology.
However, Dasen (1972) was unable to reproduce in the same populationthe de Lemos results for better performance in the partly white aboriginals (and again found poor performance), leaving the situation unclear. An examination of the Dasen (1973) results shows that the part-aboriginal children generally did do better than the full aboriginal children (except on conservation of length tests) although the differences were not statistically significant. It is not known whether the difference between the two studies is statistically significant, or if it might better be attributed to sampling variability. Taking the two samples together, some support for a genetic difference can be deduced.
Of course, aboriginals need not do poorly on all tests. Kearins (1981, 1986) reports on experiments measuring memory for spatial location of objects. She found that aboriginals did better than whites. Since this was true of aboriginal who were at least a couple of generations removed from their original lifestyles, while these did not differ much from those who were less acculaturated, it appears likely that there is a genetic difference here. Kearins argued that this spatial ability was very useful for pathfinding in the desert. However, Drinkwater (1976) did not find such an advantage for a sample of non-desert aboriginals, although Kearins pointed out that even performing at the white level was impressive, since the aboriginals in general did not do this well.
Additional evidence of aboriginal superiority at spatial relations is supplied by Kearins (1988). She found that when day care children (4 to 4.5 years of age) were asked to indicate by pointing the direction to their home, 58% of the aboriginal children were correct while none of the university day care center children could do this and only 5% of those in an urban blue collar center, while the aboriginal children were significantly worse at knowing their addresses, ages, or at counting than were the white children. The aboriginal children were also significantly better at the kindergarten game of fishing (catching artificial fish) which required speed and manual dexterity.
A possible explanation for the aboriginal advantage in spatial memory is provided by (Klekamp et al.,1994) who report that Australian aboriginals have a larger visual cortex than Caucasians.
The brains of Australian aborigines also show a prominent lunate sulcus at a higher rate than in other races (Baker, 1974, p. 293), which Baker notes indicates that "the visual area does not extend nearly so far round the posterior end of the occipital lobe on to its lateral surface" in Europids as in Australids. This is a feature considered by some to be relatively primitive. Also the percentage of skulls with fronto-temporal pteriorn or one or both sides is much higher in Australids (and Negrids) than in Europids of Europe (Baker 1974, p. 299). It is not known what the implications, if any, of these morphological differences are for brain function. However, the tendency that some observers see for the Australian aborigines to retain many primitive features is very consistent with their isolation having prevented the genes for many traits from having reached them.
A possible biological basis for low intelligence in Australian aborigines is provided by their relatively small brain sizes, which is reported to be about 85% of that for the normal European (Baker, 1974, p. 292), with some of the smallest brains reported in normal people being found among them (Coon, 1962, p. 411). The most recent work (Klekamp et al., 1987) confirmed earlier work by finding a statistically significant difference in fresh brain weight with aboriginal brains averaging 1241 grams, versus 1421 for Caucasians. Harper & Mina (1981) reported statistically signifucant (p<.001) brain weight differences (from the same set of brains) in paired samples matched for age and height. Brain size (as measured by either head size or magnetic resonance imagining) is known to be correlated with intelligence (see the list of studies in Lynn 1991b; Miller, 1994; Rushton, 1994, 1995; Rushton & Osborne, 1995, and Rushton & Ankney, in press).
The isolation of the now extinct Tasmanians should have isolated them from late occurring mutations on the Australian mainland. Although no mental tests data is available on the Tasmanians, their culture is usually considered among the most primitive known. Apparently, they are the only people known that could not make fire, but had to get it from another band if theirs went out. Likewise, their stone tools were unhafted (Ryan, 1982).
Of course, in documenting the low intelligence of Australian aboriginals the purpose is not to encourage arbitrary discrimination against them. There is enough variability in humans that decisions should not be based only on group membership. However, elementary application of Bayes' theorem does show group membership to be relevant where the group averages differ (Miller, 1994).
A similar story would apply to the American natives. They test worse than Caucasians and Mongoloids (Lynn, 1991a, Table 5) even though they are considered to be Mongoloids, a group that generally tests well (Lynn, 1987). Space here does not permit reviewing the extensive literature on the intelligence of American natives (fortunately much of it is reviewed in McShane & Berry, 1988).
The best single source of evidence on American Indian intelligence is provided by the Coleman report. This sampled large numbers of children widely across the US and picked up non-reservation Indians who would be functioning in the main stream US society. Jensen (1980, p. 479) calculated the Indian/white differences as .67, .93, .79, and .93 standard deviation units at grade 3, 6, 9, and 12 for verbal IQ and .38, .83, .54, and .57 for vonverbal IQ. These were appreciably smaller than observed for blacks (in spite of their higher socio-economic condition and greater acculturation). The smaller deficit on the nonverbal tests is a widely reported result, which probably reflects a true difference in the pattern of abilities.
The Americas are believed to have been settled by a relatively small population passing over the Bering Land Bridge from Asia. They probably brought only some of the alleles for high intelligence with them from Asia. The subsequent sea level rise cut them off from the mutations arising in Eurasia. Since the Americas had a lower population than Eurasia (implying a smaller number of favorable mutations), they gradually came to lag behind the Eurasian populations in intelligence.
The parts of Siberia that the Amerindian ancestors came from is at the continent's periphery, far from the more densely populated areas. Thus, it is possible that advantageous alleles that had originated elsewhere in Eurasia had not yet reached the populations at the time that they crossed the land bridge, and that the alleles had not reached them when the Americas were isolated by the bridge's submersion.
What other predictions emerge from the theory that mutations favorable to intelligence have not reached certain populations? Right now, while the evidence is quite strong that there are genes that contribute to intelligence and other forms of behavior, exactly what these genes are and where they are located is unknown.
Evidence has recently been presented that several genetic markers are statistically more common in those of high intelligence than in those of low intelligence (Plomin et al., 1994; Plomin et al., 1995). Recently the first case of an allele that differs in frequency between racial groups and affects a mental ability has been reported (Berman & Noble, 1995). Given the rate of progress in molecular genetics, it is likely that several more alleles that have a positive or negative effect on intelligence will soon be located.
Recently, alcohol consumption by Orientals in North America was shown to be largely predicted by a single gene (Tu & Israel, 1995), with differing prevalence of the gene able to explain much of the racial differences in drinking. The above theory predicts similar patterns for intelligence affecting genes.
If the above theory is right, not only will these genes prove to differ in frequency between populations in different areas of the world, but some of the ones identified in European or northeast Asian populations (the populations most commonly studied, simply because they are convenient to the leading laboratories) will be found to be essentially absent (a low frequency may be the result of recent mixing with Europeans) in the original aboriginal populations in such areas as Australia and the Americas.
The above theory raises the possibility that certain alleles with a favorable effect on intelligence may have become fixed in European or Northeast Asian populations if they originated in these regions, (and possibly even if they originated elsewhere but reached these populations early enough for natural selection to fix them). Studies that are limited to just one group (such as Caucasians or Japanese) may not detect a correlation of these genes with intelligence. The above argument would suggest that mixed populations (such as those of mixed Australian Aboriginal and Caucasian descent) might very profitably be investigated. A finding that possession of a particular genetic marker correlated with intelligence would suggest that the marker either directly affected intelligence, or was close to a gene that affected intelligence.
Of course, in populations that are a mixture of two populations that differ in intelligence, any gene that differs in frequency may be merely serving as a marker for the extent of admixture (or for the extent of acculturation). It would be necessary to control for this. A good technique is to study siblings of mixed parentage to discover if a sibling who inherited the allele believed to raise intelligence also exhibited higher intelligence. An implication of the theory of this paper is that sibling studies (ideally of dizygotic twins) where one parent was aboriginal (either Australian or American) and one was European or Asian (i.e. what in animal genetics is called a F1 cross) would be a very good strategy for identifying alleles that affected intelligence. By having the offspring raised in the same family, the risk that a particular allele was merely serving as a marker for the extent of admixture or for acculturation would be reduced.
Many genetic markers, including blood group, human leukocyte antigen genes, and restriction length polymorphisms, are known to differ between populations (Cavalli-Sforza et al. 1994). It should be possible to estimate the extent of admixture independently of the genes believed to have a link with intelligence. Independent measures of acculturation would have to be sought as a control. This differs from the procedure of the major quantitative tract loci studies of intelligence so far (Plomin, et al. 1994; Plomin, et al. 1995), which limited itself only to Caucasians.
It was argued that some isolated areas such as Australia may have received few new mutations after settlement. However, if they experienced continued selection for intelligence, some of the alleles that the population arrived with may have become fixed, or nearly fixed in their populations. In this case, the standard deviation of intelligence should be smaller in such populations than in the populations that have been continually receiving new genes from other populations. This is a testable prediction.
Africans are generally found to have somewhat lower standard deviations than Caucasians (Jensen, 1980). This might be explained by a slower migration of alleles into Africa. Many intelligence relevant alleles would have reached them so long ago that they had become fixed, and many other alleles would not have reached them yet, even if they accounted for appreciable variation in other populations. In the areas that have had continual access to new mutations there will be more alleles that have not become fixed, causing a greater standard deviation of intelligence.
Incidentally, this ongoing process of new mutations coming into a population followed by selection for them may be the way to resolve the paradox of why there is so much genetic variation for intelligence (g), if g is a beneficial trait.
If intelligence is subject to unidirectional selection in which people with a higher intelligence always benefit reproductively from being able to outwit those of lower intelligence, it is likely that any given time there will be some of higher intelligence than others, thus solving the problem.
As intelligence gradually increases, it is to be expected that a few individuals with sufficient intelligence to do psychometrics and discover the concept of g will emerge. At this time, only a small fraction of the population is likely to have sufficient intelligence to do psychometrics and to understand the concept of g. Thus, the finding of a wide range in intelligence is perhaps not as surprising as it might appear at first.
Likewise, with there being several continent sized populations of different sizes, it is to be expected that the larger ones will benefit from access to a larger number of mutations, and will pull ahead in intelligence. Thus the theory predicts that the populations of continents of different size will differ in intelligence. It is to be expected that the major innovations will occur first among the more intelligent population on the most populous continents (assuming equal selection pressure for intelligence). Thus, it is not surprising that seagoing ships and the navigation skills required to cross oceans to visit other continents first emerged in Eurasia. These innovations brought more advanced populations into contact with the populations on the less populated continents. The more advanced populations had developed more advanced technology and established control of the Americas and Australia. The superior intelligence of the Eurasian populations (primarily from Europe) led to them having a higher level of education and higher incomes that the aboriginal populations of Australia or the Americas (for documentation of the role of intelligence in affecting income see Herrnstein & Murray, 1994)
The argument that isolated populations, lacking access to mutations originating on other continents, may lack certain intelligence promoting alleles, may surprise those who remember that biologists have argued that evolution is faster in small isolated populations (Mayr, 1966). Am I arguing against this generally accepted proposition? No. The two propositions are really different.
The belief that evolution occurs faster in small isolated populations can be traced to several effects. One is that deleterious recessive mutations may be eliminated more rapidly in such populations since the carriers are more likely to mate.
Another is that gene flow from outside of the population may prevent the evolution of gene combination best adapted to a particular environment, especially one on the fringes of the range of an environment. With isolation, the gene flow stops and such new combinations can emerge.
More importantly, innovations that require two or more mutations to succeed may occur more easily in small populations. Suppose that one gene could occur in forms Aa and another in Bb where AB represents a superior combination to ab, aB, and to Ab. However, ab is fitter than aB and Ab. This could happen if A and B work well together, and a and b work well together, but aB and Ab are not as successful combinations. Suppose the population starts out with all individuals being ab. If mutations occur causing A or B appear, these genes would be expected to die out since they would be appearing in the heterozygous forms of Ab or aB, which have lower reproductive success. Even if simultaneous mutations occurred which created AB, it would have only ab's to mate with, and its offspring would be Ab or aB, both of which would be at a disadvantage. Thus, a large population of ab is evolutionary stable against invasion by a or b.
Now consider a small isolated population, possibly on an island. The B allele could emerge, and by the operation of drift come to be the common allele, and possible to be even fixed. In a population that was predominantly aB, the A allele can then invade. Since AB is fitter than aB, once the A allele appears at an appreciable frequency, it can be expected to spread. Thus, the small isolated population can come to have the genotype of AB, which is fitter than ab. If the populations then become combined (perhaps by the island reuniting with the mainland), the AB variety may be able to spread at the expense of the ab. Such a spread is especially plausible if there has emerged a mechanism that keep AB from mating with those of the ab type.
The argument can easily be extended to where three mutations or more are required to produce a new variety or a new species. It is argued such combinations can most easily occur in small, isolated populations. This especially applicable to the emergence of new species where multiple mutations may be required which work well as a group, but any one of which is deleterious alone.
In contrast, this paper deals with simple mutations which increase the intelligence, and hence the fitness of the organism. These mutations are capable of invading a population and then diffusing through it. For these types of alleles, the key question is how many such mutations have reached a population.
There has been continuous worldwide selection for intelligence, although its strength may have varied with climate. Intelligence gradually increased, as reflected in the sophistication of the human tool kits. This increase was caused by intelligence increasing mutations, followed by the spread of these mutations. These mutations occurred at approximately the same rate (per million population) on different continents, but in absolute number were most common in the Eurasian land mass with its high population.
When Australia and the Americas were settled the original populations lacked certain alleles because the relevant mutations had not yet occurred, or because these mutations had not reached the relevant parts of Eurasia. After Australia and the Americas came to be isolated from the larger Eurasian populations, they did not receive further immigrants. Although a few intelligence raising mutations occurred in their populations, the smaller Australian and American populations implied that the total number of beneficial mutations was less than in Eurasia. Thus, the intelligence of the Australian and American populations came to lag behind that of the rest of the world. Of course, other factors, such as weaker selection for intelligence in certain parts of the world (such as the tropics) may have played a role.
This lower intelligence, along with other effects of isolation due to lack of disease resistance, and lack of access to cultural innovation, placed these populations at a disadvantage when they did come into contact with seafaring populations from Eurasia (Europeans) and led to European conquest of these populations. After the conquests, the lower intelligence result in the native populations having trouble competed and having an on average lower income than those of Eurasian descent in all of these countries.
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1This might not have applied to arrivals closely following the original arrivals, but such immigrants would be unlikely to be carrying alleles that the original settlers lacked.