-Caveat Lector-
ACADEMIC FREEDOM ENDED IN U.K.
-- How 'publisher' Wiley and Scotland's top 'university' threw to the
wolves
the psychologist who wrote about IQ and race. --
'The g Factor', a product of Brand's thirty years in the psychology of
intelligence and personality, was published in the UK by Wiley (Chichester)
in February 1996 and met with expert approval. While commending the book,
Britain's leading psychologist, Hans Eysenck, particularly remarked (in
Personality & Individual Differences 26, 1996):
"Apart from being accurate, Brand is also courageous; he deals with
'sensitive' problems in a straightforward, accurate fashion, without
treading unnecessarily on vulnerable toes."
However, the politically correct exponents of 1990's multiculturalism
thought otherwise. They urged Wiley to withdraw the book from
publication --
the modern form of censorship (applied similarly in 1997 to ex-Governor of
Hong Kong, Chris Patten, when his then publisher, HarperCollins, discovered
that his book criticized Red China).
Interviewed by the press in April 1996, Brand agreed there would tend
to be racial differences in children's speeds of school progress. Brand
cheerfully accepted he would be what critics of IQ standardly called a
'scientific racist' -- though Brand preferred the term 'race realist.' (For
use of the term 'scientific racist' see, for example, Steven Fraser et al.,
1995, The Bell Curve Wars, New York : Basic. The term had become used by
such extremist critics of IQ as Stephen Jay Gould, Leon Kamin, Richard
Lewontin and Steven Rose to describe academic psychologists like Hans
Eysenck, Art Jensen, Richard Lynn and Phil Rushton who did race research
and
came to hereditarian conclusions.) Brand believed 'The g Factor' would
vindicate his position and expose critics as hysterical 'ignoracists' whose
ideology had rendered them incapable of examining evidence; but Brand was
due for a long wait.
De-published by Wiley (on orders from their New York head office),
slated by his University Principal, and replying in kind, Brand found
himself under attack from all quarters. 'Feminists' took a special interest
as it emerged that Brand sympathized with Freud and believed in
biologically-based sex differences as well as race differences. Through
1996/7, Brand was witch-hunted, censored by his University, thrown to the
tabloid press for writing his censorship-lambasting NewsLetter in defence
of
his book, sent before a three-month disciplinary Tribunal by his University
and fired. Precisely why he was fired still remains a mystery.
The facts are as follows.
1. Brand had refused to grovel when Edinburgh University's Principal
Stewart
Sutherland told the press in April, 1996, that his apparent views on IQ
Were "false and personally obnoxious." The Principal's comments were given
wide
publicity (e.g. in the London broadsheet press). After the Principal
refused to withdraw his unprecedented condemnation, and refused to read
Brand's
book, Brand began criticizing the University on the Internet in 'The 'g'
Factor NewsLetter.' (This newsletter was issued almost daily and gave news
of, and support to victims of political correctness. It castigated
social-environmentalist ideas that people are easily conditioned, shaped or
driven into psychopathology by their experiences with people.)
2. On October 16 1996, Brand e-mailed colleagues and supporters one page of
comment which ridiculed the prosecution of a 73-year-old Nobel Laureate,
Carleton Gajdusek, who faced a 30-year jail term for non-violent
paedophilia
in Maryland c. 1985. (Gajdusek's work on 'laughing brain rot' [kuru] in
Papua New Guinea had helped the West crack bovine spongiform encephalopathy
[BSE, or Mad Cow Disease]. Gajdusek had adopted (peadophile)some forty
children from
Papua New Guinea and educated them in the United States at his own expense.
Suspension from teaching and nine months of investigation by
An E.U. Tribunal culminated, on 8 August 1997, in Brand being dismissed,
after
27 years of service, for his "gross misconduct."
Just what Edinburgh University found "disgraceful" in Brand's conduct
remains to be clarified. From the University's prosecution case to its own
Tribunal, the main alleged problem was that Brand had upset his Psychology
colleagues by his realistic and humorous observations on a range of
psychological topics, and especially on 'feminist issues' like whether
women find their greatest satisfaction in maternity. Brand's colleagues in
psychology also did not like him achieving publicity for his views. Thus
for him to have articulated the long-standing (though little publicised)
expert
consensus that some forms of paedophilia are empirically harmless (when
involving intelligent and uncoerced adolescents) was, for his colleagues,
'the last straw.' Yet what exactly was "disgraceful" in Brand's pointing to
the empirical evidence about paedophilia -- or to the empirical evidence
about race -- and indicating his conclusion that mercy should be shown to
the accused Nobelist who had pioneered the way to public understanding of
BSE? The University's final position, after nine months of work on the
subject, was that it objected not so much to what Brand had said as to the
way he had said it. -- But the same complaint could be made retrospectively
against *any* statement by an academic that finally fell foul of the
tabloid
newspapers. Essentially, Edinburgh University is requiring that no academic
should make any controversial views intelligible to the public that pays
academics' salaries.
On 24 March 1998, Brand's Appeal against his dismissal was rejected
By a Scottish High Court judge who had been selected by the University. Mr
T.
Gordon Coutts, QC, ruled that, under the UK's 1988 Education Act, British
academics -- whatever the disciplinary codes of their own universities
might actually say -- do not need to be guilty of anything as serious as
"gross
misconduct" for their universities to be entitled to sack them without
warning. Since 1988, academics can be dismissed for "good cause" -- a term
deriving from general UK employment protection legislation, but certainly
permitting dismissal for expressing views that are merely embarrassing to
an employer.* Brand's battle with Edinburgh University has thus revealed, so
far, that 'academic freedom', as usually understood,** was ended in Britain
in 1988. R.I.P.
Yet the Coutts verdict is far from being the end of the matter. For
example, it remains unclear how Brand's conduct was "disgraceful" -- even
without the requirement that the degree of disgrace should amount to "gross
misconduct." Brand's defence of his book certainly lacked modern piety,
political correctness and any undue deference to Edinburgh University's
Principal. Yet what action of Brand's was truly "disgraceful" or
"scandalous" or "immoral"? (Such are the legal ways of sacking ordinary
British workers -- operatives at biscuit factories etc.*** -- without
warning)
In contrast, it is perfectly clear how to punish today a British
academic who says genes are substantially involved in causing the empirical
link between race and IQ: he is de-published, hounded by self-styled
'anti-racists', condemned by his university, thrown to the tabloid press so
they can rake through his sex life, and fired for the slightest hint of
departure from media morality in any of his opinions. Brand had not even
called for change in the law when denying that the typical intelligent
paedophile did demonstrable harm. He had offended ideologues and hysterics
merely by pointing out that scientists know much that contradicts the press
and popular opinion -- whether about race or paedophilia. Above all, Brand
had challenged the politically correct formulation that all human
inequalities are the result of the downtrodden having suffered
'disadvantages' which utopians should be employed by the state to rectify.
Brand had disputed the environmentalistic view that society is full of
'victims' of capitalism, imperialism, racism or male chauvinism -- a view
that would express itself in the Dianamania of 1997 and in many claims for
'recovered memories' of childhood abuse. Though modern research unfailingly
shows the environments imposed upon people to account for rather little --
and their own choices of environment to count for much -- Brand's challenge
could not be tolerated by those who enjoy their roles as the paid champions
of state welfarism. The West's new piety demands that universities return
to their pre-twentieth-century condition in which religious belief could not
be seriously challenged;**** and Edinburgh University has agreed. Those who
hope British academics will help them explain controversial truths to the
public will hope in vain. Until the Edinburgh verdict is overturned, every
British academic will know he is not seriously free -- even in e-mail -- to
mention unpopular facts. Britons have liked to sing in the twentieth
century that they "never, never, never shall be slaves"; but their
universities
will now remain enslaved to American campus speech codes until Brand and
'The g
Factor' are vindicated.
Chapter 12
Population Differences in g:
Causal Hypotheses
The relationship of the g factor to a number of biological variables
and its relationship to the size of the white-black differences on various
cognitive tests (i.e., Spearman's hypothesis) suggests that the average
white-black difference in g has a biological component. Human races are
viewed not as discrete, or Platonic, categories, but rather as breeding
populations that, as a result of natural selection, have come to differ
statistically in the relative frequencies of many polymorphic genes. The
"genetic distances" between various pop-ulations form a continuous variable
that can be measured in terms of differences in gene frequencies. Racial
populations differ in many genetic characteristics, some of which, such as
brain size, have behavioral and psychometric correlates, particularly g.
What I term the default hypothesis states that the causes of the phenotypic
differences between contemporary populations of recent African and European
descent arise from the same genetic and environmental factors, and in
approximately the same magnitudes, that account for individual differences
within each population. Thus genetic and en-vironmental variances between
groups and within groups are viewed as essentially the same for both
populations. The default hypothesis is able to account for the present
evidence on the mean white-black difference in g. There is no need to invoke
any ad hoc hypothesis, or a Factor X, that is unique to either the black or
the white population. The environmental component of the average s
difference between groups is primarily attributable to a host of
microenvironmental factors that have biological effects. They result from
non-genetic variation in prenatal, perinatal, and neonatal conditions and
specific nutritional factors.
The many studies of Spearman's hypothesis using the method of correlated
vectors show a strong relationship between the g loadings of a great variety
of cognitive tests and the mean black-white differences on those tests. The
fact that the same g vectors that are correlated with W-B differences are
also correlated (and to about the same degree) with vectors composed of
various cognitive tests' correlations with a number of genetic, anatomical,
and physiological variables suggests that certain biological factors may be
related to the average black-white population difference in the level of g.
The degree to which of each of many different psychometric tests is
correlated with all of the other tests is directly related to the magnitude
of the test's g loading. What may stem surprising, however, is the fact that
the degree to which a given test is correlated with any one of the following
variables is a positive function of that test's s loading:
Hereditability of test scores
Amount of inbreeding depression of test scores.
Heterosis (hybrid vigor, that is, raised test scores, due to outbreeding).
Head size (also, by inference, brain size).
Average evoked potential (AEP) habituation and complexity.
Glucose metabolic rate as measured by PET scan.
Average reaction time to elementary cognitive tasks
Size of The mean W-B difference on various cognitive tests.
The one (and probably the only) common factor that links all of these non-
psychometric variables to psychometric test scores and also links
psychometric test scores to the magnitude of the mean W-B difference is the
s factor. The critical role of g in these relationships is shown by the fact
that the magnitude of a given test's correlation with any one of the
above-listed variables is cor-related with the magnitude of the W-B
difference on that test. For example, Rushton"' reported a correlation (r =
+-.48) between the magnitudes of the mean W-B differences (in the American
standardization sample) on eleven subtests of the WISC-R and the effect of
inbreeding depression on the eleven subtest scores of the Japanese version
of the WISC. Further, the subtests' 6 loadings in the Japanese data
predicted the American W-B differences on the WISC-R sub-tests with r =
.69-striking evidence of the 6 factor's robustness across different
cultures. Similarly, the magnitude of the mean W-B difference on each of
sev-enteen diverse psychometric tests was predicted (with r = .71, p < .01)
by the tests' correlations with head size (a composite measure of length,
width, and circumference)."
This association of psychometric tests' g loadings, the tests'
correlations with genetic and other biological variables, and the mean W-B
differences in test scores cannot be dismissed as happenstance. The failure
of theories of group
420
differences in IQ that are based exclusively on attitudinal, cultural, and
experiential factors to predict or explain such findings argues strongly
that biological factors, whether genetic or environmental in origin, must be
investigated. Before examining possible biological factors in racial
differences in mental abilities, however, we should be conceptually clear
about the biological meaning of the term "race."
THE MEANING OF RACE
Nowadays one often reads in the popular press (and in some
anthropology
textbooks) that the concept of human races is a fiction (or, as one
well-known anthropologist termed it, a "dangerous myth"), that races do not
exist in reality, but are social constructions of politically and
economically dominant groups for the purpose of maintaining their own status
and power in a society. It naturally follows from this premise that, since
races do not exist in any real, or biological,
sense, it is meaningless even to inquire about the biological basis of any
racial
differences. I believe this line of argument has five main sources, none of
them scientific:
Heaping scorn on the concept of race is deemed an effective way of
combating racism-here defined as the belief that individuals who visibly
differ in certain characteristics deemed "racial" can be ordered on a
dimension of "human worth" from inferior to superior, and that therefore
various civil and political rights, as well as social privileges, should be
granted or denied according to a person's supposed racial origin.
Neo-Marxist philosophy (which still has exponents in the social sciences and
the popular media) demands that individual and group differences in
psychologically and socially significant traits be wholly the result of
economic inequality, class status, or the oppression of the working classes
in a capitalist society. It therefore excludes consideration of genetic or
biological factors (except those that are purely exogenous) from any part in
explaining behavioral differences among humans. It views the concept of race
as a social invention by those holding economic and political powers to
justify the division and oppression of unprivileged classes.
* The view that claims that the concept of race (not just the misconceptions
about it) is scientifically discredited is seen as a way to advance more
harmonious relations among the groups in our society that are commonly
perceived as "racially" different.
* The universal revulsion to the Holocaust, which grew out of the racist
doctrines of
Hitler's Nazi regime, produced a reluctance on the part of democratic
societies to sanction any inquiry into biological aspects of race in
relation to any behavioral variables, least of all socially important ones.
* Frustration with the age-old popular wrong-headed conceptions about race
has led some
experts in population genetics to abandon the concept instead of attempting
candidly to make the public aware of how the concept of race is viewed by
most present-day scientists.
Wrong Conceptions of Race. The root of most wrong conceptions of
race
is the Platonic view of human races ;is distinct types, that is, discrete,
mutually
421
exclusive categories. According to this view, any observed variation among
the members of a particular racial category merely represents individual
deviations from the archetype, or ideal type, for that "race." Since,
according to this Platonic view of race, every person can be assigned to one
or another racial
category, it naturally follows that there is some definite number of races,
each with its unique set of distinctive physical characteristics, such as
skin color, hair texture, and facial features. The traditional number has
been three: Caucasoid,
Mongoloid, and Negroid, in part derived from the pre-Darwinian creationist
view that "the races of mankind" could be traced back to the three
sons of
Noah-Shem, Ham, and Japheth.
The Cause of Biological Variation. All that is known today about the
world wide geographic distribution of differences in human physical
characteristics can be understood in terms of the synthesis of Darwinian
evolution and population genetics developed by R. A. Fisher, Sewall Wright,
Theodosius Dobzhansky, and Ernst Mayr. Races are defined in this context as
breeding populations that differ from one another in gene frequencies and
that vary in a number of intercorrelated visible features that are highly
heritable.
Racial differences are a product of the evolutionary process working
on the human genome, which consists of about 100,000 polymorphic genes (that
is, genes that contribute to genetic variation among members of a species)
located in the twenty-three pairs of chromosomes that exist in every cell of
the human body. The gents, each with its own locus (position) on a
particular chromosome, contain all of the chemical information needed to
create an organism. In addition to the polymorphic genes, there are also a
great many other gents that are not polymorphic (that is, are the same in
all individuals in the species) and hence do not contribute to the normal
range of human variation. Those genes that do product variation are called
polymorphic genes, as they have two or more different forms called alleles,
whose codes differ in their genetic information. Different alleles,
therefore, produce different effects on the phenotypic characteristic
determined by the gene at a particular chromosomal locus. Genes that do not
have different alleles (and thus do not have variable phenotypic effects)
are said to have gone to fixation; that is, alternative alleles, if any,
have long since been eliminated by natural selection in the course of human
or mammalian evolution. The physiological functions served by most basic
"housekeeping" genes are so crucial for the organism's development and
viability that almost any mutation of them proves lethal to the individual
who harbors it; hence only one form of the gene is possessed by all members
of a species. A great many such essential genes are in fact shared by
closely related species; the number of genes that are common to different
species is inversely related to the evolutionary distance between them. For
instance, the two living species closest to Homo sapiens in evolutionary
distance, chimpanzees and gorillas, have at least 97 percent of their genes
(or total genetic code) in common with present-day humans, scarcely less
than chimps and gorillas have in common with each other. This means that
even the very small percentage of genes (<3 percent) that differ between
humans and
422
the great apes is responsible for all the conspicuous and profound
phenotypic
differences observed between apes and humans. The genetic difference appears
small only if viewed on the scale of differences among all animal species.
New alleles created by mutation are subject to pleural natural
selection according to the degree of fitness they confer in a particular
environment. Changed environmental conditions can alter the selection
pressure for a certain allele, depending on the nature of its phenotypic
expression, thereby either increasing or decreasing its frequency in a
breeding population. Depending on its fitness in a given environment, it may
go to extinction in the population or it may go to fixation
(with every member of the population eventually possessing the allele).'
Many polymorphic gene loci harbor one or another allele of a balanced
polymorphism where in two or more alleles with comparable fitness values (in
a particular
environment) are maintained at equilibrium in the population. Thus
spontaneous genetic mutation and recombination, along with differential
selection of new alleles according to how their phenotypic expression
affects inclusive fitness, are crucial mechanisms of the whole evolutionary
process. The variation in all inherited human characteristics has resulted
from this process, in combination with random changes caused by genetic
drift and gene frequency changes caused by migration and intermarriage
patterns.
Races as Breeding Populations with Fuzzy Boundaries. Most
anthropologists and population geneticists today believe that the
preponderance of evidence from both the dating of fossils and the analysis
of the geographic distribution of many polymorphic genes in present-day
indigenous populations argues that genus Homo originated in Africa.
Estimates are that our direct distant hominid precursor split off from the
great apes some four to six million years ago. The consensus of human
paleontologists (as of 1997) accept the following basic scenario of human
evolution.
Austropalithecus afarensiss was a small (about 3'6"), rather
apt-like hominid
that appears to have been ancestral to all later hominids. It was bipedal,
walking more or less upright, and had a cranial capacity of 350 to 520 cm'
(about the same as that of the chimpanzee, but relatively larger for its
overall body size). Branching from this species were at least two lineage's,
one of which led to a new genus, Homo.
Homo also had several branches (species). Those that were precursors
of modern humans include HOMO habilis, which lived about 2.5 to I .5 million
years ago. It used tools and even made tools, and had a cranial capacity of
510 to 750 cm3 (about half the size of modern humans). Homo erectus lived
about 1.5 to 0.3 million years ago and had a cranial capacity of 850 to 1100
cm'
(about three-fourths the size of modern humans). The first hominid whose
fossil remains have been found outside .4frica. Homo erectus. migrated as
far as the Middle East, Europe, and Western and Southeastern Asia. No Homo
erectus remains have been found in Northern Asia, whose cold climate
probably was too severe for their survival skills.
Homo sapiens branched off the Homo erectus line in Africa at least
100 thousand years ago. During a period from about seventy to ten thousand
years ago they spread from Africa to the Middle East, Europe, all of Asia,
Australia,
and North and South America. To distinguish certain archaic subspecies of
Homo sapiens (e.g., Neanderthal man) that became extinct during this period
from their contemporaries who were anatomically modern humans, the latter
are now referred to as Homo sapiens sapiens (or Homo s. sapiens); it is this
line that branched off Homo erectus in Africa and spread to every continent
during the last 70.000 years. These prehistoric humans survived as foragers
living in small groups that frequently migrated in starch of food.
GENETIC DISTANCE
As small populations of Homo s. sapiens separated and migrated
further away from Africa, genetic mutations kept occurring at a constant
rate, as occurs in all living creatures. Geographic separation and climatic
differences, with their different challenges to survival, provided an
increasingly wider basis for populations to become genetically
differentiated through natural selection. Genetic mutations that occurred
after each geographic separation of a population had taken place were
differentially selected in each subpopulation according to the fitness the
mutant gent conferred in the respective environments. A great many mutations
and a lot of natural selection and genetic drift occurred over the course of
the five or six thousand generations that humans were gradually spreading
over the globe.
The extent of genetic difference, termed genetic distance, between
separated populations provides an approximate measure of the amount of time
since their separation and of the geographic distance between them. In
addition to time and distance, natural geographic hindrances to gene flow
(i.e., the interchange of genes between populations), such as mountain
ranges, rivers, seas, and deserts, also restrict gene flow between
populations. Such relatively isolated groups are termed breeding
populations, because a much higher frequency of mating occurs between
individuals who belong to the same population than occurs between
individuals from different populations. (The ratio of the frequencies of
within/ between population matings for two breeding populations determines
the degree of their genetic isolation from one another.) Hence the combined
effects of geographic separation, genetic mutation, genetic drift, and
natural selection for fitness in different environments result in population
differences in the frequencies of different alleles at many gene loci.
There are also other causes of relative genetic isolation resulting
from language differences as well as from certain social, cultural, or
religious sanctions against persons mating outside their own group. These
restrictions of gene flow may occur even among populations that occupy the
same territory. Over many generations these social forms of genetic
isolation produce breeding populations (including certain ethnic groups)
that evince relatively slight differences in allele frequencies from other
groups living in the same locality.
When two or more populations differ markedly in allele frequencies
at a great many gene loci whose phenotypic effects visibly distinguish them
by a particular configuration of physical features, these populations are
called subspecies. Virtually every living species on earth has two or more
subspecies. The human species is no exception, but in this case subspecies
are called races. Like all other subspecies, human races are interfertile
breeding populations whose individuals differ on average in distinguishable
physical characteristics.
Because all the distinguishable breeding populations of modern humans were
derived from the same evolutionary branch of the genus HOMO, namely homo s.
sapiens, and because breeding populations have relatively permeable (non
biological) boundaries that allow gene how between them, human races can be
considered as genetic "fuzzy sets." That is to say, a race is one of a
number of statistically distinguishable groups in which individual
membership is not mutually exclusive by any single criterion, and
individuals in a given group differ only statistically from one another and
from the group's central tendency on each of the many imperfectly correlated
genetic characteristics that distinguish between groups as such. The
important point is that the average difference on all of these
characteristics that differ among individuals with the group is less than
the average difference between the groups on these genetic characteristics
What is termed a dine results where groups overlap at their fuzzy
boundaries in some characteristic, with intermediate gradations of the
phenotypic characteristic, often making the classification of many
individuals ambiguous or even
impossible, unless they are classified by some arbitrary rule that ignores
biology. The fact that there are intermediate gradations or blends between
racial groups, however, does not contradict the genetic and statistical
concept of race. The different colors of a rainbow do not consist of
discrete bands but are a perfect
continuum, yet we readily distinguish different regions of this continuum as
blue, green, yellow, and red, and we effectively classify many things
according to these colors. The validity of such distinctions and of the
categories based on them obviously need not require that they form perfectly
discrete Platonic categories.
It must be emphasized that the biological breeding populations
called races can only be defined statistically, as populations that differ
in the central tendency (or mean) on a large number of different
characteristics that are under some degree of genetic control and that are
correlated with each other through descent from common ancestors who are
relatively recent in the time scale of evolution (i.e., those who lived
about ten thousand years ago, at which time all of the continents and most
of the major islands of the world were inhabited by relatively isolated
breeding populations of Homo s. sapiens).
Of course, any rule concerning the number of gene loci that must
show differences in allele frequencies (or any rule concerning the average
size of differences in frequency) between different breeding populations for
them to be considered races is necessarily arbitrary, because the
distribution of average absolute differences in allele frequencies in the
world's total population is a
426
perfectly continuous variable. Therefore, the number of different
categories, or races, into which this continuum can be divided is, in
principle, wholly arbitrary, depending on the degree of genetic difference a
particular investigator chooses as the criterion for classification or the
degree of confidence one is willing to accept with respect to correctly
identifying the area of origin of one's ancestors.
Some scientists have embraced all of Homo sapiens in as few as two
racial categories, while others have claimed as many as seventy. These
probably represent the most extreme positions in the "lumper" and "splitter"
spectrum.
Logically, we could go on splitting up groups of individuals on the basis of
their genetic differences until WE reach each pair of monozygotic twins,
which are genetically identical. But as any pair of MZ twins are always of
the same
sex, they of course cannot constitute a breeding population. (If
hypothetically they could, the average genetic correlation between all of
the offspring of any pair of MZ twins would be 2/3; the average genetic
correlation between the offspring of individuals paired at random in the
total population is 1/2; the offspring of various forms of genetic
relatedness, such as cousins [a preferred match in some parts of the world],
falls somewhere between 2/3 and 1/2.) However, as I will explain shortly,
certain multivariate statistical methods can provide objective criteria for
deciding on the number and composition of different racial groups that can
be reliably determined by the given genetic data or that may be useful for a
particular scientific purpose. But one other source of genetic variation
between populations must first be explained.
Genetic Drift. In addition to mutation, natural selection, and
migration, another means by which breeding population may differ in allele
frequencies is through a purely stochastic (that is, random) process termed
genetic drift. Drift is most consequential during the formation of new
populations when their numbers are still quite small. Although drift occurs
for all gene loci, Mendelian characters (i.e., phenotypic traits), which are
controlled by a single gene locus, are more noticeably affected by drift
than are polygenic traits (i.e., those caused by many genes). The reason is
purely statistical.
Changes in a population's allele frequencies attributable to genetic
drift can
be distinguished from changes due to natural selection for two masons: (1)
Many genes are neutral in the sense that their allele frequencies have
remained unaffected by natural selection, because they neither increase nor
decrease fitness; over time they move across the permeable boundaries of
different breeding
populations. (2) When a small band of individuals emigrates from the
breeding population of origin to found a new breeding population, it carries
with it only a random sample of all of the alleles, including neutral
alleles, that existed in the entire original population. That is, the allele
frequencies at all gene loci in the migrating band will not exactly match
the allele frequencies in the original
population. The band of emigrants, and of course all its descendants (who
may eventually form a large and stable breeding population), therefore
differs genetically from its parent population as the result of a purely
random process. This random process is called founder effect. It applies to
all gene loci. All during the time that genetic drift was occurring, gene
mutations steadily continued, and natural selection continued to product
changes in allele frequencies at many loci. Thus the combined effects of
genetic drift, mutation, and natural selection ensure that a good many
alleles are maintained at different frequencies in various relatively
isolated breeding populations. This process did not happen all at once and
then cease. It is still going on, but it takes place too slowly to be
perceived in the short time span of a few generations.
It should be noted that the phenotypic differences between
populations that were due to genetic drift are considerably smaller than the
differences in those phenotypic characteristics that were strongly subject
to natural selection, especially those traits that reflect adaptations to
markedly different climatic conditions, such as darker skin color (thought
to have evolved as protection from the tropical sun's rays that can cause
skin cancer and to protect against folate decomposition by sunlight), light
skin color (to admit more of the ultraviolet rays needed for the skin's
formation of vitamin D in northern regions; also because clothing in
northern latitudes made dark skin irrelevant selectively and it was lost
through random mutation and drift), and globular versus elongated body shape
and head shape (better to conserve or dissipate body heat in cold or hot
climates, respectively).'
Since the genetic drift of neutral genes is a purely random process,
and given
a fairly constant rate of drift, the differing allele frequencies of many
neutral
genes in various contemporary populations can be used as a genetic clock to
determine the approximate time of their divergence. The same method has been
used to estimate the extent of genetic separation, termed genetic distance,
between populations.
Measurement and Analysis of Genetic Distance between Groups.
Modern genetic technology makes it possible to measure the genetic distance
between different populations objectively with considerable precision, or
statistical reliability. This measurement is based on a large number
of genetic polymorphisms for what are thought to be relatively neutral
genes, that is, genes whose allele frequencies therefore differ across
populations more because of mutations and genetic drift than be cause of
natural selection. Population allele frequencies can be as low as zero or
as high as 1.0 (as there are certain alleles that have large frequencies in
some populations but are not found at all in other populations). Neutral
genes are preferred in this work be cause they provide a more stable and
accurate evolutionary "clock" than do genes whose phenotypic characters
have been subjected to the kinds of diverse external conditions that are the
basis for natural selection. Although neutral genes provide a more accurate
estimate of populations' divergence times, it should be noted that, by
definition, they do not fully reflect the magnitude of genetic differences
between populations that are mainly attributable to natural selection.
The technical rationale and formulas for calculating genetic
distance are fully
explicated elsewhere. For present purposes, the genetic distance, D, between
two groups can be thought of here simply as the average difference in
allele
428
frequencies between two populations, with D scaled to range from zero (i.e.,
no allele differences) to one (i.e., differences in all alleles). One can
also think of D as the complement of the correlation coefficient r (i.e., D
= I - r, and r = I - D). This conversion of D to r is especially useful,
because many of the same objective multivariate statistical methods that
were originally devised to analyze large correlation matrices (e.g.,
principal components analysis, factor analysis. hierarchical cluster
analysis, multidimensional scaling) can also be used to analyze the total
matrix of genetic distances (although they are converted to correlations)
between a large number of populations with known allele frequencies based on
some large number of genes.
The most comprehensive study of population differences in allele
frequencies
to date is that of the Stanford University geneticist Luigi Luca
Cavalli-Sforza and his co-workers.".' Their recent 1046-page hook reporting
the detailed results of their study is a major contribution to the science
of population genetics. The main analysis was based on blood and tissue
specimens obtained from representative samples of forty-two populations,
from every continent (and the Pacific
islands) in the world. All the individuals in these samples were aboriginal
OI indigenous to the areas in which they were selected samples; their
ancestors have lived in the same geographic area since no later than 1492, a
familiar date that generally marks the beginning of extensive worldwide
European explorations and the consequent major population movements. In each
of the Stanford
study's population samples, the allele frequencies of 120 alleles at
forty-nine gene loci were determined. Most of these genes determine various
blood groups,
enzymes, and proteins involved in the immune system, such as human
lymphocyte antigens (HLA) and immunoglobulins. These data were then used to
calculate the genetic distance (D) between each group and every other group.
(DNA sequencing was also used in separate analyses of some groups; it yields
finer genetic discrimination between certain groups than can the genetic
polymorphisms used in the main analysis.) From the total matrix of (42 X
41)/2 = 861
D values, Cavalli-Sforza et al. constructed a genetic linkage tree. The D
value between any two groups is represented graphically by the total
length of the
line that connects the groups in the branching tree. (Set Figure 12.1.)
The greatest genetic distance, that is, the largest D, is between
the five African
groups (listed at the top of Figure 12.1) and all the other groups. The next
largest D is between the Australian + New Guinean groups and the remaining
other groups; the next largest split is between the South Asians + Pacific
Islanders and all the remaining groups, and so on. The clusters at the
lowest level
(i.e., at far right in Figure 12.1) can also be clustered to show the D
values between larger groupings, as in Figure 12.2. Note that these clusters
product much the same picture as the traditional racial classifications that
were based on skeletal characteristics and the many visible physical
features by which nonspecialists distinguish "races."'
It is noteworthy, but perhaps not too surprising, that the grouping
of various human populations in terms of invisible genetic
polymorphisms for many relatively
¦-------------------.---------------------------------San (Bushmen)
¦ ¦ __________________ Mbuli Pygmy
¦ ¦ ¦ __+------Bantu
¦ ¦---¦-------------------¦ ¦ -----Nilotic
¦ ¦---¦ ¦----¦------W African
¦ ¦------------------------- Ethiopian
¦ ¦---------------------SE Indian
¦ ¦------------¦ ¦-----------------Lapp
¦ ¦ ¦--¦ ¦--------------Berber
¦ ¦ ¦--¦ ¦-----------Sardinian
¦ ¦ ¦--¦ ¦----------Indian
-¦ ¦ ¦--¦ ¦--------SW Asian
¦ ¦ ¦ ¦ ¦---+--Iranian
¦ ¦---¦ ¦--¦ ¦-Greek
¦ ¦ ¦ ¦__ ¦----Basque
¦ ¦ ¦ ¦--¦---Italian
¦ ¦ ¦ ¦-¦--Danish
¦ ¦ ¦ ¦-English
¦ ¦ ¦
¦ ¦ ¦ ¦---------Samoyed
¦ ¦ ¦ ¦--------¦--------Mongol
¦ ----¦ ¦ ¦-------¦ .------Tibetan
¦ ¦ ¦ ¦ ¦ ¦ ¦------¦___¦--Korean
¦ ¦ ¦ ¦ ¦-----¦ ¦---¦ ¦--Japanese
¦ ¦ ¦ ¦ ¦ ¦ ¦-----------Ainu
¦ ¦ ¦ ¦ ¦ ¦ ¦-----------------------N. Turkic
¦ ¦ ¦ ¦ ¦ ¦---¦-------+_______ Eskimo
¦ ¦ ¦ ¦ ¦ ¦------------Chukchi
¦ ¦ ¦ ¦ ¦
¦ ¦ ¦ ¦__¦ ¦------------S Amerind
¦ ¦ ¦ ¦ ¦-----+---¦---------C Amerind
¦ ¦ ¦ ¦---------¦ ¦------------ N Amerind
¦ ¦ ¦ ¦___________N.W. American
¦ ¦ ¦
¦ ¦ ¦ ¦------¦----------S Chinese
¦ ¦ ¦ ¦ ¦--------¦--Mon Khymer
¦ ¦ ¦ ¦-¦ ¦--Thai
¦ ¦ ¦ ¦-----¦ ¦-----¦-------------Indonesian
¦ ¦ ¦ ¦ ¦ ¦_______Philipline
¦ ¦ ¦----------------¦ ¦------------------Malaysian
¦ ¦ ¦----¦---------------------Polynesian
¦ ¦ ¦ ¦---------------Micronesian
¦ ¦
¦----+---------------------Melaesian
¦ ¦
¦ ¦ ¦--------------------------------New Guinean
¦-----------¦----------¦___________________ Australian
Genetic Distance---------------------------?
Fig 12.11 Genetic Distance
. The genetic linkage tree for forty-two populations. The genetic distance
between any two groups is represented by the total length of the line
separating them.
(Cavalli-Sforza, L. L., Menozzi, P. & Piazza, A., The history and geography
of human
genes. Copyright @ 1994 by Princeton University Press. Reprinted by
permission of Princeton University Press.)
¦------------------African
¦
¦ ____¦----------- Caucasoid
¦ ¦ ¦
¦ ¦ ¦ ¦---¦--North east
Asia
¦ ¦---¦ ¦____¦ ¦--Arctic Asia
¦--------------------------------------¦ ¦ ¦___America
¦ ¦-------------------Southeast
Asia
¦____________ New Guinea &
Australia
Fig. 12.2. A linkage tree based on the average genetic distances between the
major clusters among the groups shown in Figure 12.1. (Cavalli-Sforza, L.
L., Menozzi, P. & Piaza, A., T., The history and geography of human genes.
Copyright @ 1994 by Princeton University
African-Americans. The first Africans arrived in North America in
1619 and for more than two centuries thereafter, mostly between 1700 and
1800, the
432
majority of Africans were brought to America as slaves. The end to this
involuntary migration came between 1863 and 1865, with the Emancipation
Proclamation. Nearly all of the Africans who were enslaved came from
sub-Sahara11 West Africa, specifically the coastal region from Senegal to
Angola. The populations in this area are often called West African or North
West and Central West Bantu.'"'
Steadily over time, the real, but relatively low frequency of
cross-mating between blacks and whites produced an infusion of Caucasoid
genes into the black gene pool. As a result, the present-day population of
black Americans is
genetically different from the African populations from whom they descended.
Virtually 100 percent of contemporary black Americans have some Caucasian
ancestry. Most of the Caucasian genes in the present day gene pool of black
Americans entered the black gene pool during the period of slavery.
Estimates of the proportion of Caucasoid genes in American blacks
are based on a number genetic polymorphisms that have fairly high allele
frequencies in the European population but zero or near zero frequencies in
the West African population. or vice versa. For any given allele, the
estimated proportion (M) of white European ancestry in American blacks is
obtained by the formula M =(qb - qaf)/(qw - qaf) where qb is the given
allele's frequency in the black
American population, qaf is its frequency in the African population, and q,
is its frequency in the white European population. The average value of M is
obtained over each of twenty or so genes with alleles that are unique either
to Africans or to Europeans. The largest studies, which yield estimates with
the greatest precision, p(Give mean values of M close to 25 percent, with a
standard error of about 3percent. This is probably the best estimate
for the African-American population overall. However, M varies across
different regions of the United States, being as low as 4 percent to 10
percent in some southeastern States and spreading out in a fan-shaped
gradient toward the north and the west to reach over 40 percent in some
northeastern and northwestern states. Among the most typical and precise
estimates of M are those for Oakland, California (22.0 percent) and
Pittsburgh, Pennsylvania (25.2 percent). This regional variation in M
reflects the pattern of selective migration of blacks from the Deep South
since the mid-nineteenth century. Gene flow, of course, goes in both
directions. In every generation there has been a small percentage of persons
who have some African ancestry but whose ancestry is predominantly Caucasian
and who permanently "pass as white." The white American gene pool
therefore contains some genes that can be traced to Africans who were
brought over as slaves (estimated by analysts of genetic polymorphisms to be
less than 1 percent).""
Genetic Distance and Population Differences in g. The preceding
discourse on the genetics of populations is germane to any discussion of
population differences in g. The differences in gene frequencies that
originally created different breeding populations largely explain the
physical phenotypic differences observed between populations called races.
Most of these differences in visible phenotypic characteristics are the
result of natural selection working over the course of human evolution.
Selection changes gene frequencies in a population by acting directly on any
genetically based phenotypic variation that affects Darwinian fitness for a
given environment. This applies not only to physical characteristics, but
also to behavioral capacities, which are necessarily to some degree a
function of underlying physical structures. Structure and function are
intimately related, as their evolutionary origins are inseparable.
The behavior-al capacities or traits that demonstrate genetic
variation can also be viewed from an evolutionary perspective. Given the
variation in allele frequencies between populations for virtually every
known polymorphic gene, it is exceedingly improbable that populations do not
differ in the alleles that affect the structural and functional basis of
heritable behavioral traits. The empirical generalization that every
polygenic physical characteristic that shows differences between individuals
also shows mean differences between populations applies to behavioral as
well as physical characteristics. Given the relative genetic distances
between the major racial populations, one might expect some behavioral
differences between Asians and Europeans to be of lesser magnitude than
those between these groups and sub-Saharan Africans. .
The behavioral, psychological, or mental characteristics that show
the highest
g loadings are the most heritable and have the most biological correlates
(see Chapter 6) and are therefore the most likely to show genetic population
differences
. Because of the relative genetic distances, they are also the most likely
to show such differences between Africans (including predominantly African
descendants) and Caucasians or Asians.
Of the approximately 100,000 human polymorphic genes, about 50,000
are functional in the brain and about 30,000 are unique to brain functions."
The brain is by far the structurally and functionally most complex organ in
the human body and the greater part of this complexity resides in the neural
structures of the cerebral hemispheres, which, in humans, are much larger
relative to total brain size than in any other species. A general principle
of neural organization states that, within a given species, the size and
complexity of a structure reflect the behavioral importance of that
structure. The reason, again, is that structure and function have evolved
conjointly as an integrated adaptive mechanism. But as there are only some
50,000 genes involved in the brain's development and there are at least 200
billion neurons and trillions of synaptic connections in the brain, it is
clear that any single gene must influence some huge number of neurons not
just any neurons selected at random, but complex systems of neurons
organized to serve special functions related, to behavioral capacities.
It is extremely improbable that the evolution of racial differences
since the advent Homo Sapiens excluded allelic changes only in those 50,000
gents that are involved with the brain.
Brain size has increased almost threefold during the course of human
evolution, from about 500 cm' in the Australopithecenes to about 1,350 cm3
(the present estimated worldwide average) in Homo sapiens. Nearly all of
this in
434
crease in brain volume has occurred in connection with those parts of the
cerebral hemispheres associated with cognitive processes, particularly the
prefrontal lobes and the posterior association areas, which control
foresight, planning, goal directed behavior, and the integration of sensory
information required for higher levels of information processing. The parts
of the brain involved in vegetative and sensorimotor functions per se differ
much less in size, relative to total brain
size, even between humans and chimpanzees than do the parts of the brain
that subserve cognitive functions. Moreover, most of the evolutionary
increase in brain volume has resulted not from a uniform increase in the
total number of cortical neurons per se, but from a much greater increase in
the number and complexity of the interconnections between neurons, making
possible a higher level of interneuronal communication on which complex
information processing depends. Although the human brain is three times
larger than the chimpanzee brain, it has only 1.25 times as many neurons;
the much greater difference is in their degree of arborization, that is,
their number of synapses and interconnecting branches.
No other organ system has evolved as rapidly as the brain of Homo
sapiens,
a species that is unprecedented in this respect. Although in hominid
evolution there was also an increase in general body size, it was not nearly
as great as the increase in brain size. In humans, the correlation between
individual differences in brain size and in stature is only about +.20. One
minus the square of this relatively small correlation, which is .96,
reflects the proportion of the total variance in brain size that cannot be
accounted for by variation in overall body size. Much of this residual
variance in brain size presumably involves cognitive functions.
Bear in mind that, from the standpoint of natural selection, a
larger brain
size (and its corresponding larger head size) is its many ways decidedly
disadvantageous. A large brain is metabolically very expensive, requiring a
high calorie diet. Though the human brain is less than 2 percent of total
body weight, it accounts for some 20 percent of the body's basal metabolic
rate (BMR). In other primates, the brain accounts for about 10 percent of
the BMR, and for most carnivores, less than 5 percent. A larger head also
greatly increases the difficulty of giving birth and incurs much
greater risk of perinatal trauma or even fetal death, which are much more
frequent in humans than in any other animal species. A larger head also puts
a greater strain on the skeletal and muscular support. Further, it
increases the chances of being fatally hit by an enemy's club or missile.
Despite such disadvantages of larger head size, the human brain, in fact,
evolved markedly in size, with its cortical layer accommodating to a
relatively lesser increase in head size by becoming highly convoluted in the
endocranial vault. In the evolution of the brain, the effects of natural
selection had to have reflected the net selective pressures that made an
increase in brain size disadvantageous versus those that were advantageous.
The advantages obviously outweighed the disadvantages to some degree or the
increase in hominid brain size would not have occurred.
I
The only conceivable advantage to an increase in the size and
complexity of the brain is the greater behavioral capacity this would
confer. This would include: the integration of sensory information, fine
hand-eye coordination, quickness of responding or voluntary response
inhibition and delayed reaction depending on the circumstances, perceiving
functional relationships between two things when only one or neither is
physically present, connecting past and future events, learning from
experience, generalization, far transfer of learning, imagery,
intentionality and planning, short-term and long-term memory capacity,
mentally manipulating objects without need to handle them physically,
Foresight, problem solving, use of denotative language in vocal
communication, as well as all of the information processes that are inferred
from performance on what were referred to in Chapter 8 as "elementary
cognitive tasks." These basic information processes are involved in coping
with the natural exigencies and the contingencies of humans' environment. An
increase in these capabilities and their functional efficiency are, in fact,
associated with allometric differences in brain size between various species
of animals, those with greater brain volume in relation to their overall
body size generally displaying more of the kinds of capabilities listed
above.1'31 The functional efficiency of the various behavioral capabilities
that are common to all members of a given species can be enhanced
differentially by natural selection, in the same way (though probably not to
the same degree) that artificial selection has made dogs of various breeds
differ in propensities and trainability for specific types of behavior.'"
What kinds of' environmental pressures encountered by Homo erectus and early
Homo sapiens would have selected for increased size and complexity of the
brain? Evolutionists have proposed several plausible scenarios. Generally,
a more complex brain would be advantageous in hunting skill, cooperative
social interaction, and the development of tool use, followed by the
higher-order skill of using tools to make other tools, a capacity possessed
by no contemporary species other than Homo sapiens.
The environmental forces that contributed to the differentiation of'
major populations and their gene pools through natural selection were mainly
climatic, but parasite avoidance and resistance were also instrumental. Homo
sapiens evolved in Africa from earlier species of Homo that originated
there. In migrating from Africa and into Europe and Asia, they encountered
highly diverse climates. These migrants, like their parent population that
remained in sub-Saharan Africa, were foragers, but they had to forage for
sustenance under the highly different conditions of their climatically
diverse habitats. Foraging was possible all during the year in the tropical
and subtropical climates of equatorial regions, while in the more northern
climate of Eurasia the abundance of food that could be obtained by hunting
and gathering greatly fluctuated with the seasons. This necessitated the
development of more sophisticated techniques for hunting large game,
requiring vocal communication and cooperative efforts (e.g., by ambushing,
trapping. or corralling), along with foresight in planning a head for
the preservation, storage, and rationing of food in order to survive the
severe winter
436
months when foraging is practically impossible. Extreme seasonal changes and
the cold climate of the northern regions (now inhabited by Mongoloids and
Caucasians) also demanded the ingenuity and skills for constructing more
permanent and sturdy dwellings and designin,0 substantial clothing to
protect against the elements. Whatever bodily and behavioral adaptive
differences between populations were wrought by the contrasting conditions
of the hot climate of sub-Saharan Africa and the cold seasons of northern
Europe and northeast Asia would have been markedly intensified by the last
glaciation, which occurred approximately 30,000 to 10,000 years ago, after
Homo .sapiens had inhabited most of the globe. During this long period of
time, large regions of the Northern Hemisphere were covered by ice and the
north Eurasian winters were far more severe than they have ever been For
over 10,000 years.
It seems most plausible, therefore, that behavioral adaptations of a
kind that could be described as complex mental abilities were more crucial
for survival of the populations that migrated to the northern Eurasian
regions, and were therefore under greater selection pressure as fitness
characters, than in the populations that remained in tropical or subtropical
regions.""
Climate has also influenced the evolution of brain size apparently
indirectly through its direct effect on head size, particularly the shape of
the skull. Head size and shape are more related to climate than is the body
as a whole. Because the human brain metabolizes 20 percent of the body's
total energy supply, it generates more heat in relation to its size than any
other organ. The resting rate of energy output of the average European adult
male's brain is equal to about three-fourths that of a 100-watt light bulb.
Because temperature changes in the brain of only four to five degrees
Celsius are seriously adverse to the normal functioning of the brain, it
must conserve heat (in a cold environment) or dissipate heat (in a hot
environment). Simply in terms of solid geometry, a sphere contains a larger
volume (or cubic capacity) for its total surface area than does than any
other shape. Conversely, a given volume can be contained in a sphere that
has a smaller surface area than can be contained by a nonspherical shape
with the same surface area (an elongated oval shape, for instance). Since
heat radiation takes place at the surface, more spherical shapes will
radiate less heat and conserve more heat for a given volume than a
nonspherical shape, and less spherical shapes will lose more heat by
radiation. Applying these geometric principles to head size and shape, one
would predict that natural selection would favor a smaller head with a less
spherical (dolichocephalic) shape because of its better heat dissipation in
hot climates, and would favor a more spherical (brachycephalic) head to
accommodate a larger volume of brain matter with a smaller surface area
because of its better heat conservation in cold climates.
(The dolichocephalic-brachycephalic dimension is related to the head's
width: Length ratio, known as the cephalic index.) In brief, a smaller,
dolichocephalic cranium is advantageous for thermoregulation of the brain in
a hot climate, whereas a larger, brachycephalic cranium is advantageous in a
cold climate. In
437
the world's populations, head breadth is correlated about +.8 with cranial
capacity; head length is correlated about +.4.
Evidence that the average endocranial volume of various populations
is related
to cranial shape and that both phenomena are, in some part, adaptations to
climatic conditions in different regions has been shown by physical
anthropologist Kenneth Beals and his co-workers. i They amassed measurements
of endocranial volume in modern humans from some 20,000 individual crania
collected from every continent, representing 122 ethnically distinguishable
populations. They found that the bglobal mean cranial capacity for
populations in hot climates is 1,297 +- 10.5 cm'; for populations in cold
and temperate climate it is 1,386 +- 6.7 cm', a highly significant (p <
10-4") difference of 89 cm'. Beals also plotted a correlation scatter
diagram of the mean cranial capacity in cm' of each of 122 global
populations as a function of their distance from the equator (in absolute
degrees north or south latitude). The Pearson correlation between absolute
distance from the equator and cranial capacity was r = +.62 p < l0-5). (The
regression equation is: cranial capacity = 2.5 cm3 X Degrees
latitude1 + 1257.3 cm': that is, an average increase of 2.5 cm' in cranial
capacity for every 1 degree increase in latitude.) The same analysis applied
to populations of the African-Eurasian landmass showed a cranial capacity X
latitude correlation of +.76 (17 < 10-4) and a regression slope of 3.1 cm'
increase in cranial capacity per every 1degree of absolute latitude in
distance from the equator. The indigenous populations of North and South
American continents show a correlation of +.44 and a regression slope of
1.5; the relationship of cranial capacity to latitude is less pronounced in
the New World than in the Old World, probably because Homo Sapiens inhabited
the New World much more recently, having migrated from Asia to North America
only about 15,000 years ago, while Homo Sapiens have inhabited the African
and Eurasian continents for a much longer period.
Are the climatic factors associated with population differences in cranial
capacity, as summarized in the preceding, section, reflected in the average
cranial
or brain-size measurements of the three broadest contemporary population
groups, generally termed Caucasoid (Europeans and their descendants),
Negroid
(Africans and descendants), and Mongoloid (Northeast Asians and
descendants)? A recent comprehensive review summarized the worldwide
literature on brain
volume in cm3 as determined from four kinds of measurements: (a) direct
measurement of the brain obtained by autopsy, (b) direct measurement of
endocranial volume of the skull, (c) cranial capacity estimated from
external head measurements, and (d) cranial capacity estimated from head
measurements and corrected for body size. The aggregation of data obtained
by different methods, based on large samples, from a number of studies tends
to average-out the sampling error and method effects and provides the best
overall estimates of the racial group
438
Table 12.1 Mean Cranial Capacity (cm") of Three Racial Populations
Determined from Four Types of Measurements
Measurement East Asian European African
Autopsy 1351 1356 1223
Endocranial volume 1415 1362 1268
External head measurements 1335 1341 1284
Corrected for body size 1356 1329 1294
Mean 1364 1347 1267
Source: Based on data summarized by Rushton & Ankney. 1996.
Other evidence of a systematic relationship between racial differences in
cranial capacity and IQ comes from an "ecological" correlation, which is
commonly used in epidemiological research. It is simply the Pearson r
between the
means of three or mom defined groups, which disregards individual variation
within the groups.Z" Referring back to Table 12.1, I have plotted the median
IQ of each of the three populations as a function of the overall mean
cranial capacity of each population. The median IQ is the median value of
all of the mean values of IQ reported in the world literature for Mongoloid,
Caucasoid, and Negroid
populations. (The source of the cranial capacity means for each group was
explained in connection with Table 12. 1 .) The result of this plot is shown
in Figure
12.4. The regression of median IQ on mean cranial capacity is almost
perfectly
linear, with a Pearson r = +.998. Unless the data points in Figure 12.4 are
themselves highly questionable, the near-perfect linearity of the regression
indicates that IQ can be regarded as a true interval scale. No mathematical
transformation of the IQ scale would have yielded a higher correlation. Thus
it appears that the central tendency of IQ for different populations is
quite accurately predicted by the central tendency of each population's
cranial capacity.
110 ¦
¦ . * m
¦ c .
100 ¦ . *
¦ .
¦ .
90 ¦ .
¦ .
¦ n .
80 ¦ . *
¦
¦
70 ¦
-------------------------------------------
1250 1300 1350 1400
Cranial Capacity (cm')
figure 12.4. Median IQ of three populations (Mongoloid, Caucasoid, and
Negroid) plotted as a function of the mean cranial capacity in each
population. (Regression: IQ = ,262 X cranial capacity- 252.6; r = ,998.)
CONTROLLING THE ENVIRONMENT :TRANSRACIAL ADOPTION
Theoretically, a transracial adoption study should provide a strong
test of the default hypothesis. In reality, however. a real-life adoption
study can hardly meet the ideal conditions necessary to make it definitive.
Such conditions can be perfectly met only through the cross-fostering
methods used in animal behavior genetics, in which probands can be randomly
assigned to foster parents. Although adoption in infancy is probably the
most comprehensive and powerful environmental intervention possible with
humans, under natural conditions the adoption design is unavoidably
problematic because the investigator cannot experimentally control the
specific selective factors that affect transracial adoptions-the adopted
children themselves, their biological parents, or the adopting parents.
Prenatal and perinatal conditions and the preadoption environment are
largely uncontrolled. So, too, is the willingness of parents to volunteer
their adopted children for such a study, which introduces an ambiguous
selection factor into the subject sampling of any adoption study. It is
known that individuals who volunteer as subjects in studies that involve the
measurement of mental ability generally tend to be somewhat above-average
in ability. For these reasons, and given the scarcity of transracial
adoptions, few such studies have been reported in the literature. Only one
of these, known as the Minnesota Transracial Adoption Study, is based on
large enough samples of black and white adoptees to permit statistical
analysis. While even the Minnesota Study dots not meet the theoretically
ideal conditions, it is nevertheless informative with respect to the default
hypothesis.
Initiated and conducted by Sandra Starr and several colleagues the Minnesota
Transracial Adoption Study examined the same groups of children when they
were about age 7 and again in a IO-year follow-up when they were about age
17. The follow-up study is especially important, because it has been found
in other studies that family environmental influences on IQ decrease from
early childhood to late adolescence, while there is a corresponding increase
in the phenotypic expression of the 3Ocnetic component of IQ variance.
Therefore, one would have more confidence in the follow-up data (obtained at
age 17) as a test of the default hypothesis than in the data obtained at age
7.
Four main groups were compared on IQ and scholastic performance:
1 Biological offspring of the white adoptive parents.
2. Adopted children whose biological father and mother were both white (WW).
3. Adopted interracial children whose biological fathers were black and
whose mothers
were white (BW).
4. Adopted children whose biological father and mother were both black (BB).
(A group of twelve children, consisting of Asian and Amerindian adoptees who
took part in both the first study and the follow-up, were not included in
the main statistical analyses.)
The adoptive parents were all upper-middle class, employed in proffesional
and managerial occupations, with an average educational level of about
sixteen
years (college graduate) and an average WAIS IQ of about 120. The biological
parents of the BB and BW adoptees averaged 11.5 years and 12.5 years of
education, respectively. The IQs of the adoptees' biological parents were
not known. Few of the adoptees ever lived with their biological parents;
some lived briefly in foster homes before they were legally adopted. The
average age of adoption was 32 months for the BB adoptees, 9 months for the
BW adoptees, and 19 months for the WW adoptees. The adoptees came mostly
from the North Central and North Eastern regions of the United States. The
Stanford-Binet and the Wechsler Intelligence Scale for Children (WISC) were
used in the first study (at age seven), the Wechler Adult Intelligence Scale
(WAIS) was used in the follow-up study (at age seventeen).5z
The investigators hypothesized that the typical W-B IQ difference
results from the lesser relevance of the specific information content of IQ
tests to the blacks' typical cultural environment. They therefore suggest
that if black children were reared in a middle or upper-middle class white
environment they would perform near the white average on IQ tests and in
scholastic achievement. This cultural difference hypothesis therefore posits
no genetic effect on the mean W-B IQ difference; rather, it assumes equal
black and white means in genotypic g. The default hypothesis, on the other
hand, posits both genetic and environmental
factors as determinants of the mean W-B IQ difference. It therefore predicts
that groups of black and white children reared in highly similar
environments typical of the white middle-class culture would still differ in
IQ to the extent expected from the heritability of IQ within either
population.
The data of the Minnesota Study also allow another prediction based
on the default hypothesis, namely, that the interracial children (BW) should
score, on average, nearly (but not necessarily exactly) halfway between the
means of the WW and BB groups. Because the alleles that enhance IQ are
genetically dominant, we would expect the BW group mean to be slightly
closer to the mean of the WW group than to the mean of the BB group. That
is, the heterosis (outbreeding enhancement of the trait) due to dominance
deviation would raise the BW group's mean slightly above the midpoint
between the BB and WW groups. (This halfway point would be the expected
value if the heritability of IQ reflected only the effects of additive
genetic variance.) Testing this predicted heterotic effect is unfortunately
debased by the fact that the IQs of the biological parents of the BB and BW
groups were not known. As the BB biological parents
474
Table 12.5 IQ Mean and Standard Deviation of Groups in the Minnesota
Transracial Adoption Study Tested at Two Ages
Group Age 7 Age 17
N Mean SD Mean SD
Adoptive Father 74 121.7 9.5 117.1 11.5
Adoptive Mother 84 119.1 9.7 113.6 10.5
Biological Offspring 104 116.4 13.5 109.4 13.5
----------------------------------------------------------------------------
------------------------------------------------------
Adopted White (W/W) 16 117.6 11.3 105.6 14.9
Adopted Interracial(B/W) 55 109.5 11.9 98.5 10.6
Adopted Black (B/B) 21 95.4 13.3 89.4 11.7
"The number of individuals tested both in 1975 and 1986.
Source: Data from Weinberg et al., 1992.
had about one year less education than the BW parents, given the correlation
between IQ and education, it is likely that the mean IQ of the BB parents
was somewhat lower than the mean IQ of the BW parents, and so would produce
a result similar to that predicted in terms of heterosis. It is also
possible, though less likely, that the later age of adoption (by twenty-one
months) of the BB adoptees than of the BW adoptees would produce an effect
similar to that predicted in terms of heterosis.
The results based on the subjects who were tested on both occasions
are shown in Table 12.5. Because different tests based on different
standardization groups were used in the first testing than were used in the
follow-up testing, the overall average difference of about eight IQ points
(evident for all groups) between the two test periods is of no theoretical
importance for the hypothesis of interest. The only important comparisons
are those between the WW, BW, and BB adopted groups within each age level.
They show that:
??The biological offspring have about the same average IQ as has
been reported for children of upper-middle-class parents. Their IQs are
lower, on average than the average IQ of their parents, consistent with the
expected genetic regression toward the population mean (mainly because of
genetic dominance, which is known to affect IQ-see Chapter 7, pp. 189-91).
The above-average environment of these adoptive families probably
counteracts the predicted genetic regression effect to some extent,
expectably more at age seven than at age seventeen.
??The BB adoptees' mean IQ is close to the mean IQ of ninety for
blacks in the same North Central area (from which the BB adoptees came)
reared by their own parents. At age seventeen the BB group's IQ is virtually
identical to the mean IQ of blacks in the North Central part of the United
States. Having been reared from two years of age in a white
upper-middle-class environment has apparently had little or no effect on
their expected IQ, that is, the average IQ of black children reared in the
average black environment. This finding specifically contradicts the
expectation of the cultural-difference explanation of the W-B IQ difference
but is consistent with the default hypothesis.
The BB group is more typical of the U.S. black population than is
the BW group. The BB group's IQ at age seventeen is sixteen points below
that of the whim adoptees and thirteen points below the mean IQ of whites in
the national standardization sample of the WAIS. Thus the BB adoptees' IQ is
not very different frown what would be expected if they were reared in the
average environment of blacks in general (i.e. IQ eighty-five).
The mean IQ of the interracial adoptees (BW), both at ages seven and
seventeen, is nearly intermediate between the WW and BB adoptees, but falls
slightly closer to the WW mean. This is consistent with, but does not prove,
the predicted heterotic effect of outbreeding on IQ. The intermediate IQ at
age seven is (WW + BB)/2 = (117.6 + 95.4)/2 = 106..5, or three points below
the observed IQ of the BW group; at age seventeen the intermediate IQ is
97.5, or one point below the observed IQ of the BW group. Of course, mean
deviations of this magnitude, given the sample sizes in this study, are not
significant. Hence no conclusion can be drawn from these data regarding the
predicted heterotic effect.
But all of the group IQ means do differ significantly from one
another, both at age seven and at age seventeen, and the fact that the BW
adoptees are so nearly intermediate between the WW and BB groups is hard to
explain in purely environmental or cultural terms. But it is fully
consistent with the genetic prediction. An ad hoc explanation would have to
argue for the existence of some cultural effects that quantitatively
simulate the prediction of the default hypothesis, which is derived by
simple arithmetic from accepted genetic theory.
Results similar to those for IQ were also found for scholastic
achievement measured at age seventeen, except that the groups differed
slightly less on the scholastic achievement measures than on IQ. This is
probably because the level of scholastic achievement is generally more
susceptible to family influences than is the IQ. The mean scores based on
the average of five measures of scholastic achievement and aptitude
expressed on the same scale as the IQ (with l.t = 100, G = 15) were:
Nonadopted biological offspring = 107.2, WW adoptees = 103. I, BW adoptees =
100. I, BB adoptees = 95.1. Again, the BW group's mean is but one point
above the midpoint between the means of the WW and BB groups.
In light of what has been learned from many other adoption studies,
the results of this transracial adoption study are hardly surprising. As was
noted in Chapter 7 (pp. 177-79) adoption studies have shown that the
between-family (or shared) environment is the smallest component of
true-score IQ variance by late adolescence.
It is instructive to consider another adoption study by Starr and
Weinberg,p57I based on nearly 200 white children who, in their first year of
life, were adopted into 104 white families. Although the adoptive families
ranged rather widely in socioeconomic status, by the time the adoptees were
adolescents there were nonsignificant and near-zero correlations between the
adoptees IQs and the characteristics of their adoptive families, such as the
parents' education, IQ, occupation, and income. Starr and Weinberg concluded
that, within the range of "humane environments," variations in family
socioeconomic characteristics and in child-rearing practices have little or
no effect on IQ measured in adolescence. Most "humane environments," they
claimed, are functionally equivalent For the child's mental development.
In the transracial adoption study, therefore, one would not expect
that the large differences between the mean IQs of the WW, BW, and BB
adoptees would have been mainly caused by differences in the unquestionably
humane and well-above-average adoptive family environments in which these
children grew up. Viewed in the context of adoption studies in which race is
not a factor, the group differences observed in the transracial adoption
study would be attributed to genetic factors.
There is simply no good evidence that social environmental factors
have a large effect on IQ, particularly in adolescence and beyond, except in
cases of extreme environmental deprivation. In the Texas Adoption Study, for
example, adoptees whose biological mothers had IQs of ninety-five or below
were compared with adoptees whose biological mothers had IQs of 120 or
above. Although these children were given up by their mothers in infancy and
all were adopted into good homes, the two groups differed by 15.7 IQ points
at age 7 years and by 19 IQ points at age 17. These mean differences, which
are about one-half of the mean difference between the low-IQ and high-IQ
biological mothers of these children, are close to what one would predict
from a simple genetic model according to which the standardized regression
of offspring on biological parents is .50.
In still another study, Turkheimeris used a quite clever adoption
design in which each of the adoptee probands was compared against two non
adopted children, one who was reared in the same social class as the adopted
proband's Biological mother, the other who was reared in the same social
class as the proband's adoptive mother. (In all cases, the proband's
biological mother was of lower SES than the adoptive mother.) This design
would answer the question of whether a child born to a mother of lower SES
background and adopted into a family of higher SES background would have an
IQ that is closer to children who were born and reared in a lower SES
background than to children born and reared in a higher SES background. The
result: the proband adoptees' mean IQ was nearly the same as the mean IQ of
the nonadopted children of mothers of lower SES background but differed
significantly (by more than 0.50) from the mean IQ of the nonadopted
children of mothers of higher SES background. In other words, the adopted
probands, although reared by adoptive mothers of higher SES than that of the
probands' biological mothers, turned out about the same with respect to IQ
as if they had been reared by their biological mothers, who were of lower
SES. Again, it appears that the family social environment has a surprisingly
weak influence on IQ. This broad factor therefore would seem to carry little
explanatory weight for the IQ differences between the WW, BW, and BB groups
in the transracial adoption study.
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