AN UNASSAILABLE DEFENSE OF G BUT A SIREN-SONG FOR THEORIES OF INTELLIGENCE
Book Review of Jensen on Intelligence-g-Factor
Mike Anderson
The University of Western Australia
Nedlands
WA 6019
mike@psy.uwa.edu.au
www.uwa.edu.au/user/mike/mike.html
ABSTRACT: Jensen presents a compelling case for the reality of g.
This represents a major scientific achievement. However, I consider
that there are two serious mistakes in his choice of scientific
strategy. The first is to adopt an operational stance -- that is,
to drop all reference to the word 'intelligence' and define our
object of scientific interest as the g-factor. This is a mistake
because the operational stance does not work in science and in this
particular case it strips the g factor of all of its psychological
significance. The second mistake is in his pursuit of the g-nexus,
where biological and psychological variables are related to social
outcomes via g. Without a serious theory of mental structure, this
attempt rings hollow. Indeed such a strategy impedes the more
crucial scientific step of developing a theory of intelligence
which, in the final analysis, is a theory of mental structure.
1. The major impression to take from Jensen's (1998, 1999) "The g
Factor" is that it represents a work of monumental scholarship. I have
nothing but admiration for the way that Jensen has stuck to his task
over the last 20-30 years in establishing the psychological reality of
Spearman's g. In particular, he has developed, and in my view
established, the notion that g might best be thought of as grounded in
differences in speed of information processing. In many ways he has
established this singlehandedly and doggedly with only sporadic,
although valuable, help from others. It is not without regret, then,
that in all probability my review will appear negative. This is only
because my particular area of expertise is in psychological theories of
intelligence, and here I am afraid the book has a hollow centre. This
is not due to any lack in Jensen's scholarship -- as I have said this
is clearly of the highest order. Rather it is a direct consequence of
the scientific road Jensen has chosen. This road involves two
important choices. The first is the operational stance and the second
is reductionism, or more appropriately, consilience (Wilson, 1998).
I. THE OPERATIONAL STANCE
2. For Jensen, the term 'intelligence' has become scientifically
useless because it means too many different things to too many
different people (Jensen, 1999, pp.45-49). Hence, Jensen argues, we
should drop the term and focus on the empirically sure core of
intelligence, namely, the g-factor. Jensen attempts to distance himself
from the much derided definition of intelligence as what the tests
measure, by focusing not on IQ per se but on the undeniable empirical
fact that 'cognitive abilities' covary. Providing independent evidence
for the reality of g and developing a specific hypothesis (that speed
of processing underlies g) form much of the early part of the book.
Undoubtedly this serves to justify the claim that the g factor is a
true discovery and not some necessary artifact of intelligence test
construction. However, for me, much of the good work is undone by
asking us to eschew the wider notion of intelligence and by
operationalising intelligence as the g-factor. It is one thing to
encourage explanations of the empirical regularity that g represents
and quite another to claim that such an explanation is tantamount to a
theory of intelligence. There appears little virtue (scientific or
otherwise) in substituting the 'covariation of abilities' for 'what the
tests test' as a working definition of intelligence. No other serious
science relies on operational definitions (Layzer, 1976), and there is
no clear argument as to why psychology should be any different.
3. Even within the confines of this book we can see the muddles that
operational definitions lead to. On pp.52-53 the distinction between a
'mental ability' and a 'physical ability' is given an operational
definition -- "The ability in question is not a mental ability if its
largest factor loading (in a factor analysis of a wide variety of
abilities) is found on a group factor defined as physical." Yet what
defines mental and physical, other than an implicit theory? And
explicit theories are always to be preferred in science. On this
operational definition it is not possible to have a mental ability that
is more correlated with a 'physical factor' than it is with the
g-factor. This rules out the possibility of a mental function (this
time defined theoretically) that could be related to physical
parameters of the brain, for example, some aspect of linguistic ability
being considered a mental ability. And if this is the case then much
that is interesting about g for psychology (e.g., why are some mental
functions related to g while others are not?) disappears. What Jensen
has established is that any theory of intelligence must take general
intelligence seriously. But the problem of what such a theory should
look like is sidestepped by restricting scientific enquiry to 'general
intelligence' -- he has thrown out the baby with the bathwater.
4. With an operational stance there is always the danger of an infinite
regress and charges of tautology. This is especially so under the
circumstances (as here) where the operational definition (the g-factor
is intelligence) is set up after the empirical conditions that are
supposed to constitute the crucial test of the construct (cognitive
abilities covary) have been established. Empirical regularities provide
the impetus for theories but cannot themselves provide the meaning of
the constructs. Rather than providing the sure footing for scientific
study, the operational stance has been the Achilles heel of Jensen's
work. It has allowed the claim that g is a tautological consequence of
test construction to survive much longer than it ought to have done.
But in my view there is a more serious and potentially fatal mistake in
Jensen's choice of scientific strategy.
II. THE CONSILIENCE STRATEGY
5. Having established that g is 'real' (i.e., it is not an artifact of
test construction, power elites or factor analysis), and that a good
working hypothesis is that g may be based on differences in speed of
information processing (as measured by reaction times, inspection times
and maybe even some brain-based measures), where does Jensen then lead
us? First, he moves 'down' to argue that it is this same g that is the
core of the heritability of IQ. Second, he moves 'up' to show how a
'theory of g' might make sense of race differences in IQ. In so doing,
he bridges genetics, g, and race differences in one superstructure,
thereby establishing what he comes to call the g-nexus. The g-nexus
represents the variables that are linked through g -- "education,
employment, income, poverty, crime and other social pathologies"
(p.555) on the one hand, and IQ, speed of processing, brain physiology
and genetics on the other. Herein lies the mistake. The attempt to link
biological and psychological variables with social outcomes via g is a
mistake, not because such a framework is considered by some as
unsavoury (I, for one, don't particularly care whether or not race
differences are based on genetic differences), but because, I believe,
it is the wrong scientific strategy.
6. The strategy he has chosen might be called reductionism because his
first step is to attempt to establish that it is g that is the basis of
the heritability of IQ. In other words g is reduced to genes. The
strategy can also be considered reductionistic because the social
phenomena are to be explained, substantially, by differences in g which
are in turn to be explained by differences in genes. However, given
that the g factor itself sits in the middle of this causal chain, I
prefer the term consilience (Wilson, 1998). Consilience is the search
for the unity of knowledge involving, in theory at least, the linking
of many different levels of explanation from quantum mechanics to
social behaviour in an integrated causal chain. Wilson argues that
consilience is the ultimate goal of science. I think the consilience
strategy has been the wrong choice for the science of intelligence --
mainly because for consilience to work we need an adequate theory at
the psychological level, and we are a long way from having that.
Jensen's contribution is to establish the g-factor at the core of
theories of intelligence. However, both his operational stance (i.e.,
the g-factor is intelligence) and his search for consilience have taken
him away from developing the theory itself. In my view this has led to
a number of unfortunate consequences:
(i) Scientists in the field, taking the lead from Jensen, have
concentrated too much on searching for physiological correlates of
IQ. In my view much of this effort will be wasted in the absence
of a proper theory of mental structure with which to interpret
these data.
(ii) Even more problematic has been the encouragement of work that
explores the g-nexus. While it is an interesting hypothesis for
sociology and education that 'general intelligence' may mediate
biology and social phenomena, the hypothesis is not particularly
psychological. With no flesh on its bones, that is to say yet
again with no theory of mental structure, it can only ever be
correlational in the same way that the relationship between say
unemployment rates and mental illness is only of marginal
psychological interest.
(iii) The consilience strategy takes us into the murky and
dangerous worlds of race and genes, and this has turned away a
generation of potential researchers into the psychology of
intelligence. Frankly, the g factor appears psychologically barren
and not worth the heat it has generated. The g-nexus is important,
I think, if you work in sociology or education. However, to attempt
nothing more than the identification of variables that might
explain group differences in social outcome is just scientifically
uninteresting for theories of mental structure. There is no more
reason to investigate the association between groups divided on
race than there is to investigate groups that differ in height.
Either analysis is uninformative for a theory of mental structure
and ultimately that is what a theory of intelligence should be.
7. The consilience strategy has taken priority over establishing or
formulating a psychological theory of 'intelligence'. While having some
sympathy with Jensen's exasperation with the foot-loose and fancy-free
way that the word intelligence is bandied about, the point is that for
psychology it is intelligence (and not the g factor) that is ultimately
interesting. Surely the next step after establishing the reality of g
(and I must stress that it is not a step we could reasonably expect
Jensen himself to take -- there is only so much that can be done in a
scientific lifetime) should be to show how it fits into a wider
intellectual architecture or structure. In my view, it is not much of a
psychological theory to point out that g is at the apex of a hierarchy
of psychometrically defined abilities (Vernon pretty much said so 50
years ago, anyway). Examples of psychological questions are: What is
the nature of non-g mental abilities? What is the mechanism through
which speed of processing generates a g-factor? How do mechanisms
related to g and more specific abilities change during cognitive
development? Why do differences in speed of processing influence some
mental processes and not others? How can a savant with low IQ master
complex cognitive feats? There is none of this in Jensen's book.
Indeed, such questions have been dismissed with a wave of the hand as
early as pages 128-133 as part of the strategy of advocating the
dreaded operational stance. And yet in my view such questions are at
the core of a psychological theory of intelligence. Understanding
mental architecture is the linch-pin for understanding many things that
a science of intelligence should be able to inform.
8. At this point I do have to declare an interest. After acknowledging
the reality of g, and owing mainly to Jensen's own work, I have adopted
the opposite scientific strategy, and attempted to build a theory of
intelligence that addresses psychological issues but has the g factor
at its core (Anderson, 1986, 1992). I would have dearly loved to have
someone of Jensen's formidable intellectual talent and work ethic
challenge my theoretical conception of intelligence. Instead, I find
that most people working in intelligence research are largely
uninterested in theoretical development, and prefer to pursue the
consilience strategy (with some notable exceptions, for example,
Detterman, 1987, Nettelbeck, 1999). Inevitably this will sound like
sour grapes on my part, but if it does I will have to endure that
embarrassment. For it is not the absence of any reference to my theory
per se but the absence of any concern to engage in a discussion about
psychological theory that I find disappointing and ultimately
disturbing.
9. The consequences of ignoring the development of theory are
profound. Jensen pursues the strategy of reporting yet more
correlations that are consistent with the 'g-is-speed' hypothesis.
Often this involves crossing measurement, descriptive and explanatory
levels in a haphazard and opportunistic fashion -- for example,
correlating intelligence tests, school performance, reaction times,
inspection times, evoked potentials and nerve conduction rates. Much of
these data I find unconvincing because it is not clear what speed of
processing means and consequently whether all these different
techniques are measuring it (ironically, this lack of specificity
reminds me of Gardner's strategy to establish the validity of multiple
intelligences). But in the absence of a theory, where are all these
data supposed to lead us beyond the already established conclusion that
g is real and biological in origin?
10. It seems to me that 'The g-Factor' is best regarded as the rampart
that others who would deny the reality of general intelligence as a
biological constraint on cognitive abilities must assail. And as such I
can imagine no more daunting stronghold. However, as a strategy for the
scientific understanding of human intelligence it threatens to lead us
into a wilderness from which there will be no return.
REFERENCES
Anderson, M. (1992). Intelligence and development: A cognitive theory.
Oxford: Blackwell.
Anderson, M. (1986). Understanding the cognitive deficit in mental
retardation. Journal of Child Psychology and Psychiatry, 27, 297-306.
Detterman, D.K. (1987). Theoretical notions of intelligence and mental
retardation. American Journal of Mental Deficiency, 92, 2-11.
Jensen, A.R. (1998). The g factor: The science of mental ability.
Westport, CT: Praeger.
Jensen, A.R. (1999). Precis of: "The g Factor: The Science of Mental
Ability" PSYCOLOQUY 10(023).
ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1999.volume.10/
psyc.99.10.023.intelligence-g-factor.1.jensen
http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?10.023
Layzer, D. (1976). Science or superstition? A physical scientist looks
at the IQ controversy. In N. Block & G. Dworkin (Eds) The IQ
controversy. New York: Pantheon.
Nettelbeck, T. (1999). Savant syndrome: Rhyme without reason. In M.
Anderson (Ed), The development of intelligence. Hove: Psychology
Press.
Wilson, E.O. (1998). Consilience: The unity of knowledge. London:
Little, Brown & Co.
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