The Evolution of Racial Differences in Intelligence
Af professor emeritus Richard Lynn
Abstract
Discusses a general theory of the processes through which the
racial differences in intelligence quotients (IQ) have evolved.
Cognitive demands for survival; Racial differences in the building
of civilization; Tropical and subtropical hominids as plant eaters;
Cold climates as a selection pressure for increased intelligence;
Mean IQs of Mongoloids, Negroids and Caucasoids in different
regions; Effect of nutrition on IQ.
***
Hominids first evolved in tropical and subtropical latitudes,
most probably reaching sapiens status in the highlands of East
Africa. From this ancestral population some groups migrated north
into Eurasia and evolved there into the Caucasoids and Mongoloids.
Colonizing temperate and cold environments, they encountered the
cognitively demanding problems of survival in cold winters. These
problems consisted principally of securing a food supply by hunting
large animals and of keeping warm in winter by making fires,
clothing and shelters. Survival in these difficult conditions acted
as a selection pressure favoring enhanced intelligence and explains
why the Caucasoids and the Mongoloids are the races which have
evolved the highest intelligence.
In a previous paper the world literature on racial differences
in intelligence was reviewed (Lynn, 1991). It was shown that the
Caucasoid peoples of North America, Britain, Continental Europe and
Australasia obtain mean IQs of around 100. Mongoloid peoples in
East Asia and in North America typically obtain mean IQs a little
higher in the range of 101-108. They are also characterized by
strong visuospatial abilities and weaker verbal abilities. The same
pattern is found in the Amerindians, but the level of their
intelligence is lower with a mean of about 90.
Negroid peoples are generally considered to have a mean IQ of
approximately 85, but this is only true of those in the United
States and Britain. African Negroids have a mean IQ in the region
of 70. American and British Negroids are more properly considered
as Negroid --Caucasoid hybrids, and hybridization has evidently
raised their intelligence levels to about midway between the two
parent races. The South East Asian races consisting of
Micronesians, Melanesians, Polynesians, Maoris and Australian
Aborigines typically have mean IQs in the range of 80-90.
These differences in intelligence test performance are
corroborated by racial differences in the building of civilization.
Only the Mongoloids and the Caucasians have built civilizations and
all the discoveries and inventions from early metal working to the
contemporary scientific advances have been made by these two races.
The consistency of the racial differences in intelligence test
performance and contributions to civilization suggests that they
have a genetic basis, as argued in detail by Jensen ( 1972, 1973,
1980). This conclusion is reinforced by the results of differences
in reaction times between the three major races of Negroids,
Caucasoids and Mongoloids. Reaction times provide a measure of the
neurological efficiency of the brain in the analysis and processing
of simple stimuli, and reaction times show the same progression of
ability from Negroids to Caucasoids to Mongoloids as has been shown
by intelligence tests. These results confirm the conclusion that
the racial differences are neurologically and genetically based. If
this is the case, the racial differences must have evolved in
accordance with the general principles of natural selection which
determine evolutionary development. The purpose of this paper is to
present a general theory of the processes through which the racial
differences in intelligence have evolved.
1. General Principles of the Evolution of Intelligence
The general principles governing the evolution of intelligence
have been established by Jerison (1973). He has shown that from
time to time populations have moved into new niches which have
entailed increased cognitive demands for survival. When this has
occurred the populations have responded by evolving larger brains
in relation to body size, i.e. Iarger "encephalisation quotients".
Larger brains have the capacity for greater intelligence and have
enabled the populations to deal with the cognitive demands of the
new niche.
There have been four major occasions in which the occupation of
new niches led to the development of larger brains and, by
inference, greater intelligence. The first was the evolution of
mammals approximately 220 million years ago. These discovered the
nocturnal niche in which they slept during the day and foraged at
night and they developed larger brains to deal with the integration
of visual, auditory and olfactory information. The second was the
evolution of the birds approximately 160 million years ago. In this
case the problems of pair bonding and co-operative feeding of the
young in nests required the development of greater intelligence and
larger brains. The third was the evolution of primates
approximately 60 million years ago. They became diurnal, occupied a
tree living niche and developed as social animals and to deal with
the problems of the new niche they again developed larger
brains.
Each of these evolutionary increases in brain size has been
accompanied by an increase in intelligence. For instance birds can
learn by the process of sensory preconditioning, i.e. they can form
an association between two neutral stimuli, whereas this cannot be
done by reptiles or fish. Only primates can master oddity problems,
where the correct choice is the odd object among three, and one
trial learning sets, where the correct choice varies from day to
day (Razran, 1971). Chimpanzees can achieve "insight", as Kohler
(1925) called it, into the use of sticks to retrieve bananas out of
reach of the hands, an ability not present in lower mammals.
The fourth major jump in brain size and intelligence led
directly to the evolution of Homo sapiens. The primates evolved as
tree living animals and by around 15 million years ago some of them
had developed into several species of apes. Around 12 million years
ago this niche started to deteriorate in sub-Saharan Africa as the
climate became drier and much of the forest was replaced by
brushwood and grasslands. The result was that some of the apes
found themselves in open grasslands and this acted as a new niche
which required greater intelligence for survival. By about 5
million years ago they evolved into the Australopithecines with
upright posture and a greater encephalisation quotient.
During the last two or more million years hominids evolved
through stages equivalent to the Australopithecines, Homo habilis,
Homo erectus and finally into Homo sapiens. During this evolution
the size of the brain increased from approximately 500 cc to 1400
cc. The selection pressures for this increase in brain size were
probably that these evolving hominids occupied a new niche as tool
makers and users and as highly co-operative social animals
(Alexander, 1989).
About one million years ago Homo erectus populations or their
equivalents were present in Africa, Europe and Asia and during the
last million years one or more of these populations evolved into
Homo sapiens. There are two theories of the final stage of hominid
evolution from Homo erectus to Homo sapiens. These are the
multi-regional and the single origin theories. The multi-regional
theory states that the Homo erectus populations in Africa and
Eurasia evolved in parallel into Homo sapiens over the course of
approximately the last half million years (Wolpoff, 1989). The
single origin theory states that the evolution from Homo erectus to
Homo sapiens probably took place in the highlands of East Africa,
and that some Homo sapiens populations then migrated into Eurasia
and replaced the Homo erectus and Neanderthal peoples (Stringer and
Andrews, 1988). According to this theory Homo sapiens populations
were established in southwest Asia, in the region of present day
Israel and Lebanon, by about 92,000 years ago and from there
further groups migrated throughout the world. By 60-40,000 years
ago they were established in northeast Asia (Jorde, 1985), and by
40-30,000 years ago they were in Europe and Australasia (Mellars
and Stringer, 1989), evolving and adapting all the time.
The dispute between the two theories is not yet resolved. In
Europe there seems little doubt that Homo erectus evolved into the
Neanderthals and that these were replaced by fully modern peoples
(Homo sapiens sapiens) around 40-35,000 years ago (Mellars, 1989)
in accordance with the single origin theory. But in east Asia there
is more evidence for continuity. Some Mongoloid morphological
features such as the Inca skull bone were present in Homo erectus
populations in China about half a million years ago (Liu, 1985) and
intermediate forms have been found in east Asia, suggesting a
gradual transition from Homo erectus to Homo sapiens (Pope, 1988).
The multi-regional theory is certainly still tenable for evolution
in the far east.
For our present purposes it is not crucial which of these two
theories is correct. The central thesis of our argument is that
either through a multi-regional or single origin process the Homo
sapiens peoples in Eurasia had to adapt to the problems of survival
in cold temperate and sub-arctic environments, while those in
Africa evolved in tropical, sub-tropical or warm temperate
environments. The thesis to be advanced is that the Caucasoid and
Mongoloid peoples who evolved in Eurasia came to occupy a new niche
which exerted selection pressure for improved intelligence to deal
with the problems of survival in the cold northern latitudes. The
thesis is an application to the problem of racial differences in
intelligence in man of Jerison's principle that the cognitive
demands of a new niche have been the selection pressure for
increases in intelligence throughout evolutionary history.
2. Tropical and Subtropical Hominids as Plant Eaters
Primates evolved rapidly following the extinction of the
dinosaurs. They lived on plant foods and those which evolved into
monkeys and apes remained largely plant eaters, supplemented to
some extent with insects. A few primates, most notably baboons and
chimpanzees, sometimes kill small mammals for food, but meat has
never become more than a small part of their diet (Strum,
1981).
The Australopithecines continued to live largely on plant foods.
This can be determined from the wear of their teeth which shows
that they subsisted largely on a diet of leaves and fruits (Grine
and Kay, 1988). Probably they also ate tubers, nuts, grass seeds
and insects (Isaac, 1978; Parker and Gibson, 1979). As the
Australopithecines were replaced by Homo erectus, and those of the
latter that lived in tropical and subtropical Africa appear to have
continued to primarily as plant eaters (Stahl, 1989). There was no
compelling reason for them to switch their diet to meat.
Temperatures in Sub-Saharan Africa vary between 20-25Centigrade
with little seasonal variation throughout the year except for the
extreme south where the climate is warm temperate. As many as 129
plant foods are available throughout the year (Peters, O'Brien and
Box, 1984) consisting of berries, fruits, bulbs and tubers during
the wet season and shoots and leaves during the dry season, and
insects such as ants and termites are also available (Stahl, 1984).
The belief that early African hominids hunted medium-sized and
large herbivores has been called into question in recent
anthropological writings by Binford (1985), who has shown that the
accumulations of bones of large herbivores at hominid sites bear
carnivore teeth marks on which stone cut marks made by hominids are
superimposed. This suggests that the large animals were hunted and
killed principally by lions and leopards and that early hominids
scavenged the bones, which they broke up to extract the marrow.
Blumenschine (1989) also argues that early African hominids were
scavengers rather than hunters. The lions and leopards were unable
to extract the brains from the cranium or marrow from large bones,
and it is these parts which are found predominantly at hominid
sites, suggesting scavenging of those parts which lions and
leopards were unable to get at.
The conclusion that people in tropical and subtropical latitudes
were never greatly reliant for their food supply on the hunting of
animals for meat is supported by observations on contemporary
hunter gatherers. Many non-cultivating populations living in
tropical and subtropical environments subsist largely on plant
foods of which numerous species are available throughout the year
(Lee, 1968; Tooby and de yore, 1987). Contemporary Pygmies and
Bushmen eat from 60 to 110 plant foods and these constitute around
70-85 per cent of their diet (Stahl, 1984). Australian Aborigines
in the western desert obtain 70-80 per cent of their food from
plants and most of the remainder from eggs and insects. They have
no well developed group hunting techniques (Gould, 1969). The Gadio
people in New Guinea obtain 96 per cent of their food from plants
and only 4 per cent from meat (Dornstreich, 1973). The ready
availability of plant foods throughout the year, together with
insects and eggs, meant that people in tropical and subtropical
Africa never had to rely on meat for their food supply and did not
come under strong selection pressure to develop the cognitive
skills required to hunt large animals.
The life style of present day !Kung bushmen in the Kalahali
desert provides a useful insight into the relative ease of securing
food supplies for hunter gatherer peoples in tropical latitudes. As
described by Lee (1968), women go gathering plant foods about one
day in three, and men go on hunting expeditions for about one week
in three. This is sufficient to provide food for the whole group,
including infants, children and the old. The rest of the time can
be spent relaxing about the camp. For these peoples the problems of
obtaining food supplies are neither time consuming nor cognitively
demanding.
3. Cold Climates as a Selection Pressure for Increased
Intelligence
The primates evolved in tropical and subtropical climates. They
have never been able to cope with temperate environments because,
being plant eaters, they can find nothing to eat during the winter
and spring when plant foods are unavailable. They find cold
temperatures a problem, and cold periods in global fluctuations of
world temperature have put them under selection pressure for
increased intelligence in order to survive. One of these occurred
about 54-52 million years ago during the mid Eocene, when the
primates showed an accelerated increase of brain size' followed by
a period of slower growth after the return of warmer conditions
(Pickford, 1988). It can be inferred that during this period the
global cooling exerted selection pressure on primates for an
increase in intelligence.
The mid-Miocene, approximately 16 million years ago, was a warm
period and two species of hominoids (Pliopithecus and Dryopithecus)
migrated into Eurasia. They survived until the cooling which took
place at the end of the Miocene, about 14 million years ago, and
then they went extinct, except in tropical south east Asia where
they evolved into the Orangutans (Pickford, 1986). These hominoids
could survive in tropical and subtropical climates but they were
evidently not sufficiently intelligent to survive in the more
demanding temperate and cold environments of Eurasia.
The only hominid species to overcome the problems of survival in
the cold temperate climates of Eurasia were Homo erectus and Homo
sapiens. The problems of over wintering would have been
considerable even during warm periods such as the present, but
during the periodic glaciations these problems would have been much
more formidable. Most of the last 80,000 years has been colder than
today. During the main Wurm glaciation of approximately 24-10,000
years ago winter temperatures in Europe and north east Asia fell by
5-15Celcius. The terrain became cold grasslands and tundra with
only a few trees in sheltered river valleys and the environment was
broadly similar to that of present day Alaska (Nilsson, 1983).
Survival in these conditions would have called for greater
intelligence than was required in the tropical and sub-tropical
climates of sub-Saharan Africa.
4. Cognitive demands in Northern latitudes
The problems of survival in the northern latitudes of Eurasia
would have resided in the cold winters and consisted principally of
obtaining food and keeping warm. Unlike the tropics and subtropics,
plant foods were seasonal and not available for many months during
the winter and spring. People therefore became wholly reliant on
hunting large herbivores such as mammoth, horse and reindeer to
secure their food supply.
It was shown by Lee (1968) that among contemporary hunter
gatherers the proportions of foods obtained by hunting and by
gathering varies according to latitude. Peoples in tropical and sub
tropical latitudes are largely gatherers, while peoples in
temperate environments rely more on hunting. Peoples in arctic and
subarctic environments rely almost exclusively on hunting, together
with fishing, and do so of necessity because plant foods are
unavailable except for berries in the summer and autumn.
The effective hunting of large herbivores would have presented
cognitive problems. Large herbivores can run fast and are virtually
impossible to catch simply by chasing after them. It is
particularly difficult to hunt them in open grasslands such as were
present in Northern Eurasia, where there is good visibility for
several thousand yards and the herbivores have ample warning of
approaching predators. Hunting in open grasslands is more difficult
than hunting in the woodlands of the tropics and sub tropics where
there is plenty of cover for hunters to hide in. The only way of
hunting animals in open grasslands was to make use of natural traps
into which the animals could be driven. One of the commonest traps
was the narrow ravine where some of the beasts would stumble and
could be speared by members of the group waiting in ambush. In
addition, the herbivores could be surrounded and driven over
cliffs, into bogs or into the loops of rivers (Geist, 1978;
Mellars, 1989).
For effective hunting of large herbivores people would have
needed to manufacture a variety of tools from stone, wood and bone
for making spearheads and for cutting. When these peoples had
killed a large herbivore they would have had to skin and butcher it
into pieces of a size that could be carried back to the base camp.
For this it was necessary to manufacture a variety of sophisticated
cutting and skinning tools.
The second principal set of problems encountered in the northern
latitudes would have centered round keeping warm. People had to
solve the problems of making fires, clothes and shelters. Fire was
used by hominids at a Homo erectus level of evolution in
sub-Saharan Africa as early as 1.4 million years ago and in China
and Europe about half a million years ago (Goudsblom, 1986), but it
must have been much easier to acquire fire in Africa than in
Eurasia. In Africa there would have been spontaneous bush fires
from which hominids could take ignited branches, carry them back to
camp and get a domestic fire started. In the colder parts of
Eurasia during the glaciations there would have been no spontaneous
bush fires. People would have had to make fires by friction or
percussion in a terrain where there was little wood. Probably dry
grass had to be stored in caves for use as tinder and the main fuel
would have been dung, animal fat and bones. The problems of
starting fires and keeping them burning would have been
considerably more difficult in Eurasia than in Africa. In addition
clothing and shelters were unnecessary in sub-Saharan Africa but
were made in Europe during the main Wurm glaciation. Needles were
manufactured from bone for sewing together animal skins and
shelters were constructed from large bones and skins (Geist, 1978;
Mellars, 1989).
The problems of hunting, butchering and skinning large
herbivores and of making clothing would have required the
construction of a greater variety and sophistication of tools than
were needed in tropical and subtropical environments. This has been
confirmed by Torrence (1983) who has demonstrated an association
between latitude and the number and complexity of tools used by
contemporary hunter gatherers. He found that peoples in tropical
and subtropical latitudes have between 10 and 20 different tools,
whereas those in the northern latitudes have between 25 and 60.
Furthermore, northern peoples made more complex tools involving the
assembly of components, such as hafting a sharp piece of bone onto
the end of a spear and fixing a stone axe head onto a timber
shaft.
The manufacture of sophisticated tools and making fires,
clothing and shelters would have been cognitively demanding. Those
groups which could not succeed would have died out, leaving those
with alleles for higher intelligence as the survivors. Through this
process the Caucasoid and Mongoloid peoples of Eurasia would have
evolved higher average intelligence levels than the Negroids
exposed to a less cognitively demanding environment in sub-Saharan
Africa.
5. Enhancement of General, Verbal and Visuospatial intelligence
in Caucasoids and Mongoloids
Survival in the cold winters of Eurasia would surely have
required an increase in all the three major components of
intelligence, namely general, verbal and visuospatial ability.
General intelligence, the general ability present in all cognitive
tasks, would have been needed to deal with all the new problems
encountered in the cold northern environments such as building
shelters and fires, making clothes and manufacturing more efficient
fools for killing, butchering and skinning large animals. Improved
verbal abilities would have been needed for better communication in
discussions of how to solve these problems, for planning future
activities and for transmitting cultural knowledge and skills to
children. Improved visuospatial abilities would have been needed
for planning and executing group hunting strategies, for accurate
aiming of spears and missiles and for the manufacture of more
sophisticated tools and weapons from stone, bone and wood. Fathers
would have shown sons how to chip flints to produce good cutting
tools, make spears with sharp points and so forth, and these skills
would have been conveyed largely by watching and imitation, much as
craft skills are learned today by apprentices watching skilled
craftsmen, rather than by verbal explanations. Hunting and tool
making would have been undertaken principally by males and this
would be why it has virtually always been found that the
visuospatial abilities are stronger in males than in females (Lynn
and Petersen, 1986).
We saw in the data set out in the previous paper that general,
verbal and visuospatial abilities are all higher in the Caucasoid
peoples as compared with Negroids. The magnitude of the Caucasoid
advantage is about the same for all three abilities, namely about
30 IQ points for the Negroid-Caucasoid comparison and about 15 IQ
points for the difference between Caucasoids and Negroid-Caucasoid
hybrids in the United States and Britain. It is true that Jensen
and his co-workers have found that the differences are slightly
less for the verbal abilities than for general intelligence and the
visuospatial, but this differential is quite subtle. The broad
pattern is for a 30 IQ point rise in all three abilities,
suggesting that all three abilities came under selection pressure
for enhancement to about the same extent.
It is apparent that the intelligence of the Mongoloids evolved
somewhat differently. The Mongoloid peoples have slightly higher
general intelligence than the Caucasoids, markedly higher
visuospatial abilities and somewhat weaker verbal abilities, and we
must now consider how this pattern of abilities could have evolved.
The reason that Mongoloids have more highly developed general
intelligence than Caucasoids can be attributed to the colder
winters they experienced and hence the stronger selection pressure
for increased intelligence. Mid-winter temperatures in north east
Asia are colder than in Europe, particularly inland in the area
around Lake Baikal where the classical Mongoloids evolved. In the
main Wurm glaciation the temperatures were some 5-15 Celcius colder
than today (Nilsson, 1983). These cold periods were particularly
severe for the Mongoloids because the Himalayas iced up and acted
as a southern barrier, so that the Mongoloids were trapped in a
cold pocket between the Himalayas on the south and the arctic
Chersky mountains on the north. It was in response to this severe
cold that the Mongoloids evolved their distinctive morphological
cold adaptations to reduce heat loss, such as the shortening of the
limbs, the flattening of the nose into the face, the thick black
hair, the reduction of the beard in males because moist exhaled air
in very low temperatures freezes on the beard and then freezes the
face; and the epicanthic fold, a thickening and extension of the
eyelid near the nose which serves to reduce reflected glare from
snow and ice (Coon, 1962; Krantz, 1980). These morphological
adaptions are most pronounced among the classical Mongoloids,
particularly the Buriats and the Tungus who lived in the coldest
region of inland eastern Eurasia. They are less pronounced among
the southern Chinese and among the Ainu, the original inhabitants
of Japan for whom the climate was more maritime and therefore less
severe.
If the selection pressures for enhanced intelligence acted on
the Mongoloids uniformly for general intelligence, verbal and
visuospatial abilities, as it apparently did for the Caucasoids,
then all three abilities should be elevated in the Mongoloids above
those of Caucasoids. Yet the evidence shows that this is not the
case and that the Mongoloids have evolved a different pattern of
abilities consisting of strong visuospatial and weak verbal
ability. The most probable explanation for the evolution of this
pattern is that one or more mutations for it occurred in the
Mongoloids which did not occur in the Caucasoids.
A possible hypothesis is that mutations occurred in Mongoloids
which shifted the balance of the verbal and visuospatial abilities
in favor of the visuospatial. The hypothesis posits that there is a
negative association between the verbal and visuospatial abilities
which arises because tile more cerebral cortex is devoted to one
the less is available for the other. This implies that it should be
possible to demonstrate that the verbal and visuospatial abilities
are negatively correlated. It has been shown that, when general
intelligence is controlled for, this is the case (Lynn, 1987).
Vernon (1990) has produced further evidence in favor of the
hypothesis although he considers that the negative correlations
arise from a statistical artefact. In my own opinion this is
incorrect and the negative relationship is a genuine one (Lynn,
1990a).
If this hypothesis is correct, the mutants for the enhancement
of the visuospatial abilities at the expense of the verbal would
have spread in the Mongoloids because they conferred a survival
advantage. This in turn must mean that although increased verbal
and visuospatial abilities were both advantageous for survival in
the cold environments of Eurasia, the visuospatial abilities must
have been that bit more important. It is not difficult to
understand why this would have been so. It would have been because
of the crucial role of strong visuospatial abilities for making
sophisticated tools and weapons and for the planning and execution
of group hunting strategies. Good verbal abilities were not quite
so important and were worth sacrificing for a gain in the crucial
visuospatial abilities.
6. Evolution of Intelligence in South East Asians and
Indians
The south east Asian races evolved either from Homo erectus
populations which were present in this region about 1 million years
ago (Jones, 1989) or alternatively, according to the single origin
theory, by migration of Homo sapiens populations across India, into
south east Asia, through the Indonesian archipelago and thence into
Australia and the Pacific Islands. Whichever of these two theories
is correct, these peoples would have spent some time in temperate
Asian environments before they migrated eastward. This would have
exerted some selection pressure for enhanced intelligence, but the
duration of their exposure to cold winters would have been
relatively short as compared with the experience of the Caucasoids
and Mongoloids. By the time the main Wurm glaciation came on, about
24,000 years ago, these peoples were settled in the tropical
Pacific Islands and in Australia. Hence their intelligence levels
were raised a little above those of the Negroids but not to the
high level of the Caucasoids and Mongoloids.
The Indian Caucasoids had a longer period of exposure to the
cold winters of northern India, which were significantly colder
during the main Wurm glaciation than they are today. This explains
why Indians invariably obtain higher intelligence levels than
Negroids, whether they are in India or South Africa,,where their
mean IQs are around 85 or in Britain where their mean IQs are
around 95, as shown in our review.
7. The Amerindians
It is well known that the Amerindians originated from peoples
who crossed the Bering Straits and made their way southward into
the Americas. Amerindians artifacts have been dated at 30,000 years
ago in California (Bade, Schroeder and Carter, 1974), at 32,000
years ago in north east Brazil (Guidon and Delibrias, 1986) and at
33,000 years ago at Monte Verde in Chile (Dillehay and Collins,
1988). It must have taken several thousand years for these peoples
to have found their way from Alaska to south America. The Bering
land bridge was open a number of times during successive
glaciations between approximately 80 - 25,000 years ago, and some
consider it possible that the first American peoples made the
crossing on foot sometime during this period, perhaps as early as
42 - 36,000 years ago, allowing 3,000 years or so for some of them
to make their way down to south America.
If this chronology is correct, there must have been an archaic
Mongoloid people in north east Asia around 60 - 50,000 years ago.
Some of these must have migrated north east into Kamchatka and the
Chersky Peninsula to make the crossing of the Bering straits by
around 42 - 36,000 years ago. Other archaic Mongoloid peoples
remained in north east Asia. The common origin of these two races
is known from a number of genetic similarities such as blood
groups. For instance, the Rhesus negative allele is rare and the
Diego blood group unique to these two races and they both have
similar coarse and straight black hair, shovel incisor teeth and
the Inca bone (Krantz, 1980).
The studies reviewed previously showed that the profile of
intelligence of the Amerindians is similar to that of the
Mongoloids in so far as they have strong visuospatial and weak
verbal abilities. The whole profile is lower than that of
Mongoloids by around 1 standard deviation, so that their general
intelligence stands at around 90 as compared with a Mongoloid mean
of around 105. It appears as if some factor set the cognitive
profile of strong visuospatial -- weak verbal abilities in archaic
Mongoloids, and that some subsequent selection pressure raised the
whole profile in the Mongoloids, leaving that of the Amerindians at
a lower level. The most probable explanation is that the
distinctive profile became established among archaic Mongoloids
during the first Wurm glaciation sometime in the period 60 - 40,000
years ago, or possibly in earlier glaciations over the course of
half a million years if the multi-origin theory is correct. The
reason that this cognitive profile became established was the
paramount selective advantage of strong visuospatial abilities for
survival in a severe periglacial environment.
The main Wurm glaciation of approximately 24 - 10,000 years ago
must have been the factor raising the cognitive abilities of the
Mongoloids and leaving that of the Amerindians at a lower level.
The Amerindians escaped exposure to the severe cold of the main
Wurm glaciation. Once they had crossed the Bering Straits and made
their way down into the Americas they would have found life a good
deal easier than their ancestors had been accustomed to in north
east Asia. They would have found a number of herbivorous mammals
such as mammoth, horse antelope, sloth, armadillo and bison who
were quite unused to being hunted by man. Normally predators and
prey evolve together in that over the generations predators become
more skilled at catching prey and prey become more skilled at
evading predators. Through this process an equilibrium is
maintained and both predators and prey are fully taxed to survive.
But the herbivorous animals of the Americas had no experience of
predation by man and would have been easy game for the skilled
hunters who had evolved for many thousands of years in the more
difficult environment of north east Asia. So they would have found
large numbers of inexperienced herbivores who were easy to catch
and, in addition, as they moved southward they would have found
that plant foods were more readily available. They ceased to rely
exclusively on hunting for their food and adopted the easier life
style of the hunter gatherer in which plant foods played a
significant part in their diets (MacNeish, 1976; Hayden, 1981).
Thus in the new environment of the Americas survival would have
been much easier. The Amerindians would have retained their
elevated level of general intelligence, as compared with the
Negroids, which their ancestors would have gained in north east
Asia during the early Wurm glaciations. They would also have
retained their well developed visuospatial abilities. These enabled
them to continue as effective hunters and there would have been no
selection pressure to evolve any different pattern of abilities.
However, the selection pressure for any further increase in these
and other cognitive abilities would have been considerably relaxed.
The cognitive abilities of the Amerindians have probably increased
since they reached the Americas because intelligence has been a
fitness characteristic for all human populations. But the rate of
increase will have been relatively slow because of the relaxation
of the selection pressures for enhanced intelligence acting on
them. The history and the intelligence of the Amerindians suggests
that the main Wurm glaciation must have been the principal factor
which raised the intelligence of the Caucasoid and Mongoloid
peoples to its present level.
This conclusion enables us to answer a conundrum which has long
perplexed anthropologists. The problem is this: the first Homo?
sapiens are currently thought by many theorists to have appeared in
Africa around a quarter of a million years ago and to have been
established in the Near East by 92,000 years ago. The species lived
in small hunter gatherer bands until about 10,000 years ago, when
some groups in the Middle East and Anatolia made the Neolithic
transition to horticulture and eventually agriculture. This
involved a transition to larger settled communities which planted
food crops and kept domestic animals. This change of life style
permitted larger concentrations of populations in towns and city
states and allowed people to develop specialized skills. In
particular, it became possible to support a small intelligentsia
which was able to produce the early intellectual and technological
advances such as the construction of a written language, a system
of arithmetic, the understanding of the regularities of the
movements of the planets and so on.
This Neolithic revolution occurred in the Near East about 10,000
years ago, in northern China about 7,000 years ago and in Central
America about 5,000 years ago. The problem which has puzzled
anthropologists is why these advances should have occurred,
presumably independently, in these three locations at about the
same time. Why did they not occur two hundred thousand years ago in
Africa, or sometime in the period 90,000-10,000 years ago in
Eurasia? There were warm interglacial interludes during this period
when people could in principle have made the transition to
agricultural societies. But they didn't.
Different anthropologists have offered a variety of theories to
explain this problem. The principal theories are population growth,
increasing social complexity and climatic change. But none of these
provides a satisfactory explanation for why the agricultural
revolution did not occur at some earlier period during the last
200,000 years but had to await the end of the last Ice Age.
The answer proposed to this problem is that people were not
sufficiently intelligent to pioneer these developments until they
had been through the major selection pressure of the last Wurm
glaciation. This also explains why these advances were never made
by the Negroids or the south east Asian races who escaped the
rigors of the last glaciation. The Amerindians were in an
intermediate position, exposed to some selection pressure for
enhanced intelligence from cold, but not subjected to the full
severity of the subarctic winters to which the Caucasoid and
Mongoloid peoples were exposed.
8. Racial Differences in Brain Size
Throughout the course the evolution new species have from time
to time evolved with larger brains or, more strictly, higher
encephalisation quotients, to accommodate greater intelligence.
These increases in brain size have occurred to deal with the
problems of survival in new cognitively demanding riches. It has
been argued that one of these occasions took place when hominids
migrated from tropical and subtropical Africa into the temperate
and cold environments of Eurasia. These migrants; who evolved into
the Caucasoid and Mongoloid peoples, have invariably been found to
have higher average intelligence levels than populations descended
from those who remained in tropical and subtropical latitudes. The
question to which we turn now is whether the Caucasoids and
Mongoloids evolved larger brains to accommodate their greater
intelligence, as had happened on previous occasions in the history
of evolution.
In the last century and the early decades of the present century
there were a number of claims that Caucasoids had larger average
brain sizes than Negroids but in recent years it has come to be
widely claimed that these studies have been discredited (Gould,
1981). Nevertheless, the figures given by Gould for brain size for
the major races indicate that Mongoloid and Caucasoid brain sizes
are larger than those of Amerindians, and these in turn are larger
than those of Negroids. Gould's calculations are shown in Table 1.
Data on racial differences in brain size have also been collated by
Rushton (1989) whose results are given in Table 1.
Finally, Beals, Smith and Dodd (1984) collected results from
approximately 20,000 crania and classified them into geographical
and climatic zones. They found the largest brain size in
Mongoloids, followed in descending order by Caucasoids,
Amerindians, south east Asians and Negroids. These results are also
given in Table 1. Gould's cranial capacity estimates are given in
cubic inches, while those of Beals et al and Rushton are given in
cubic centimeters. The reason for Rushton's estimates being higher
than those of Beals et al is that the latter made a 6 per cent
reduction because the cranial capacities were estimated by filling
the crania with shot, whereas Rushton has not made the adjustment.
If this is allowed for, the two sets of readings are closely
similar and are similar also to those given by Gould.
A further large scale study which confirms that Caucasoids have
larger average brain size than Negroids has been carried out by
Broman, Nichols, Shaughnessy and Kennedy (1987). They have examined
and followed up approximately 17,000 Caucasoid and 19,000 Negroid
children from conception to the age of 7 years in the United
States. At the age 7 there was the usual gap of approximately 15 IQ
points between the two groups. The head circumferences of the two
groups have been calculated from the published data and are 50.9
(sd 1.6) for Negroids and 51.7 (sd 1.6) for Caucasoids. This
difference is statistically highly significant and provides an
approximate measure of differences in brain size, since head
circumference and brain size are correlated at about 0.8 (Brandt,
1978).
The Negroid children were slightly taller than the Caucasoid,
suggesting that possible differences in nutrition are not likely to
be responsible for the differences in head size. The magnitude of
the difference, amounting to approximately half a standard
deviation, is rather less than the difference of approaching two
standard deviations in the Beals et al data. This may be partly
because American Negroids are hybrids and partly because Negroids
mature more quickly than Caucasoids (Rushton, 1988, 1989).
Examining the data set out in Table 1 as a whole, it is evident
that the disparity in brain size between Mongoloids and Caucasoids
is about half the disparity between Caucasoids and Negroids (40 cc
as compared with 74 cc in the Rushton's data and 53 cc as against
14 cc in the Beals et al data). This broadly parallels the
intelligence test results where the Mongoloid -- Caucasoid
disparity is typically around one quarter to one half a standard
deviation, whereas the Caucasoid -- Negroid disparity is
approximately two standard deviations.
Considered in terms of standard deviation units, the Negroid
Caucasoid disparities in brain size and in mean IQs are
approximately the same, i.e. about 2 sds. The Mongoloid-Caucasoid
disparity is slightly greater in brain size than in mean IQs.
The data on racial differences in brain size show a striking
similarity to the differences in intelligence. The races fall into
the same rank order with Mongoloids highest on both brain size and
intelligence, followed in descending order by Caucasoids,
Amerindians, south east Asians and Negroids.
9. Brain Size and Intelligence in Man
Although brain size relative to body size correlates with
intelligence across species, there has been a marked reluctance
among anthropologists to admit that brain size is related to
intelligence in man.
For instance, Beals, Smith and Dodd (1984) in their paper citing
racial differences in brain size in man write of the association
between brain size and intelligence that "no convincing case for
such associations has ever been presented". Similarly "there is
even more evidence accumulating against a direct relationship
between cranial capacity and intellectual capacity" (Henneberg,
1984); and "there is really no evidence to show that brain size is
positively correlated with intelligence" (Latham, 1974).
In spite of these assertions, there is in fact quite solid
evidence for a positive association between brain size and
intelligence in Homo sapiens. A search of the literature has turned
up 16 studies on the question. In most of these, head circumference
has been taken as an approximate measure of brain size. The results
are tabulated in Table 2. It will be seen that the studies obtained
a positive correlation between head size and intelligence and in
all cases the correlations are statistically significant. The
correlations are certainly quite low, but this could be partly
because head circumference is not a perfect measure of brain size
and intelligence tests are not perfect measures of intelligence. It
is possible to correct the correlations for these unreliabilities.
The effect of this, assuming that head circumference correlates 0.8
with brain size (Brandt, 1978) and that intelligence tests have a
reliability of 0.9, is to increase the correlations by around 20
per cent. However, perhaps the most interesting study is that by
Willerman, Shultz, Rutledge and Bigler (1989) in which brain volume
was measured by magnetic resonance scanning in 40 university
students and a correlation of 0.35 obtained between brain volume
and intelligence. This result, together with the consistent trend
in the studies summarized in Table 2, puts it beyond dispute that
brain size and intelligence are positively correlated in man.
10. Conclusion
The argument is now complete. Brain size is positively
correlated with intelligence in man, and the races show consistent
differences in both brain size and intelligence. These differences
appear to have arisen because the Caucasoids and the Mongoloids
colonized a new and cognitively demanding niche when they migrated
into the temperate and cold environments of Europe and Asia. In
these harsh environments the less intelligent failed to survive,
and this left the Caucasoids and the Mongoloids as the two most
intelligent races and the only two races that have made any
significant contribution to the development of civilization. The
evolution of racial differences in intelligence in man has followed
the same principle that has operated throughout evolutionary
history, namely adaptation to a new and cognitively demanding
niche.
REFERENCES
Alexander, R.D. 1989; Evolution of the human psyche. In
P. Mellors and C. Stringer (eds) The Human Revolution.
Edinburgh: University of Edinburgh Press.
Bada, J.L., Schroeder, R.A., and Cater, G.F. 1974; New
evidence for the antiquity of man in North America deduced from
aspartic and recemization. Science, 184, 791-793.
Beals, K.L., Smith, C.L., and Dodd, S.M. 1984; Brain size,
cranial morphology, climate and time machines. Current
Anthropology. 25, 301-330.
Binford, L.R. 1985; Human ancestors: changing views of their
behavior. Journal of Anthropological Archaeology, 4,
292-327.
Blumenschine, R.J. 1989; Man the scavenger.
Archaeology. July, 26-32.
Bogaert, A.F. and Rushton, J.P. 1989; Sexuality delinquency
and r/k reproductive strategies: data from a Canadian sample.
Personality and individual Differences 10, 1071-1077.
Brandt, T 1978; Growth Dynamics of Low Birth weight infants
with emphasis on the perinatal period. In: Human
Growth vol. 2 ed. F. Falkner and J.M. Tanner, pp 557-617. New
York: Plenum Press.
Broman, S.H., Nichols, P.L. and Kennedy W.A. 1975; Preschool
IQ, New York: J. Wiley.
Broman, S, Nichols, P.L. Shaughnessy, P. and Kennedy W. 1987;
Retardation in Young Children. Hillsdale, New Jersey:
Lawrence Erlbaum.
Coon, C. S. 1962; The Origin of Races. New York,
Knopf.
Dillehay, T.D. and Collins, M.B., 1988; Early cultural
evidence from Monte Verde in Chile. Nature. 332,
150-152.
Dornstreich, M.D. 1973; Food habits of early man balance
between hunting and gathering. Science. 179,306.
Geist V. 1978 Life Strategies. Human Evolution and Environmental
Design. New York: Springer-Verlag.
Goudsblom, J. 1986; The human monopoly on the use of fire:
its origins and conditions. Human Evolution. 6,
517-523.
Gould, R. A,. 1969; Subsistence behaviour among the Western
desert Aborigines of Australia, Oceania, 39,
253-27-4.
Gould, S. J. 1981; The Mismeasure of Man, New York,
Norton.
Grine, F.E. and Kay, R.F. 1988; Early hominid diets from
quantative image analysis of dental microwear.
Nature. 333, 765-768.
Guidon, N. and Delibrias, G. 1986; Carbon-14 dates point to
man in the Americas 32,000 years ago. Nature. 321,
769.
Hayden, B. 1981; Subsistence of Modern Hunter-Gathers.
In R.O.S. Harding and G. Telela (eds) Omnivorous Primates.
New York: Columbia Univ. Press.
Henneberg, M. 1984; Comment on Beals Dodd and Smith.
Current Anthropology. 25, 321-322.
Henneberg, M. Budnik, A., Pazacka, M. and Puch, A.E. 1985;
Head size, body size and intelligence: introspecific
correlations in Homo sapiens. Homo, 36, 207-218.
Isaac, G. 1978; The food-sharing behavior of protohuman
hominids. Scientific American. 238, 90-109.
Jerison, H. 1973; Evolution of the brain and
intelligence. New York, Academic Press.
Jones, R. 1989; East of Wallace's line: issues and problems
in the colonisation of the Australian continent. In P. Mellars
and C. Stringer (eds) The Human Revolution. Edinburgh,
Edinburgh University Press.
Jorde, L. B. 1985; Human genetic distance studies.
Annual Review of Anthropology. 14, 343-373.
Krantz, G.S. 1980; Climatic Races and Descent Groups.
North Quincy, Mass: Christopher.
Lathan, M.C. 1974; Protein-calorie malnutrition in children
and its relation to psychological development and behavior.
Physiological Reviews. 54, 541-565.
Lee, R.B. 1968; What hunters do for a living. In Man the
Hunter. In R.B. Lee and I. Devore (eds), Chicago, Aldine
Press.
Lewin R. 1984; Man the scavenger. Science,
224, 861-2.
Linn, M.C. and Petersen, A.C. 1986; A meta analysis of
gender differences in spatial ability: implications for mathematics
and science achievement. In J.S. Hyde and M.C. Linn (eds)
The Psychology of Gender. Baltimore: Johns Hopkins
University Press.
Liu, Ze Chun 1985; Sequence of sediments at locality 1 in
Zhoukoudian and correlation with loess stratigraphy in Northern
China. Quaternary Research 23. 139-153.
Lynn, R. 1987; The intelligence of the Mongoloids: a
psychometric, evolutionary and neurological theory.
Personality and Individual Differences. 8, 813-844.
Lynn, R. 1990a; Negative correlations between verbal and
visuospatial abilities: statistical artifact or empirical
relationship? Personality and Individual Differences,
11, 755-756.
Lynn, R. 1990b; The role of nutrition in secular increases
in intelligence. Personality and Individual Differences. 11,
273-285.
Lynn, R. 1991; Race differences in intelligence: a global
perspective. Mankind Quarterly.
MacNeish, R.S. 1976; Early man in the New World. American
Scientist, 64, 316-327.
Mellars, P. 1989; Technological changes in the middle-upper
palaeolithic transition: economic, social and cultural
perspectives. In P. Mellars and C. Stringer (eds) The
Human Evolution. Edinburgh, Edinburgh University Press.
Mellars, P. and Stringer, C. 1989; The Human
Revolution. Edinburgh, Edinburgh University Press.
Murdock, J. and Sullivan, L.R. 1923; A contribution to the
study of mental and physical measurements in normal school
children. American Physical Education Review, 28, 209-330.
Nilsson, T 1983; The Pleistocene, London, D.
Reidel.
Parker, S.T. and Gibson, K.R. 1979; A developmental model of
the evolution of language and intelligence in early hominids. The
Behavioral Brain Sciences, 2, 367-408.
Passingham, R,E. 1979; Brain size and intelligence in man.
Brain, Behavior and Evolution. 16, 253-270.
Pearl,R. 1906; On the correlation between intelligence and
the size of the head. Journal of Comparative Neurology and
Psychology. 16, 189-199
Pearson, K. 1906; On the relationship of intelligence to
size and shape of head, and to other physical and mental
characters. Biometrika, 5, 105-146.
Peters, C.R., O'Brien, E.M. and Box, E.O. 1984; Plant types
and seasonality of wildplant foods, Tanzania to south western
Africa. Journal of Human Evolution, 13, 397-414.
Pickford, M. 1986; Major events in primate paleontology:
possible support for climatic forcing models of evolution.
Antropologia Contemporarea, 9, 89-94.
Pickford, M 1988; The evolution of intelligence: a
palaeontological perspective. In HJ. Jerison and I Jerison
(eds) Intelligence and Evolutionary Biology Berlin,
Springer-Verlag.
Pope, G. G. 1988; Recent advances in far eastern
paleoanthropology. Annual Review of Anthropology. 17,
43-77
Reed, R.W. and Mulligan, J.H. 1923; Relation of cranial
capacity to intelligence. Journal of the Royal Anthropological
Institute, 53, 322-331.
Rushton, J. P. 1988; Race differences in behaviour: a review
and evolutionary analysis. Personality and Individual
Differences. 9, 1009-1024.
* 1989; The evolution of racial differences: a response to
M. Lynn. Journal of Research in Personality, 23, 7-20.
* 1990; Race, brain size and intelligence: a rejoinder to
Cain and Vanderwolf. Personality and Individual Differences,
11, 785-794.
Schreider, E. 1968; Quelques correlations somatiques des
tests mentaux. Homo. 19, 38-43.
Sommerville, R.C. 1924; Physical, motor and sensory traits.
Archives of Psychology. 12, 1-108.
Stahl, A.B. 1984; Hominid dietary selection before fire.
Current Anthropology. 25, 151-168.
Stringer, C.B. and Andrews, P. 1988; Genetic and fossil
evidence for the origin of modern humans. Science, 239,
1263-1268.
Strum, S.C. 1981; Processes and products of change: baboon
predatory behavior at Gilgil, Kenya. In R. Harding and G.
Telela (eds) Omnivorous Primates. New York, Columbia
University Press.
Susanne, C. and Sporoq, J. 1973; Etude d e correlations
existent entre des tests psychotecniques et des mensurations
cephaliques. Bulletin Societe Royal Belge Anthropolgie et
Prehistorie. 84, 59-63.
Tooby, J. and Devore, I. 1987; The reconstruction of hominid
behavioral evolution through strategic modelling. In W.G.
Kinzey (ed) The Evolution of Human Behavior: Primate
Models. Albany (NY), State University of New York Press.
Torrence, R. 1983; Time budgeting and hunter-gatherer
technology. In G. Bailey (ed) Hunter-Gatherer Economy in
Prehistory:? A European Perspective. Cambridge, Cambridge
University Press.
Vernon, P.A. 1990; The effect of holding g constant on the
correlation between verbal and non verbal abilities: a count on
Lynn's "The intelligence of the Mongoloids..." Personality and
Individual Differences, 11, 751-754.
Weinberg, W.A., Dietz, S.G., Penick, E.C. and McAlister, W.H.
1974; Intelligence, reading achievement, physical size and
social class. Journal of Pediatrics. 85, 482-489.
Willerman, L., Shultz, R. Rutledge, J. N. & Bigler, E. 1989;
Magnetic resonance imaged brain structure and
intelligence. Paper presented at the Annual Association, June
8-11, 1989.
Wolpoff, M. H. 1989; Multiregional evolution: the fossil
alternative to Eden. In C. B. Stringer and P. Mellars (eds)
The Origins and Dispersals of Modern Humans. Cambridge:
Cambridge University Press.
About the author
Richard Lynn
is professor emeritus at the University of Ulster, Coleraine,
Northern Ireland.
Source
The Mankind Quarterly, Fall/Winter 91,
Vol. 32 Issue 1/2, p99, 23p.