[Signs: Journal of Women in Culture and Society 2005, vol. 30, no. 2]
䉷2005 by The University of Chicago. All rights reserved. 0097-9740/2005/3002-0006$10.00
The Bare Bones of Sex: Part 1—Sex and Gender
Here are some curious facts about bones. They can tell us about the
kinds of physical labor an individual has performed over a lifetime
and about sustained physical trauma. They get thinner or thicker (on
average in a population) in different historical periods and in response to
different colonial regimes (Molleson 1994; Larsen 1998). They can in-
dicate class, race, and sex (or is it gender—wait and see). We can measure
their mineral density and whether on average someone is likely to fracture
a limb but not whether a particular individual with a particular density
will do so. A bone may break more easily even when its mineral density
remains constant (Peacock et al. 2002).
Culture shapes bones. For example, urban ultraorthodox Jewish ado-
lescents have lowered physical activity, less exposure to sunlight, and drink
less milk than their more secular counterparts. They also have greatly
decreased mineral density in the vertebrae of their lower backs, that is,
the lumbar vertebrae (Taha et al. 2001). Chinese women who work daily
in the ﬁelds have increased bone mineral content and density. The degree
of increase correlates with the amount of time spent in physical activity
(Hu et al. 1994); weightlessness in space ﬂight leads to bone loss (Skerry
2000); gymnastics training in young women ages seventeen to twenty-
seven correlates with increased bone density despite bone resorption
caused by total lack of menstruation (Robinson et al. 1995). Consider
also some recent demographic trends: in Europe during the past thirty
years, the number of vertebral fractures has increased three- to fourfold
for women and more than fourfold for men (Mosekilde 2000); in some
Thanks to the members of the Pembroke Seminar on Theories of Embodiment for a
wonderful year of thinking about the process of body making and for their thoughtful
response to an earlier draft of this essay. Credit for the title goes to Greg Downey. Thanks
also to anonymous reviewers from Signs for making me sharpen some of the arguments.
Munro Peacock et al. write: “The pathogenesis of a fragility fracture almost always
involves trauma and is not necessarily associated with reduced bone mass. Thus, fragility
fracture should neither be used synonymously nor interchangeably as a phenotype for os-
teoporosis” (2002, 303).
groups the relative proportions of different parts of the skeleton have
changed in recent generations.
(See also table 1.)
What are we to make of reports that African Americans have greater
peak bone densities than Caucasian Americans (Aloia et al. 1996; Gilsanz
et al. 1998),
although this difference may not hold when one compares
Africans to British Caucasians (Dibba et al. 1999), or that white women
and white men break their hips more often than black women and black
men (Kellie and Brody 1990)?
How do we interpret reports that Cau-
casian men have a lifetime fracture risk of 13–25 percent compared with
Caucasian women’s lifetime risk of 50 percent even though once peak
bone mass is attained men and women lose bone at the same rate (Seeman
1997, 1998; NIH Consensus Statement Online 2000)?
Such curious facts raise perplexing questions. Why have bones become
more breakable in certain populations? What does it mean to say that a
lifestyle behavior such as exercise, diet, drinking, or smoking is a risk factor
for osteoporosis? Why do we screen large numbers of women for bone
density even though this information does not tell us whether an individual
woman will break a bone?
Why was a major public policy statement on
women’s health unable to offer a coherent account of sex (or is it gender?)
differences in bone health over the life cycle (Wizemann and Pardue
2001)? Why, if bone fragility is so often considered to be a sex-related
trait, do so few studies examine the relationships among childbirth, lac-
tation, and bone development (Sowers 1996; Glock, Shanahan, and
Such curious facts and perplexing questions challenge both feminist
and biomedical theory. If “facts” about biology and “facts” about culture
are all in a muddle, perhaps the nature/nurture dualism, a mainstay of
For example, sitting height reﬂects trunk length (vertebral height) vs. standing height,
which reﬂects the length of the leg bones. These can change independently of one another.
Thus height increases can result from changes in long bone length, vertebral height, or both.
See Meredith 1978; Tanner et al. 1982; Malina, Brown, and Zavaleta 1987; Balthazart,
Tlemc¸ani, and Ball 1996; Seeman 1997.
The use of racial terms such as Caucasian and others in this article is fraught. But
for the duration of this article I will use the terms as they appear in the sources I cite,
leaving an analysis of this problematic terminology to future publications, e.g., Fausto-
Since a number of studies show no sex difference in hip fracture incidence between
African American men and women, the “well-known” gender difference in bone fragility
may really only be about white women. As so often happens, the word gender excludes
women of color (Farmer et al. 1984).
Peacock et al. write, “Key bone phenotypes involved in fracture risk relate not only to
bone mass but also to bone structure, bone loss, and possibly bone turnover” (2002, 306).
S I G N S Winter 2005 ❙1493
feminist theory, is not working as it should. Perhaps, too, parsing medical
problems into biological (or genetic or hormonal) components in op-
position to cultural or lifestyle factors has outlived its usefulness for bio-
medical theory. I propose that already well-developed dynamic systems
theories can provide a better understanding of how social categories act
on bone production. Such a framework, especially if it borrows from a
second analytic trend called “life course analysis of chronic disease epi-
demiology” (Kuh and Ben-Shlomo 1997; Ben-Shlomo and Kuh 2002;
Kuh and Hardy 2002), can improve our approaches to public health policy,
prediction of individual health conditions, and the treatment of individuals
with unhealthy bones.
To see why we should follow new roads, I consider
gender, examining where we—feminist theorists and medical scientists—
have recently been. In the second part of this study (Fausto-Sterling in
preparation) I will engage with current discussions of biology, race, and
medicine to explore claims about racial difference in bone structure and
Sex and gender (again)
For centuries, scholars, physicians, and laypeople in the United States and
Western Europe used biological models to explain the different social,
legal, and political statuses of men and women and people of different
When the feminist second wave burst onto the political arena in
the early 1970s, we made the theoretical claim that sex differs from gender
and that social institutions produce observed social differences between
men and women (Rubin 1975). Feminists assigned biological (especially
reproductive) differences to the word sex and gave to gender all other
“Sex,” however, has become the Achilles’ heel of 1970s feminism. We
relegated it to the domain of biology and medicine, and biologists and
medical scientists have spent the past thirty years expanding it into arenas
we ﬁrmly believed to belong to our ally gender. Hormones, we learn
(once more), cause naturally more assertive men to reach the top in the
workplace (Dabbs and Dabbs 2001). Rape is a behavior that can be
changed only with the greatest difﬁculty because it is wired somehow into
men’s brains (Thornhill and Palmer 2001). The relative size of eggs and
sperm dictate that men are naturally polygamous and women naturally
monogamous. And more. (See Zuk 2002; Travis 2003 for a critique of
I am grateful to Peter Taylor for insisting that I read the work in life-course analysis.
Stepan 1982; Russett 1989; Hubbard 1990; Fausto-Sterling 1992.
Table 1. Culture Changes Bones
Vertebral BMD (gm/cm
) increased in young women
during an eight-month program of running or
weight-training compared with untrained controls.
Snow-Harter et al. 1992
Two years of aerobics and weight training enhances
BMD in young women; gymnastics training im-
proves mechanical competence of skeleton in boys.
Friedlander et al. 1995; Daly et
Intensive tennis playing increases bone mineral content,
BMAD, and thickness of the humerus of the racket
arm; the effect is especially noticeable in players who
began at ages 9–10, and the effect is there for both
males and females. Later-in-life start-up (29 years)
resulted in more marginal effects.
Jones et al. 1977; Haapasalo et
Cross-country skiers who train year-round have site-
speciﬁc increases in BMD (study on females age
Pettersson et al. 2000
In late-adolescent women, weight-bearing activities are
important for determining bone density; high-impact
activities modify bone width due to increased muscle
strength and lean body mass; lean mass, fat mass,
weight, BMI, years of menstruation, and type of
physical activity explained 81.6 percent of bone
Soderman et al. 2000
In Japanese women with a genetic variant that impairs
vitamin D receptor, exercise, vitamin D, and calcium
intake can increase BMD.
Fujita et al. 1999
Long-term exercise improves balance in older osteoar-
thritic adults (fewer falls).
Messier et al. 2000
In a longitudinal study of youth ages 13–27, maintain-
ing at least an average weight was the best predictor
of high BMD in females.
Welton et al. 1994
Premenopausal, but not postmenopausal, women re-
spond to a regime of vertical jumping exercises with
increased BMD in their femurs.
Bassey and Ramsdale 1994;
Bassey et al. 1998
Physical activity and muscle strength independently
predict BMD in total body and in the proximal fe-
mur in young men.
Nordstrom, Nordstrom, and
Amateur sports at ages 11–30 improves bone density
in a site- or stress-speciﬁc fashion (study done on
Nordstrom et al. 1996; Morel
et al. 2001
Prepubertal Asian Canadian boys have lowered femoral
neck BMC and BMD, ingest 41 percent less cal-
cium, and are 15 percent less active than Caucasian
McKay et al. 2000
S I G N S Winter 2005 ❙1495
Table 1. (Continued)
Over three years, men and women over age 65 receiv-
ing calcium and vitamin D supplements show less
bone loss in the femur and spine and a lower inci-
dence of nonvertebral fractures.
Dawson-Hughes et al. 1997
Ninety percent of adolescent girls and 50 percent of
adolescent boys consume less than optimal amounts
of dietary calcium.
Fifty percent of 12- to 21-year-olds exercise vigorously
and regularly; 25 percent report no vigorous physical
Alcohol consumption correlates with higher BMD,
smoking with lower BMD.
Siris et al. 2001
Anorexia nervosa injures bone development and
Mun˜oz and Argente 2002
In the twentieth century, American youth of African,
European, and Japanese ancestry increased in height
due to changes in sitting height and increase in
lower limb length.
Note: BMD pbone mineral density, BMAD pbone mineral apparent density (the measure
is independent of size), BMI pbody mass index, and BMC pbone mineral content.
these claims.) Feminist scholars have two choices in response to this
spreading oil spill of sex. Either we can contest each claim, one at a time,
doing what Susan Oyama calls “hauling the theoretical body back and
forth across the sex/gender border” (2000a, 190), or, as I choose to do
here, we can reconsider the 1970s theoretical account of sex and gender.
In thinking about both gender and race, feminists must accept the
body as simultaneously composed of genes, hormones, cells, and organs—
all of which inﬂuence health and behavior—and of culture and history
(Verbrugge 1997). As a biologist, I focus on what it might mean to claim
that our bodies physically imbibe culture. How does experience shape the
very bones that support us?
Can we ﬁnd a way to talk about the body
without ceding it to those who would ﬁx it as a naturally determined
object existing outside of politics, culture, and social change? This is a
project already well under way, not only in feminist theoretical circles but
in epidemiology, medical sociology, and anthropology as well.
I use the term experience rather than the term environment here to refer to functional
activity. For more detail see Gottlieb, Whalen, and Lickliter 1998.
Embodiment merges biology and culture
During the 1990s, feminist reconsideration of the sex/gender problem
moved into full swing.
Early in the decade Judith Butler argued com-
pellingly for the importance of reclaiming the term sex for feminist in-
quiry but did not delve into the nuts and bolts of how sex and gender
materialize in the body. Philosopher Elizabeth Grosz (1994) claimed
that sex is neither ﬁxed nor given. In drawing on philosophers such as
Maurice Merleau-Ponty (1962) and Alfred North Whitehead (
1978), Grosz differentiates herself from Butler, holding that materiality
is “primordial, not merely the effect of power” (Alcoff 2000, 858).
Primordial materiality, however, does not mean that purely biological
accounts of human development—no matter how intricate their stories
of cellular function—can explain the emergence of lived and differently
Psychologist Elizabeth Wilson offers one of the most interesting and
far-reaching critiques of feminist attempts to reclaim the body (Martin
1997; Wilson 1998, 1999). Reaching back to Sigmund Freud’s work
on hysteria, Wilson emerges with a new purchase on biology itself. Re-
iterating the varied symptoms produced by psychic trauma (blindness,
localized pain, loss of smell, paralysis), she focuses on the “bio-logic”
of these physical manifestations (1999). “The neurology, physiology, or
biochemistry of hysterical symptomology,” she writes, “can be disre-
garded only in a theoretical milieu that takes certain modes of materiality
to be inert” (1999, 10). She suggests that just as “culture,” “signiﬁ-
cation,” or “sociality” contribute to the production of complex bodily
responses, “biology itself” ought to be investigated as a “site of . . .
complex ontological accomplishment” (10). Such investigation, Wilson
argues, opens the door for a fundamental reexamination of biomedical
analyses of sex differences in physiology and disease patterns. The idea
of embodiment as a dynamic system of biocultural formation reaches
beyond discussions of gender (e.g., Csordas 1990; Ingold 1998; Wil-
liams and Bendelow 1998).
Efforts to reincorporate the body into social theory also come from
the ﬁeld of disability studies. Here too an emphasis on the social con-
Butler 1990, 1993; Gatens 1996; Kirby 1997; Birke 1999.
The “rediscovery” of phenomenology and its application to gendered body image
remains a fruitful arena of feminist body theory, e.g., Weiss 1999.
Although Thomas J. Csordas (1999) suggests that cultural phenomenological analyses
transform understandings of both biology and culture, he is more concerned with how the
body changes culture than vice versa. For a different anthropological point of view, see
S I G N S Winter 2005 ❙1497
struction of disability has been enormously productive. Yet several authors
have broached the limitations of an exclusively constructivist approach.
At least two different types of critique parallel and foreshadow possible
feminist approaches to a reconsideration of the body. The ﬁrst demands
that we recognize the material constraints on the disabled body in its
variable forms and that we integrate that recognition into theory (Williams
and Busby 2000). The second, more radical move is to suggest that “the
disabled body changes the process of representation itself” (Siebers 2001,
738). This latter approach offers a rich resource for feminist theories of
representation and another possible entry point into the analysis of ma-
teriality in actual, lived-in bodies (see also Schriempf 2001).
Sex and gender in the world of biology and medicine
In contrast to these new feminist explorations of the body, in the ﬁeld of
medicine a more limited view of sex differences prevails. Consider a recent
report on sex differences issued by the National Institute of Medicine
and, more broadly, the professional movement called “gender-based med-
icine” promoted by the Society for Women’s Health Research (SWHR).
The SWHR describes itself as “the nation’s only not-for-proﬁt organi-
zation whose sole mission is to improve the health of women through
research. . . . The Society . . . encourages the study of sex differences
that may affect the prevention, diagnosis and treatment of disease and
promotes the inclusion of women in medical research studies” (Schachter
The society lobbies Congress, sponsors research conferences,
and publishes a peer-reviewed academic journal, the Journal of Women’s
Health and Gender-Based Medicine.
A traditional biomedical model of health and disease provides the in-
tellectual framework for the research conferences (Krieger and Zierler
1995). Although much of the research publicized through such confer-
ences seems strictly to deal with sex in the 1970s feminist meaning of the
word, sex sometimes strays into arenas that traditional feminists claim for
gender. Consider a presentation that was said to provide evidence that
prenatal testosterone exposure affects which toys little girls and boys prefer
Since the society receives both foundation and pharmaceutical company funding, its
claim to independence requires scrutiny. The Sex and Gene Expression conferences were
funded by Aventis Pharmaceuticals as well as private foundations. Industry and mainstream
medical care sponsorship does not unethically direct work, but it limits the permissible
ontological and epistemological approaches to the study of women’s health and sex
to play with (Berenbaum 2001). Working within a 1970s deﬁnition of
the sex/gender dualism, the author of this study logically extends the
term sex into the realm of human behavior.
For those familiar with contemporary feminist theory, it might seem
that the large number of biological psychologists who follow similar re-
search programs and the biomedical researchers interested in tracking
down all of the medically interesting differences between men and women
live in a time warp. But members of the feminist medical establishment,
that is, those researchers and physicians for whom the activities and pro-
grams of the SWHR make eminent sense, see themselves perched on the
forward edge of a nascent movement to bring gender equity to the health-
care system. These feminists work outside of an intellectual milieu that
would permit the more revolutionary task proposed by Grosz and Wilson,
among others, that of contesting not only “the domination of the body
by biological terms but also [contesting] the terms of biology itself”
(Grosz 1994, 20).
Within medicine there is a lot of confusion about the terms sex and
gender. Many medical texts use the terms interchangeably, while some
scientists apply the term gender to the study of nonhuman animals, a
problem also debated in the primary biological literature (Pearson 1996;
Thomas et al. 2000). Lack of consistent usage promotes confusion among
scientists, policy makers, and the general public, in effect foreclosing any
space for the analysis of social causes of differences in health outcomes
between men and women (Krieger 2003).
Helen Keane and Marsha Rosengarten (2002) have explored the body
as a dynamic process out of which gender emerges. In a ﬁrst example
they examine the signiﬁcance of anabolic steroid use on the alteration
of sexed bodies, concluding that “the hormonal body is always in process
rather than ﬁxed” (269); they further explore the notion of sex/gender
ﬁxity through a discussion of organ transplantation between XX and XY
individuals. Finally, they examine “the biological as a ﬁeld of transfor-
mations, as active, ‘literate matter’ as well as an effect of mediation and
intervention” (275). I have chosen bone development—an area often
accepted as an irrefutable site of sex difference—to examine Keane and
Rosengarten’s formulation. First, to what extent can we understand bone
formation as an effect of culture rather than a passive unfolding of bi-
ology? Second, can we use dynamic (developmental) systems to ask bet-
ter research questions and to formulate better public-health responses
to bone disease?
S I G N S Winter 2005 ❙1499
Bones are eloquent. Archaeologists read old bone texts to ﬁnd out how
prehistoric peoples lived and worked. A hyperﬂexed and damaged big toe,
a bony growth on the femur, the knee, or the vertebrae, for example, tell
bioarchaeologist Theya Molleson that women in a Near Eastern agricul-
tural community routinely ground grain on all fours, grasping a stone
grinder with their hands and pushing back and forth on a saddle-shaped
stone. The bones of these neolithic people bear evidence of a gendered
division of labor, culture, and biology intertwined (Molleson 1994).
Given that modern forensic pathologists also use bones to learn about
how people live and die, it seems odd that a report from the National
Institute of Medicine, presented as a state-of-the-art account of gender
and medicine, deals only superﬁcially with the sexual differentiation of
bone disease (Wizeman and Pardue 2001).
In a brief three pages on
osteoporosis, the monograph cites dramatic statistics on the frequency of
osteoporosis in European and Caucasian American women and the dan-
gers of the condition. The report offers a laundry list of factors believed
to affect bone health. Jumbled together, with no attempt to understand
their interrelationships or their joint, cumulative contributions to bone
development and loss, are hormones, diet, exercise, genetic background,
vitamin D production, and the bone-destroying effects of drugs such as
cortisone, tobacco, and alcohol. In an anemic end-of-chapter recommen-
dation the authors urge researchers to control for all of the above factors
as they design their research studies. Indeed, failure to engage the task
of formulating new approaches to biology prevented them from making
a stronger analysis.
But osteoporosis is a condition that reveals all of the problems of de-
ﬁning sex apart from gender. A close reading of the osteoporosis literature
further reveals the difﬁculties of adding the variable of race to the mix (a
point I will develop in a forthcoming paper [Fausto-Sterling in prepara-
tion]) while also exemplifying the claim that disease states are socially
produced, both by rhetoric and measurement (e.g., Petersen 1998) and
Perhaps because the ﬁeld of archaeology is still struggling to bring gender into the
fold, its practitioners often insist on the centrality of the sex/gender distinction. Yet their
own conclusions undermine this dualism, precisely because they use a biological product,
bone, to draw conclusions about culture and behavior (Ehrenberg 1989; Gero and Conkey
1991; Wright 1996; Armelagos 1998).
The validity of using bones to identify race is contested (Goodman 1997).
by the manner in which cultural practice shapes the very bones in our
bodies (Krieger and Zierler 1995).
Of bones and (wo)men
The accuracy of the claim that osteoporosis occurs four times more fre-
quently in women than in men (Glock, Shanahan, and McGowan 2000)
depends on how we deﬁne osteoporosis, in which human populations
(and historical periods) we gather statistics, and what portions of the life
cycle we compare. The NIH (2000) deﬁnes osteoporosis as a skeletal
disorder in which weakened bones increase the risk of fracture. When
osteoporosis ﬁrst wandered onto the medical radar screen, the only signal
that a person suffered from it was a bone fracture. Post hoc, a doctor
could examine a person with a fracture either using a biopsy to look at
the structural competence of the bone or by assessing bone density.
If one looks at lifetime risks for fracture, contemporary Caucasian men
range from 13 to 25 percent (Bilezikian, Kurkland, and Rosen 1999)
while Caucasian women (who also live longer) have a 50 percent risk. But
not all fractures result from osteoporosis. One study looked at fracture
incidence in men and women at different ages and found that between
the ages of ﬁve and forty-ﬁve men break more limbs than women.
breaks, however, result from signiﬁcant work- and sports-related trauma
suffered by healthy bones. After the age of ﬁfty, women break their bones
more often than men, although after seventy years of age men do their
best to catch up (Melton 1988).
The most commonly used medical standard for a diagnosis of osteo-
porosis no longer depends on broken bones. With the advent of machines
called densitometers used to measure bone mineral density (of which more
in a moment), the World Health Organization (WHO) developed a new
“operational” deﬁnition: a woman has osteoporosis if her bone mineral
density measures 2.5 times the standard deviation below a peak reference
standard for young (white) women. The densitometer manufacturer usu-
ally provides the reference data to a screening facility (Seeman 1998), and
thus rarely, if ever, do assessments of osteoporosis reﬂect what Margaret
This study (cited in Melton 1988) dates from 1979, and it seems likely that subsequent
cultural changes have led to different patterns of breakage; fracture incidence is a moving
S I G N S Winter 2005 ❙1501
Lock calls “local biologies” (Lock 1998, 39).
With the WHO deﬁnition,
the prevalence of osteoporosis for white women is 18 percent, although
there is not necessarily associated pathology, since now, by deﬁnition, one
can “get” or “have” osteoporosis without ever having a broken bone.
The WHO deﬁnition is controversial, since bone mineral density (BMD,
) accounts for approximately 70 percent of bone strength,
while the other 30 percent derives from the internal structure of bone
and overall bone size. And while women with lower bone density are 2.5
times more likely to experience a hip fracture than women with high bone
densities, high risks of hip fracture emerge even in women with high bone
densities when ﬁve or more other risk factors are present (Cummings et
Furthermore, it is hard to know how to apply the criterion,
based on a baseline of young white women, to men, children, and mem-
bers of other ethnic groups. To make matters worse, there is a lack of
standardization between instruments and sites at which measurements are
Thus it comes as no surprise that “controversy exists among ex-
perts regarding the continued use of this [WHO] diagnostic criterion”
(NIH Consensus Statement Online 2000, 3).
There is a complicated mixture at play. First, osteoporosis—whether
deﬁned as fractures or bone density—is on the rise, even when the in-
creased age of a population is taken into account (Mosekilde 2000). At
the same time, it is hard to assess the danger of osteoporosis, in part due
to drug company–sponsored “public awareness” campaigns. For example,
in preparation for the sales campaign for its new drug, Fosamax, Merck
Pharmaceuticals gave a large osteoporosis education grant to the National
Osteoporosis Foundation to educate older women about the dangers of
osteoporosis (Tanouye 1995).
Merck also directly addressed consumers
Local biologies reﬂect local differences in biology. For example, hot ﬂashes are far less
frequent in Japan than in the United States, possibly for reasons pertaining to diet. The
normalization question here is: Is it best to compare a population to its own group or some
group with similar environmental and genetic histories, or to some outgroup standard?
These factors include: a mother having broken her hip, especially before age eighty;
height at age twenty-ﬁve (taller women are more likely to break hips); extreme thinness;
sedentary lifestyle; poor vision; high pulse rate; the use of certain drugs; etc.
One researcher states: “I think what is also of note, is that the between-center dif-
ferences are greater than between-sex differences within certain centers” (Lips 1997, 95).
Fosamax seems to be able to prevent further bone loss in people who are losing bone
and to build back lost bone at least in the hip and spine. In discussing Merck’s campaign,
I do not argue that the drug is useless (in fact, I am taking it!), merely (!) that drug companies
play an important role in the creation of new “disease” and proﬁt as a result.
with television ads contrasting frail, pain-wracked older women with lively,
attractive seniors, implying the urgent need for older women to use Fos-
amax (Fugh-Berman, Pearson, Allina, Zones, Worcester, and Whatley
Mass marketing a new drug, however, requires more than a public
awareness campaign. There must also be an easy, relatively inexpensive
method of diagnosis. Here the slippage between the new technological
measure—bone density—and the old deﬁnition of actual fractures and
direct assessment of bone structure looms large. Merck promoted afford-
able bone density testing even before it put Fosamax on the market. The
company bought an equipment manufacturing company and ramped up
its production of bone density machines while at the same time helping
consumers ﬁnd screening locations by giving a grant to the National
Osteoporosis Foundation to push a toll-free number that consumers (pre-
sumably alarmed by the Merck TV ads) could call to ﬁnd a bone density
screener in a locale near them (Tanouye 1995; Fugh-Berman, Pearson,
Allina, Zones, Worcester, and Whatley 2002).
The availability of a simple technological measure for osteoporosis also
made scientiﬁc research easier and cheaper. The majority of the thousands
upon thousands of research papers on osteoporosis published in the ten
years from 1995 to 2005 use BMD as a proxy for osteoporosis. This is
true despite a critical scientiﬁc literature that insists that the more expensive
volumetric measure (grams/cm
) more accurately measures bone strength
and that knowledge of internal bone structure (bone histomorphometry)
provides essential information for understanding the actual risk of fracture
The explosion of knowledge about osteoporosis cod-
iﬁes a new disorder, still called osteoporosis but sporting a newly simpliﬁed
account of bone health and disease.
Ego Seeman (1997) laments the
“An association between the change in areal bone density and the change in fracture
rates has never been documented” (Seeman 1997, 517). According to the NIH Consensus
Statement Online: “Currently there is no accurate measure of overall bone strength” (2000,
5). But BMD is often used as a proxy. The National Women’s Health Network cites the
pitfalls of using BMD to predict future fractures (Fugh-Berman, Pearson, Allina, Zones,
Worcester, Whatley, Massion, et al. 2002), but others cite a strong association between BMD
and fracture rate (e.g., Melton et al. 1998; Siris et al. 2001). One overview of studies that
attempted to predict osteoporosis-linked fractures with bone mineral density concluded:
“Measurements of bone mineral density can predict fracture risk but cannot identify indi-
viduals who will have a fracture. We do not recommend a programme of screeningmenopausal
women for osteoporosis by measuring bone density” (Marshall, Johnell, and Wedell 1996,
1254). See also Nelson et al. 2002.
For a history of the concept of osteoporosis, see Klinge 1998.
S I G N S Winter 2005 ❙1503
use of the density measure, which, he argues, “affects the way we con-
ceptualize the skeleton (or fail to), and the way we direct (or misdirect)
our research,” and “blind[s] us to the biology of bone” (510).
Weaving together these threads—increasing lifetime risk, new disease
deﬁnitions, and easier measurement—produces an epistemological trans-
formation in our scientiﬁc accounts of bones and why they break. The
transformation is driven by a combination of cultural forces (why are
fracture rates increasing?) and new technologies generated by drug com-
panies interested in creating new markets, disseminated with the help of
market forces drummed up by the self-same drug companies, and aided
by consumer health movements, including feminist health organizations
such as the Society for Women’s Research, which argue that gender-based
differences in disease have been too long neglected.
Analyzing bone development within the framework of sex versus gender
(nature vs. nurture) makes it difﬁcult to understand bone health in men
as well as women. Those trying to decide on a proper standard to measure
fracture risk in men (should they use a separate male baseline or the only
one available, which is for young, white women?) struggle with this prob-
lem of gender standardization (Melton et al. 1998). There are differences
between men and women, although osteoporosis in men is vastly under-
studied. In a bibliography of 2,449 citations of papers from 1995 to 1999
(Glock, Shanahan, and McGowan 2000), only 47 (2 percent) addressed
osteoporosis in men. But making sense of patterns of bone health for
either or both sexes requires a dynamic systems approach. A basic starting
place is to ask the development question.
For instance, we ﬁnd no difference in bone mineral density in (Cau-
casian) boys and girls under age sixteen but a higher bone mineral density
in males than in females thereafter (Zanchetta et al. 1995). This difference
(combined with others that develop during middle adulthood) becomes
important later in life, since men and women appear to lose bone at the
same rate once they have reached a peak bone mass; those starting the
loss phase of the life cycle with more bone in place will be less likely to
develop highly breakable bones. Researchers offer different explanations
for this divergence. Some note that boys continue to grow for an average
of two years longer than girls (Seeman 1997). The extra growth period
strengthens their bones by adding overall size. Others point additionally
to hormones, diet, physical activity, and body weight as contributing to
the emerging sex (or is it gender?) difference at puberty (Rizzoli and
So differences in bone mineral density between boys and girls emerge
during and after puberty, while for both men and women peak bone mass
and strength is reached at twenty-ﬁve to thirty years of age (Seeman 1999).
Vertebral height is the same in men and women, but vertebral width is
greater in men. The volume of the inner latticework does not differ in
men and women, but the outer layer of bone (periosteum) is thicker in
men. Both width and outer thickness strengthen the bone. In general,
sex/gender bone differences at peak are in size rather than density (Bil-
ezikian, Kurkland, and Rosen 1999).
This life-cycle analysis reveals three major differences in the pattern of
bone growth and loss in men compared with that in women. First, at
peak, men have 20 to 30 percent more bone mass and strength than
women. Second, following peak, men but not women compensate for
bone loss with new increases in vertebral width that continue to strengthen
the vertebrae. Over time both men and women lose 70 to 80 percent of
bone strength (Mosekilde 2000), but the pattern of loss differs. In men
the decline is gradual, barring secondary causes.
In women it is gradual
until perimenopause, accelerates for several years during and after the
menopause, and then resumes a gradual decline.
Lis Moskilde (2000)
points out that the rush to link menopause to osteoporosis has led to the
neglect of two of the three major differences in the pattern of bone growth
between men and women. Yet these two factors are speciﬁcally linked to
physical activity, and thus amenable to change earlier in life.
Indeed, many studies on children and adolescents address the contri-
bution sociocultural components of bone development make to male-
female differences that emerge just after puberty (see table 1). But the
overwhelming focus on menopause as the period of the life cycle in which
women enter the danger zone steers us away from examining how earlier
sociocultural events shape our bones (see Lock 1998). Once menopause
enters the picture, the idea that hormones are at the heart of the problem
overwhelms other modes of thought.
Nor is it clear how hormones affect
A secondary cause might be bone loss due to an eating disorder or a metabolic disease,
or the prolonged use of a bone-leaching drug such as cortisone.
When I use the words men and women I refer to particular populations on which these
studies were done. These are mostly Caucasian and Northern European or North American.
Most of the studies have been done since the 1980s, but bone size, shape, and growth
patterns would have differed at the beginning of the twentieth century compared with their
appearance at the beginning of the twenty-ﬁrst. I will not make these points every time I
use these words.
So powerful is the focus on old age that the long NIH bibliography on menopause
completely ignores the possible importance of pregnancy and lactation on bone development.
These two processes are profoundly implicated in calcium metabolism, and if there is no
effect on later bone strength it would be important to ﬁnd out why. What physiological
S I G N S Winter 2005 ❙1505
bone development and loss. In childhood, growth hormone is essential
for long bone growth, the gonadal steroids are important for the cessation
of bone growth at puberty, and probably both estrogen and testosterone
are important for bone health maintenance (Damien, Price, and Lanyon
1998). The details at the cellular level have yet to be understood (Gas-
Basic bone biology
In the fetus, cartilage creates the scaffolding onto which bone cells climb
before secreting the calcium-containing bone matrix that becomes the
The cells that secrete the bone matrix are called osteoblasts.
As they grow, bones are shaped by the strains and stresses put on them
by the activity of their owner. Osteoblasts deposit matrix at some sites,
while another cell type, the osteoclast, can chip away at areas of too much
growth. Growing bones change shape through this give and take of os-
teoblast and osteoclast activity in a process called bone remodeling.
bones increase in length throughout childhood by adding on new material
at their growing ends. These growth sites close as a result of hormonal
changes during puberty, but bone reshaping continues over the course of
a life (Currey 2002).
Bone contains two important types of tissue, which can be seen (ﬁg.
1, A) if one cuts it across the middle. The outer dense, hard layer is called
compact tissue; the inner layer contains cancellous tissue consisting of a
latticework of slender ﬁbers. The ﬁbers of this interior bone lattice fuse
into longer structures called trabeculae (Latin for “small beam”) that
crisscross the interior of the bone. The periosteum (literally, “around the
bone”), a layer of tissue through which blood vessels and nerves pass into
the interior, covers the bone.
Osteoblasts clinging to the periosteum and around the trabecular struts
of the bone’s interior can produce new bone in both locations. Osteoblasts
can also transform into osteocytes, cells found in large numbers inside the
hard bone tissues (Currey 2002). Osteocytes probably play an important
mechanisms protect the bone of pregnant and lactating women? This is an example of a
biological question that lies fallow because of the focus on supposed estrogen deﬁciency in
The bone matrix is made up primarily of a substance called hydroxyapatite that is
mostly composed of crystalline forms of the molecules calcium phosphate, calciumcarbonate,
and small amounts of magnesium, ﬂuoride, and sulfate.
One memory device for remembering which cell is which is to think that osteoBlasts
Build bone and osteoClasts Chomp on bone.
Figure 1 Vertebral structure. Scanning electron micrographs of longitudinal sections of
human vertebrae. This image is a modiﬁcation of one published in Mosekilde 2000. (A)
Healthy vertebra showing the trabecular structure of the cancellous bone (inset) and the
surrounding periosteum. Note the regular vertical arrangement and density of the trabeculae.
(B) A vertebra exhibiting osteoporosis. Note the increased number and size of spaces where
cross struts have broken, as well as the less organized and less dense trabecular structure.
role in bone regeneration when they produce chemical signals that tell
osteoblasts that the bone is under mechanical strain and needs to grow
(Mosley 2000). Osteoblasts cannot form new bone unless the surface on
which they sit is under a mechanical strain, which explains why exercise
remains such an important component of bone health while weightlessness
in space or prolonged bed rest result in the loss of bone thickness.
Moreover, osteoblasts only add new bone on preexisting surfaces. A person
with osteoporosis develops breaks in the tiny cross beams, and these widen
into holes that riddle the bone’s interior (ﬁg. 1, B). A lost strut cannot
be replaced because there is no old surface on which to lay down a new
mineral layer. A thinning strut, however, can thicken again if the osteoblast
produces more new bone than the osteoclast breaks down (Parﬁtt 1988;
Bone development, then, is profoundly inﬂuenced by what physiolo-
gists call functional adaptation. Although a great deal remains to be under-
stood about the biology of use and disuse, some basic principles are already
evident. First, both disuse and predictable moderate use result in bone
resorption and increased porosity. However, dynamic strain, that is, strain
that is unpredictable and of varied impact level, can lead to a linear increase
in bone mass (Mosley 2000).
Bones may adopt strain thresholds such
Stress can be from direct impact or from tension placed on the bones by attached
muscles. For more details on the importance of mechanical strain on bone development, see
Skerry and Lanyon 1995; Mosekilde 2000; Mosley 2000.
In animal models it is possible to induce new bone formation (modeling) without ﬁrst
having caused bone resorption (Pead, Skerry, and Lanyon 1988).
S I G N S Winter 2005 ❙1507
that only strains above such thresholds induce new bone formation. Strain
thresholds may change over the life cycle. Perhaps the decline in estrogen
associated with menopause resets the threshold to a higher strain level,
thus requiring very high levels of bone stress to stimulate new bone for-
mation. Such dynamic theories allow us to understand how behavior (e.g.,
changing forms of exercise) and hormonal changes in the body might
together produce bone loss or gain (Frost 1986, 1992).
Even such a simpliﬁed account of bone development and maintenance
shows how hard it can be to understand why people in one group break
their bones more often than people in another. Groups may differ in peak
bone size even if bone loss later in life is the same. The trabeculae on the
bone’s inside might be thicker in one group than another, or the outside,
compact bone layer might be thicker. There could be less bone loss or a
reduction in bone turnover (the balance between osteoclast and osteoblast
activity). Trabecular loss could result from thinning rather than perfora-
tion, or there could be more new bone formation in the periosteum or
less resorption in the bone’s interior. What is most striking about the
medical literature on osteoporosis is that “whether these differences in
bone size, mass, or structure, or bone turnover among ethnic groups or
between men and women even partly account for the corresponding group
differences in fracture rates is unknown” (Seeman 1997, 517).
Genes, of course, are involved in all of the events described in the
previous few paragraphs. Rather than as causes of bone construction and
destruction, however, genes are best understood as mediators, suspended
in a network of signals (including their own) that induce them to syn-
thesize new molecules.
The molecules they make may help to produce
more bone or to break down existing bone. Either action may, in turn,
be a direct effect (e.g., making a structural element such as collagen) or
an indirect effect (e.g., causing the death or sustaining the life of bone-
making cells). Researchers have identiﬁed over thirty genes that affect
bone development either positively or negatively in mice (Peacock et al.
2002), and scientists continue to identify genetic variants affecting bone
density in humans (Boyden et al. 2002; Little et al. 2002; Ishida et al.
Finally, how do hormones ﬁt into all of this? Part of the initial logic
of thinking about osteoporosis as a basic biological (sex) difference be-
One review states that mechanical receptors transform signals from deforming bones
into changes in the shape of DNA regions that regulate the activities of genes involved in
bone formation. The authors write that “bending bone ultimately bends genes” (Pavalko et
al. 2003, 104).
tween men and women derives from the observation that bone thinning
increases dramatically around the time of menopause. Most thus assume
that declining estrogen causes bone loss. Since estrogen codes in most
people’s minds as a quintessentially female molecule, it becomes extraor-
dinarily difﬁcult to conceptualize osteoporosis as a disease with many
contributors stretching over the entire life cycle. Here, gender constructs
(Fausto-Sterling 2000) combined with the proﬁts derived from selling
estrogen replacement have contributed mightily to shaping the course of
scientiﬁc research in this ﬁeld. Estrogen, though, is only one of a number
of hormones linked to bone physiology.
At least three major hormone systems acting both independently of
one another and through mutual inﬂuence regulate bone formation and
loss. Fascinatingly, at least two of these operate at times through the brain
and the sympathetic (involuntary) nervous system.
The ﬁrst system in-
cludes three major hormones that maintain proper calcium levels through-
out the body, dipping into the bone calcium reservoir as needed.
hormones (the active form of vitamin D; parathyroid hormone [PTH],
which is made by a small pair of glands called the parathyroid glands; and
calcitonin, which is secreted by the thyroid glands) regulate blood calcium
levels and bone metabolism.
At low concentrations PTH maintains a
stable level of mineral turnover in the bone, but at high levels it stimulates
osteoclast activity, thus releasing calcium into the bloodstream.
calcitonin counteracts the effects of PTH on osteoclasts, its functions and
mode of action are still poorly understood, but PTH affects bone, kidney,
and intestine using vitamin D as an intermediary—a point that returns us
to the contributions of sunlight and diet. Our diets and cellular machinery
provide inactive forms of vitamin D, but these require the direct energy
from sunlight hitting the skin to change into potentially active forms.
Final transformations from inactive to active forms of vitamin D occur in
the liver and kidney (Bezkorovainy and Rafelson 1996).
Although gonadal hormones—both estrogens and androgens—are
Physiological functions such as heart and breathing rate and energy metabolism are
regulated through involuntary nerves belonging to the sympathetic and parasympathetic
nervous systems. These systems balance each other out by stimulating or inhibiting various
functions. They are controlled through brain centers without our having to think about
All cells, but especially nerve and muscle cells, need calcium. So bone is essential not
only for structural support but also to maintain healthy calcium levels throughout the body.
The active form of vitamin D is 1, 25-dihydroxycholecalciferol.
Parathyroid hormone also increases Ca
reabsorption in the kidney and absorption
in the small intestine.
S I G N S Winter 2005 ❙1509
clearly important for bone development and maintenance, how they reg-
ulate bone metabolism remains uncertain (Kousteni et al. 2001, 2002).
Recently, some fascinating studies done on mice have suggested that both
androgens and estrogens operate in a fashion unusual for steroid hor-
mones—by preventing the death of bone-forming cells without stimu-
lating new gene activity. Whether these results will hold for humans re-
mains to be seen.
Other information from animal models suggests that
bone response to mechanical strain requires the presence of an estrogen
receptor on the osteoblast cell surface (Lee et al. 2003), but a clear story
of the role of estrogens and androgens in bone formation and maintenance
throughout the life cycle remains to be told.
Last but certainly not least a hormone called leptin, announced to the
world with great fanfare in 1995 as a possible “magic bullet” for weight
control (Roush 1995), also affects bone formation. Like the sex steroids,
leptin works via a relay system in the hypothalamus, a part of the brain
linked to the pituitary gland. Fat tissue produces leptin, which signals
specialized nerve cells in the hypothalamus; these activated neurons pro-
duce two effects—lowering the appetite and stimulating basal metabolism
(via the sympathetic nervous system). In mice, leptin has a second, ap-
parently independent effect, also mediated through the hypothalamus and
the sympathetic nervous system. Increased leptin signals nerves in the
bone to depress bone formation. This presents an interpretive paradox:
obesity provides some protection against osteoporosis. But the more fat
cells, the more leptin is made, which in theory ought to depress bone
formation. There are several possible explanations for this paradox. In
mice it may be that the very overweight body becomes insensitive to its
high leptin levels, just as obesity contributes to insulin insensitivity in type
2 diabetes. Or the stimulation of bone formation from the mechanical
stress of increased weight might trump the effects of leptin, and/or leptin
physiology in mice and humans might differ in important ways.
In the next decade we will surely learn a lot more about the relationships
among bone formation, leptin, and the sympathetic nervous system.
we also must learn how to study the balances and interactions among all
The negative effects of estrogen treatment come from the hormone’s more common
mode of action—stimulating gene activities after binding to the nucleus. The researchers
cited have a compound that has none of the gene-activity-stimulating actions but doesbehave
like androgens and estrogens by preventing the death of osteoblasts. See also Moggs et al.
Ducy et al. 2000; Flier 2002; Takeda et al. 2002; Harada and Rodan 2003.
Leptin may also regulate the onset of puberty, thus linking gonadal hormones and the
leptin hormone system (Chehab et al. 1997).
of the various factors that impinge on bone formation. How do social
systems that inﬂuence what we eat, how and when we exercise, whether
we drink or smoke, what kinds of diseases we get and how they are treated,
and how we age, to name some most relevant to bone formation, produce
a particular bone structure in a particular individual with a particular life
history? To even begin to set up this problem in a manner that can stim-
ulate future work and ultimately bring us better answers, we need to learn
how to handle complex, dynamic systems. And so, ﬁnally, I turn to a
discussion of two overlapping sets of ideas—developmental and dynamic
Thinking systematically about bone
There are better ways to think about gender and the bare bones of sex.
One cannot easily separate bone biology from the experiences of individ-
uals growing, living, and dying in particular cultures and historical periods
and under different regimens of social gender.
But how can we integrate
the varied information presented in this essay in a manner that helps us
ask better research and public policy questions and that, in posing better
questions, allows us to ﬁnd better answers? By better, I mean several things:
in terms of the science I want to take more of the “curious facts” about
bone into account when responding to public health problems. I favor
emphasizing lifelong healthful habits that might prevent or lessen the
severity of bone problems in late life, but I would also like us to have a
better idea of how to help people whose bones are already thin. What
dietary changes, what regimens of exercise and sun exposure, what body
mass index work best with which medications? How do the medications
we choose work? What unintended effects do they have? Finally, better
includes an ability to predict outcomes for individuals, based on their
particular life histories and genetic makeups, rather than merely making
probability statements about large and diverse categories of people.
How can we get there from here? Below, I outline in fairly general
form the possibilities of dynamic systems and developmental systems ap-
proaches. Such formulations allow us to work with the idea that we are
always 100 percent nature and 100 percent nurture. I further point to
I found one eloquent but wordless example on the Web in an article on causes of
vitamin D deﬁciency. The short segment titled “Insufﬁcient Exposure to Sunlight” was
accompanied by a photograph of two women, standing in the blazing sun, covered from
head to toe in burkas, clearly insufﬁciently exposed to sunlight but not for want of being
outdoors in the sun.
S I G N S Winter 2005 ❙1511
important theoretical and empirical work currently under way by social
scientists who study chronic diseases using a life-course approach. Before
turning to the speciﬁcs of bone development, let me offer a general in-
troduction to these complementary modes of thought.
Figure 2 presents a visual scheme of the larger systems arena. Ludwig
von Bertalanffy is usually cited as the originator of “general systems
theory,” a program for studying complex systems such as organisms as
whole entities rather than the traditional approach of reducing the whole
to its component parts (Bertalanffy 1969), but the idea of studying
developmental outcomes as a result of the combined action of genes and
environment began in the early twentieth century before a clear theoretical
statement was achieved in the 1940s.
Systems theorists also write about the brain and behavior. D. O. Hebb
(1949) linked psychology and physiology by thinking about how func-
tional cellular groups develop in the brain, thus developing a form of
systems theory called connectionism. As Esther Thelen and Linda Smith
put it, “the connection weights between layers—the response of the net-
work to a particular input—thus depend on the statistical regularities in
the network’s history of experiences” (Thelen and Smith 1998, 580). Thus
an organism’s current and future behaviors are shaped by past experiences
via a direct effect on the strength of connections between cells in the
The varied systems approaches to understanding development share
certain features in common. All understand that cells, nervous systems,
and whole organisms develop through a process of self-organization rather
than according to a preformed set of instructions.
The varying rela-
Brief histories of these ideas as well as accounts of present-day embryology, genetics,
and evolution based on systems theor y may be found in Waddington 1957; Kauffman 1993;
Webster and Goodwin 1996; Schlichting and Pigliucci 1998; van der Weele 1999; Oyama
The implications of these ideas for an integrative theory of the development of gender
differences in behavior and psychological skills has not escaped me and is the subject of a
work in progress. The explosion of knowledge about the plastic nature of brain development
and an increasing understanding of neuroplasticity in adults suggests that far from being
destiny, anatomy is dynamic history. A rich literature that joins mathematical models of
nonlinear equations (Kelso 1995) has begun to join forces with experimental scientists who
study animal behavior (Gottlieb 1997) and those who now use dynamic systems approaches
to reconceptualize human behavioral development (Smith and Thelen 1993; Thelen and
Smith 1994, 1998; Thelen 1995; Thelen et al. 2001).
Among biologists the idea that genes provide such instructions is giving way to a
systems account of cell function. The metaphor of the genome (DNA) as a blueprint or set
of directions for building cells and organisms is giving way to a new metaphor—genomes
Figure 2 Overview of systems theories
S I G N S Winter 2005 ❙1513
tionships among system components lead to change, and new patterns
are dynamically stable because the characteristics of the system confer
stability. But if the system is sufﬁciently perturbed, instability ensues and
signiﬁcant ﬂuctuations occur until a new pattern, again dynamically stable,
emerges. Bone densities, for example, are often dynamically stable in mid-
life but destabilize during old age; most medical interventions aim to
restabilize the dynamic system that maintains bone density. But we really
do not understand how the transition from a stable to an unstable system
of bone maintenance occurs.
To address the bare bones of sex, I highlight, in ﬁgure 3, seven systems
that contribute to bone strength throughout the life cycle.
scribe some of the known interrelationships between them.
the seven—physical activity, diet, drugs, bone formation in fetal devel-
opment, hormones, bone cell metabolism, and biomechanical effects on
bone formation—can be analyzed as a complex system in its own right.
Bone strength emerges from the interrelated actions of each (and all) of
these systems as they act throughout the life cycle. As a ﬁrst step toward
envisioning bone from a systems viewpoint we can construct a theoretical
diagram of their interactions. The diagram in systems approaches can be
thought of as a theoretical model, to be tested in part or whole and
as parts list (Vukmirovic and Tilghmann 2000; Tyson, Csikasz-Nagy, and Novak 2002). If
the genome lists only the component parts (codes for RNA and protein), the location of
the assembly directions becomes uncertain: one needs to specify a cell or organism’s past
history and current conditions in order to predict a current developmental event accurately.
Cell biologists have now turned in earnest to complexity and systems theory to help learn
the rules by which organisms are assembled. (See entire December 2002 issue of Bioessays
devoted to “Modeling Complex Biological Systems.”) In another example, authors extend
and twist the book metaphor: “Just as words must be assembled into sentences, paragraphs,
chapters and books to make sense, vital cellular functions are performed by structured en-
sembles of proteins . . . not by freely diffusing and occasionally colliding proteins” (Sali et
al. 2003, 216).
I use Peter Taylor’s deﬁnition of systems as “units that have clearly deﬁned boundaries,
coherent internal dynamics, and simply mediated relations with their external context” (per-
sonal communication 2003).
This choice of systems emerges from the data presented earlier in this article. Since
this is a model, others might argue for dividing the pie in a different way. To keep the
diagram readable and the discussion manageable, I have not emphasized that the entire
grouping of systems is embedded in a larger system I call “general health.” There are many
disease states that secondarily affect bone (e.g., kidney disease or endocrine disorders) by
affecting calcium metabolism or preventing exercise. The relationships among the systems
affecting bone strength would be shifted in dramatic ways worthy of study in their own right
under such circumstances.
Figure 3 A life history–systems over view of bone development. (1) Physical activity has
direct effects on bone cell receptors and indirect effects by building stronger muscles, which
exert physical strain on bones, thus stimulating bone synthesis. (2) Physical activity that takes
place outdoors involves exposure to sunlight, thus stimulating vitamin D synthesis, part of
the hormonal system regulating calcium metabolism. (3) Biomechanical strain affects bone
cell metabolism by activating genes concerned with bone cell division and bone (re)modeling.
(4) Hormones affect bone cell metabolism by activating genes concerned with bone cell
division, cell death, bone (re)modeling, and new hormone synthesis.
S I G N S Winter 2005 ❙1515
modiﬁed as needed.
As ways to describe each component system using
numerical proxies become available, the pictorial model can provide the
framework for a mathematical model. Figure 3 represents one possible
diagram of a life-course systems account of bone development.
This feminist systems account embeds the proposed subsystems within
the dimensions of gender, socioeconomic position, and culture.
the diet system. Generally, of course, diet is shaped by culture and sub-
culture, including race and ethnicity (Bryant, Cadogan, and Weaver 1999).
But gender further inﬂuences diet. For example, one study reports that
27 percent of U.S. teenage girls (compared with 10 percent of adolescent
boys) who think they weigh the correct amount are nevertheless trying
to lose weight (Walsh and Devlin 1998). It may also be true that there
are sex/gender differences in basal metabolism rates that inﬂuence food
Figure 3 also indicates the cumulative effects of diet on bone formation.
Key events may be clustered at certain points in the life cycle.
ample, adolescent girls in the United States often diet more and exercise
less than during earlier childhood. Diseases such as anorexia nervosa,
which have devastating effects on bone development, may also emerge
during adolescence. As Yoav Ben-Shlomo and Diana Kuh (2002) point
out, such clustering of adverse events is common and may be thought of
in terms of “chains of risk” (or beneﬁt). In a life-course approach, prior
events set the limits on later ones. If girls and women enter into adulthood
with weakened bones, therefore, they can rebuild them, but their peak
density may be less than if they had built stronger bones in adolescence.
Alternatively, achieving a safe peak bone density might require more sus-
tained and intense work for a person of one history compared with a
person of a different history.
Sex/gender, race, class, and culture also differentiate individuals by forms
of play in childhood and beyond (Boot et al. 1997), by choices of formal
exercise programs, and, in adulthood, by forms of labor, physical and
otherwise. In analyzing the system of physical activity one again applies
life-course principles by considering that what happens at any one point
Choice of model has profound implications. For a discussion of a lifestyle model of
disease that emphasizes individual choice vs. a “social production model,” see Krieger and
Zierler 1995. For an update on current theories of social epidemiology, see Krieger 2001.
To the extent that race is a legitimate category separate from class and culture, I will
incorporate it into the bone systems stor y in pt. 2 of this work. For a model of social pathways
in childhood that lead to adult health, see Kuh and Ben-Shlomo 1997.
Bonjour et al. 1997; Boot et al. 1997; Perry 1997; Wang et al. 2003.
For the effects of dietary calcium later in life, see Heaney 2000.
builds on what has gone before. Important events with regard to bone
development may be clustered and interrelated. For both the diet and
physical activity systems, it should be possible to design mathematical
models based on some measure of bone strength that would incorporate
the effects of each of these social systems on bone development through-
out the life cycle; once we have plausible models of each system, we can
ask questions about their interactions.
The remaining four systems are often considered within the realm of
biology, as if biology were separate from culture, although recent work
from some medical epidemiologists challenges this distinction (Ellison
1996; Hertzman 1999; Lamont et al. 2000). The system of biomechanical
effects on bone synthesis, for example, requires further investigation of all
of its inputs (physical strain, activation of genes that stimulate bone cell
development or death, etc. [Harada and Rodan 2003]), but these must
then be studied in relationship to the gender-differentiated physical activity
system. The different body shapes of adult men and women (related to
hormones at puberty among other things) may also affect bone biome-
chanics, and we need, too, to know more about how growth and devel-
opment affect the number of bone mechanoreceptors—molecules that
translate mechanical stress in biochemical activity (Boman et al. 1998;
Pavalko et al. 2003).
The impact of hormones on bone development and maintenance re-
quires research attention of a sort currently lacking in the bone literature.
We need to know both about the molecular biology of hormones and
bone cell hormone receptors and about life-course effects on hormone
systems (Ellison 1996; Worthman 2002). Finally, genes involved in bone
cell metabolism, pattern formation, hormone metabolism, drug process-
ing, and many other processes contribute importantly to the development
of bone strength (Zelzer and Olsen 2003). Understanding how they func-
tion within both the local and global (body and sociocultural) networks
contributing to bone development requires a systems-level analysis not
yet found in the literature.
This article is a call to arms. The sex-gender or nature-nurture accounts
of difference fail to appreciate the degree to which culture is a partner in
producing body systems commonly referred to as biology—something
apart from the social. I introduce an alternative—a life-course systems
approach to the analysis of sex/gender. Figure 3 is a research proposal
for multiple programs of investigation in several disciplines. We need to
S I G N S Winter 2005 ❙1517
ask old questions in new ways so that we can think systematically about
the interweaving of bodies and culture. We will not lay bare the bones of
sex, but we will come to understand, instead, that our skeletons are part
of a life process. If process rather than stasis becomes our intellectual goal,
we will improve medical practice and have a more satisfying account of
gender and sex as, to paraphrase the phenomenologists, being-in-the-
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Feminist Philosophy.” Signs: Journal of Women in Culture and Society 25(3):
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in Black Women.” Calciﬁed Tissue International 59(6):415–23.
Armelagos, George J. 1998. “Introduction: Sex, Gender and Health Status in
Prehistoric and Contemporary Populations.” In Sex and Gender in Paleopath-
ological Perspective, ed. Anne L. Grauer and Patricia Stuart-Macadam, 1–10.
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