From the issue dated December 13,
2002
http://chronicle.com/weekly/v49/i16/16b01001.htm
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Is Sociobiology Ready for Prime Time?By NORA S.
NEWCOMBE
Steven Pinker's new book, The
Blank Slate: The Modern Denial of Human Nature (Viking)), consists of 509
pages explaining why we must be serious about human nature and extolling the
virtues of the kind of theorizing often called sociobiology. In particular,
sociobiologists think that many aspects of animal and human behavior can be
understood as biologically based tendencies that evolved in order to increase an
individual's chances of passing his or her genes on to subsequent generations.
Pinker notes in his preface the reactions he got from his colleagues when he
announced what his book was going to be about: "Not another book on
nature and nurture! Are there really people out there who still believe that the
mind is a blank slate?" Although his colleagues obviously didn't dissuade Pinker
from finishing the book, I think they have a point.
The pendulum of
popular and scholarly thinking has already swung away from the standard
social-science model that Pinker criticizes, the one that assumed the primacy of
culture. For example, magazines frequently show pictures of brains studied while
their owners work at various tasks, along with text implying that biology
determines the differences among people in the levels of activity in various
areas of the brain. Sociobiology seems, in fact, already to constitute the new
standard paradigm.
Given that predominance, two questions must be asked
about the enterprise. First, is sociobiology up to the task of being a paradigm
for productive scientific research, or do its explanations for human behavior
lack the bread-and-butter proof that empirical scientists seek to provide?
Second, does sociobiologists' fascination with biological causes lead them to
ignore the possibilities of plasticity and change in human
behavior?
Let's take a look at one research area to illustrate those
issues. Sex differences in spatial ability are frequently the source of
cocktail-party conversation and entertaining cartoons. We are all familiar with
the stereotypes of the man who forges intrepidly into the wilderness armed only
with an innate sense of direction, and the woman who holds maps upside down and
depends on the kindness of strangers.
Nor are those images entirely
false. Studies using standardized tests support the belief that men are markedly
better than women at some spatial tasks. For example, the ability of the average
male to mentally rotate the image of a three-dimensional object exceeds the
ability of the average female by at least one standard deviation. For the
statistically uninitiated, that large a difference is likely to be obvious to
the casual observer; it is a difference one hardly needs science to reveal. Why
are men and women so different? Are the differences set in
stone?
Sociobiologists have a ready explanation for the sexes' different
spatial abilities. Actually, they have two explanations. Both focus on the
reproductive advantage that men with good spatial ability might have over other
men, an advantage that would not apply to women.
One explanation focuses
on Man the Hunter. Men are generally the hunters in hunting-gathering societies,
and spatial skill is important in several components of hunting, including
making weapons, tracking animals, and aiming the weapons at them. The protein
that a man can get from hunting and give to his children helps ensure their
survival, and prowess in hunting may also enhance a man's access to women (who
wish to have a skilled hunter to provide for their children). In addition, a
man's ability to aim may come in handy in any struggles for dominance with other
males over sexual access to females.
The second explanation focuses on
the Man Who Gets Around. Men need spatial skill to navigate around the territory
so as to find as many fertile women as possible. There is in fact beautiful
observational and experimental evidence of that kind of effect in the vole, a
small mammal. One species, the prairie vole, forms pair bonds. A very similar
species, the meadow vole, has a mating system in which females occupy
territories; during the mating season, males make the rounds of females,
attempting to reach as many as possible in time to impregnate them.
Strikingly, spatial ability (assessed by the ability to navigate mazes)
is equal for males and females in the pair-bonded prairie vole, but male meadow
voles beat females at spatial tasks during the mating season, when the part of
their brain that supports navigation (the hippocampus) actually enlarges to meet
the reproductive challenge.
Both Man the Hunter and the Man Who Gets
Around seem sensible explanations of a sex difference in spatial ability. But
rather than be dazzled by their surface plausibility, shouldn't we take a close
look at their assumptions, and see to what extent the links in their arguments
are supported (or undermined) by empirical proof? When we do that, we see that
neither explanation is convincing.
Looking first at Man the Hunter, we
note that although he may need spatial skill, so does Woman the Gatherer.
Gathering may require long trips away from home to find various kinds of edible
plants in their ripening seasons. True, animals move while vegetation sits
still, but much hunting by our ancestors -- far from the swiftest creatures
around -- may have consisted of setting traps, waiting at water holes, and
other stationary activities, rather than tracking animals over meandering paths.
In terms of manufacturing artifacts to use in hunting and gathering, spatial
skill is just as necessary in weaving baskets or making pottery as it is in
fashioning arrows and spearheads. Lastly, while the aiming component of hunting
is a kind of action in space, it does not appear to be a spatial skill. Studies
of aiming have found no correlation between success in hitting a target and
success in rotating an image mentally.
Now take a look at the Man Who
Gets Around. That explanation ignores one important fact: Women, unlike female
meadow voles, live in social groups rather than occupying widely separated home
territories. The skill it takes to impregnate many females probably relies more
on abilities like charm and stealth than on the ability to find one's way among
a cluster of huts.
The sociobiological explanations of sex differences in
spatial ability raise another question, one that is inspired by sociobiology
itself. What is the evolutionary advantage in a difference between the sexes in
a trait that could benefit both sexes, when the trait carries no obvious
metabolic cost? Most sex-specific traits that enhance reproduction produce
antlers or ornamental tails, objects that are cumbersome and costly for the body
to produce, and that a male has only because they enhance his ability to do
combat with other males or to attract females. There is no reason for both sexes
not to have a cheap-to-produce trait that is useful in a wide variety of
settings.
So why is there a sex difference in spatial ability? One clue
comes from a set of observations that sociobiologists often take to support
their explanations -- namely, data that indicate (although sometimes
inconsistently) that spatial ability within each sex fluctuates with hormone
levels. Women often show better spatial skills when they are menstruating. Men
with relatively low testosterone levels often have better spatial skills than
other men.
But although correlations with hormone levels support some
kind of biological explanation, they don't fit in the sociobiological
explanations. There is no obvious reproductive advantage for women to have
enhanced spatial skill at the infertile part of their cycle, and no obvious
reason why spatial skill should vary at all with testosterone level for men
-- or why the relationship is inverse rather than direct, as is the case
for other behavioral traits like aggression. (One could argue that if a man
can't compete physically with other men for mates, he needs spatial ability to
find women, but once again that ignores the key fact about humans' living in
social groups.)
Sex differences in spatial ability may exist because they
are only accidentally linked to hormone levels -- they are a "spandrel," to
use Stephen Jay Gould's term. After all, hormones account both for the
appearance of acne at adolescence and for the fact that acne is typically more
severe for males than females, but no one would suggest that acne confers a
reproductive advantage. Acne is an example of a trait with a sex difference that
is almost certainly accidental, and spatial ability may well be
another.
Now let's turn to the second worry I raised about sociobiology
-- that fascination with biological explanations may divert public
attention from the possibility of malleability. The role of nature in setting
parameters for human behavior does not exclude a substantial role for the
environment in determining what behaviors are exhibited and what differences in
behavior are observed.
Spatial ability again provides an example. Even
though sex differences in the trait are substantial, levels of spatial ability
do not seem to be biologically fixed. Spatial ability increases with schooling
and with training and practice on specific tasks. Like other intellectual
abilities, spatial ability has increased in the past century faster than any
gene could change; that general increase has been called the Flynn effect after
its discoverer, the political scientist James R. Flynn.
If we want to
maximize the human capital available for occupations that draw on spatial skill,
like mathematics, engineering, architecture, physics, chemistry, geology, and
computer science, we would do better to concentrate on learning how to improve
people's spatial abilities, rather than trying to understand the sex
difference.
My point is not that sociobiology is wrong or evil, nor that
we should return to the standard social-science paradigm. Rather, now that we
have accepted that human nature is not a blank slate, we should carefully
investigate what is written on it using our accepted standards of evidence,
proof, and logic. We can expect that, as is true in all of science, some
sociobiological explanations will be upheld (some already have been), while
others will be found wanting. What we all want to read, eventually, is the book
entitled What's Inscribed on the Human Slate, and What We Can and Cannot Do
About It.
Nora S. Newcombe is a professor of psychology at Temple
University. Her most recent book is Making Space: The Development of Spatial
Representation and Reasoning (MIT Press, 2000), written with Janellen
Huttenlocher.
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Section: The Chronicle
Review
Volume 49, Issue 16, Page B10
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Copyright ©
2002 by The Chronicle of Higher Education