Emerging Trends in The Social and Behavioral Sciences

Social Neuroendocrine Approaches to Relationships

Item

Title

Social Neuroendocrine Approaches to Relationships

Author

van Anders, Sari M.

Gray, Peter B.

Research Area

The Individual and Society

Topic

Social Interactions in Everyday Life

Abstract

Social neuroendocrinology is the study of social behaviors and hormones, using ultimate (evolutionary) and proximate (mechanistic) considerations, alongside social context. In this entry, two scholars from psychology and anthropology focus on social relationships (e.g., parenting, romantic relationships, sexual contacts) and both peptide (e.g., oxytocin, vasopressin) and steroid hormones (e.g., testosterone, estradiol, cortisol). Basic theoretical underpinnings of social neuroendocrinology are discussed, along with classic and cutting edge scholarship alongside newer theories. The challenges and promises of social neuroendocrine approaches to relationships are detailed, with an eye to the future of the discipline.

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Identifier

etrds0309

extracted text

Social Neuroendocrine Approaches
to Relationships
SARI M. van ANDERS and PETER B. GRAY

Abstract
Social neuroendocrinology is the study of social behaviors and hormones, using
ultimate (evolutionary) and proximate (mechanistic) considerations, alongside
social context. In this entry, two scholars from psychology and anthropology focus
on social relationships (e.g., parenting, romantic relationships, sexual contacts) and
both peptide (e.g., oxytocin, vasopressin) and steroid hormones (e.g., testosterone,
estradiol, cortisol). Basic theoretical underpinnings of social neuroendocrinology are
discussed, along with classic and cutting edge scholarship alongside newer theories.
The challenges and promises of social neuroendocrine approaches to relationships
are detailed, with an eye to the future of the discipline.

INTRODUCTION
Social relationships provide meaning and structure to our lives; they are the
foundation for our families, friendships, workplace hierarchies, sexual contacts, and loving relationships. They impact our health and well-being, and
teach us about the cultures we live in. Human social neuroendocrinology
is the study of these types of social relationships, using a hormonal lens.
Social neuroendocrinology provides fascinating insights into the ways that
hormones influence our social relationships and, in addition, how our social
relationships affect our hormones. But, social neuroendocrinology is not just
about biology. It also sheds light on cultural processes and pays attention to
social experiences. This interactionist lens contributes to an ongoing reshaping of knowledge that incorporates both nature and nurture, biology and
culture, evolution and social construction.
We focus specifically on two kinds of social relationships in this article: (i)
adult-infant interactions such as those between parents and children and (ii)
adult partnering, such as pair bonds or romantic/sexual relationships. Many
aspects of our social relationships are unique to humans, whereas some are

Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

shared with other animals ranging from birds to rodents to nonhuman primates, and more. Those features common across species allow scientists to
study the evolved neurobiological systems that may be a common denominator in social relationships, albeit with attention to the uniqueness of each
species and taxa.
Social neuroendocrine perspectives on relationships draw on a number
of theoretical foundations. One of these was advanced by Niko Tinbergen
in the early 1960s. Tinbergen outlined how questions in biology can be
answered via four complementary levels of analysis: phylogeny (evolutionary history), function (adaptive explanations), mechanism (physiological
causal processes), and ontogeny (development; changes across the lifespan).
When we ask why an association between hormones and social relationships
exists, we are asking an ultimate question that is answered via research on
phylogeny and function. When we ask how this association exists, we are
asking a proximate question that is answered via research on mechanism and
development.
Another important theoretical foundation for social neuroendocrinology is
attachment theory, associated with John Bowlby and Mary Ainsworth. Here,
the notion is that humans are born with the goal of forming social bonds
with parental figures, because these are adaptive in promoting child survival.
Attachment is thought to drive much of social motivation and influences
other close social bonds. And, it means that social relationships of various
kinds are thought to share common features and even hormonal systems
with parent-infant bonds.
A third foundation for social neuroendocrinology is based on scientific
and agricultural experimentation with hormones. This is largely understood
to have originated in the nineteenth century with Arnold Berthold, who
transplanted testes from one species to another. However, recognition
that something in the body could influence social relationships has a
deep history, with castration of humans and other animals a longstanding
practice. Insights into what this “something” might be, however, arrived in
the twentieth century with the identification of steroid hormones such as
testosterone (secreted mainly from the testes or ovaries). This fostered the
development of behavioral neuroendocrinology; the study of hormones and
a broad range of behaviors.
Social neuroendocrinologists are largely interested in steroid hormones
and peptide hormones, which have pleiotropic—or multiple—functions that
are not limited to social relationships. Steroids are released from hormonal
glands and bind to hormone receptors located throughout the body and
brain. Androgens (e.g., testosterone), estrogens (e.g., estradiol), and glucocorticoids (e.g., cortisol) are the steroid hormone groups largely studied in
social neuroendocrinology. A mistaken belief is that androgens exist in men

Social Neuroendocrine Approaches to Relationships

3

and estrogens in women; in fact, both groups of hormones are functional
and present in women and men. Peptides are released from the pituitary
gland in the brain, and bind to specific receptors located throughout the
body and brain. Oxytocin, prolactin, and vasopressin are important peptide
hormones that, within social neuroendocrinology, are largely studied in
relation to attachment.
Hormones are actually released in response to signals from the brain. The
brain’s hypothalamus sends releasing signals to hormonal glands based on
an integrated mix of incoming messages from the rest of the brain, reflecting
the social environment, and actual hormone levels in the body. That’s one reason why social neuroendocrinology is interactionist, that is, that hormones
respond to internal (in the body) and external (e.g., social) phenomena.
Social neuroendocrinology uses a broad set of methods to assess how hormones and social relationships are associated. For example, some scientists
conduct experiments to determine effects of hormone on behavior. Others
experimentally examine how social behavior affects hormones. Still others
use correlational studies, group differences, or other neuroscience techniques
such as genetics or neuroimaging. Research might occur in the laboratory
or in the field. At its core, social neuroendocrinology is an interdisciplinary
endeavor that draws on perspectives from multiple fields. It provides important insights about hormones and social relationships, and the evolutionary
and cultural context in which our social relationships develop.
FOUNDATIONAL RESEARCH
One of the most important insights from social neuroendocrinology is that
social relationships can profoundly influence not only whether we feel loved
or supported, but also can reshape our very biologies. For example, rat
mothers engage in a variety of maternal behaviors, including pup licking,
that differ in frequency. As scientists have found, pups who were maternally
licked more frequently had different DNA methylation patterns compared
to low-licked pups, leading to epigenetic alterations of the glucocorticoid
receptor and impacting stress physiology.
Although parents can exert such strong effects on offspring, infants can
actually affect their caregivers as well. Studies have shown that attachment
behaviors (e.g., close touch, warm support) increase oxytocin and decrease
cortisol in both parents and children. This is thought to occur because the
physiology of caregiving seems to “borrow” from evolutionary systems that
underlie reproductive processes. For example, peptides such as oxytocin and
prolactin underlie lactation and birth, but also are implicated in attachment.
Estrogens and progesterone are intrinsic to ovulation and pregnancy, and
ratios between them seem important to maternal feelings during and after

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pregnancy. Of course, pregnancy, birth, breastfeeding, and the postpartum
are not merely hormonal or reproductive events themselves; they are also
social experiences. However, research on breastfeeding suggests that it has
hormonally mediated benefits for mothers in addition to nutritional and
attachment benefits for children: it increases and/or decreases cortisol and
stress responsivity in ways that seem to reduce stress and facilitate bonding.
There has been an explosion of interest into how peptides might mediate
attachment between parents and infants. In part, this is based on research
with species that, such as humans, develop close social bonds. The most
well-known model species is the prairie vole, that forms close parental and
pair bonds. In comparison to the closely related montane vole, prairie voles
show higher density of peptide receptors that have been experimentally
shown to support bonding behavior. Although social bonds do not work in
the same way across all species or contexts, and also do not necessarily rely
on the same neurobiological substrates, this research on social bonds has
been pivotal for human studies. Indeed, Sue Carter published a landmark
paper in the field that turned “love” into a respectable topic for neuroscience.
What does research with humans show? Prolactin actually increases in
response to infant stimuli in pregnant women, even before they have
children. After birth, mothers and fathers show bigger oxytocin increases
if they had more affectionate or stimulatory contact. And, higher oxytocin
seems to be related to more sensitive caregiving in women and men. Indeed,
parents with high levels of certain peptides seem to engage with their infants
in ways that reflect more synchrony, or matching of play styles or affect.
Still more research suggests that mothers with higher oxytocin responses to
infants are also more sensitive to affective and physical phenomena.
The above research demonstrates how individual differences in peptide
levels or responses are associated with differences in attachment-related
behaviors. Research has also demonstrated that administration of peptides
may have similar effects. Intranasal oxytocin administration to fathers seems
to have small effects on paternal behaviors with toddlers, like decreases
in hostility. This research is still somewhat controversial, however, as
many scientists question whether intranasal peptide administration can
actually affect the brain because of the blood brain barrier. What about
the infants? Research has suggested that oxytocin administration to parents
increases a set of behaviors that are known to support parent-infant bonds,
and—also—increase oxytocin and engagement in the infants themselves.
Conversely, socially-deprived children who were orphaned and subsequently adopted into caring families exhibited alterations in their oxytocin
and vasopressin systems.
Cortisol is better known as a stress hormone, but its function is actually more
broad, relating to activation and arousal in general. Interestingly, peptides

Social Neuroendocrine Approaches to Relationships

5

seem to dampen cortisol release. Cortisol is related to intimacy in interesting ways. For example, high cortisol has been linked to lower engagement
in attachment behaviors. But, high cortisol early in the postpartum is actually
associated with more attentive maternal behavior. This makes sense: it would
be adaptive, on hearing an infant shriek, to feel a sense of activation rather
than relaxation (at least for the infant!). Accordingly, whether cortisol’s association with caregiving is more or less valuable may depend on the given
caregiving culture and situation.
Although infant interactions affect parental hormones, parents also seem
to differ hormonally from nonparents in a variety of ways. For example,
some evidence shows that fathers and mothers have lower testosterone than
nonparents. This is largely interpreted via the “challenge hypothesis,” which
predicts that high testosterone should be linked with challenge and mating,
while low testosterone should be linked to parenting. Although developed
with birds, it has been extended to a number of species, including humans.
Fathers also differ hormonally from nonfathers in a variety of ways. In several other nonhuman mammals, such as common marmosets, fathers have
been found to have higher prolactin levels. A study of Filipino men found
that fathers had higher prolactin levels than nonfathers, the first time that
had been shown in humans.
The challenge hypothesis is also used to make sense of the ways in which
testosterone is linked to adult social bonds, like romantic/sexual relationships. Research from a number of labs has demonstrated that single, heterosexual men and women have higher testosterone than their partnered counterparts. This partnering can be marriage, cohabitation, or even long-term
relationships, and classic research first demonstrated the phenomenon using
participants from the army or air force, including a transient increase around
divorce in men. There is also evidence that cortisol levels are high in couples newly in love, highlighting further that “stress” reflects perturbations of
homeostasis even in positive situations.
Hormones are often fingered as the cause of lust, love, and other related
phenomena. It would be an exaggeration to claim a large role for them in
humans, but scientists have demonstrated fascinating if modest associations between hormones and the phenomena that underlie romantic and
sexual relationships. Research links peptides with phenomena like trust or
closeness that underlie pair bonds. Because many of the same phenomena
underlie pair bonds and parent-infant bonds, scientists have been excited
about findings that demonstrate overlapping neural substrates involved in
both. For example, viewing pictures of a beloved partner and a loved infant
results in neural activation in divergent areas but also some overlapping
ones that are known to be dense in oxytocin and vasopressin receptors. Thus, hormonal systems related to reproduction seem to have been

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

“borrowed” for parent-infant bonds, and also for pair bonds. As examples,
a number of studies identify links between the oxytocin system and aspects
of pair bonds. Women and men reporting higher marital quality had higher
blood oxytocin levels than individuals reporting lower marital quality,
and oxytocin increased with warm partner contact. Oxytocin levels are
higher in new lovers relative to singles. And, showing causal links between
oxytocin and pair bonds, the administration of intranasal oxytocin positively
impacted partner interactions during a standardized marital discussion. Of
course, pair bonds are characterized by more than just bonding—sexuality
plays an important role too.
Orgasm and sexual behavior also increases oxytocin and other peptides.
Perhaps this relates to oxytocin’s role in mediating muscular contractions in
parity-related events, like uterine contractions for birth and milk ejection in
breastfeeding. Other hormones are also implicated. Estradiol, an estrogen,
seems to be correlated with affiliative phenomena, like sexuality.
Testosterone is another hormone that is often linked with sexuality. Indeed,
it does increase following exposure to sexual stimuli, engagement in sexual
activity, and even sexual thoughts. In fact, testosterone seems to respond to
sexuality more strongly than it influences sexuality in humans. For example,
researchers found that heterosexual men engaged in flirtatious behavior with
women had an increase in testosterone.
A separate line of research examines attraction to potential partners across
the menstrual cycle. The idea is that during fertile times of the menstrual
cycle, when estrogen and androgen levels rise, women may exhibit changes
in the characteristics they seek in a partner. In one review, women showed
increased attention to masculine faces and voices during their fertile menstrual phase. Other studies suggest that women’s sociosexual behavior can
also shift during fertile phases. The observation of these kinds of cycle-related
effects suggests they are subtle, and studies employ variable methodological rigor (e.g., definition of cycle phases, whether hormones are measured
or not).
There are a number of important findings from social neuroendocrinology
on relationships, ranging from romantic contacts to parent-infant bonds.
These have led to novel insights about the role of hormones in human social
connections. However, as researchers delve more deeply into these newly
discovered phenomena, sometimes well-accepted findings are turned on
their head even as others are more decisively confirmed.
CUTTING EDGE RESEARCH
Do fathers have lower testosterone than nonfathers? Does oxytocin promote
love? Do singles have higher testosterone than married folks? Do menstrual

Social Neuroendocrine Approaches to Relationships

7

shifts in psychology occur? Cutting edge research in social neuroendocrinology addresses the nitty-gritty details and truth-value of these claims. For
example, peptides are largely thought of as “prosocial,” meaning that they
are always “good” in relation to social bonds. But, researchers are finding
that empirical evidence is actually more complicated than the initial story
suggested. Thus, even though oxytocin is thought to promote social bonds,
it also seems to reflect a need for social bonds: women with self-reported
poorer relationship functioning have higher oxytocin than women who
are satisfied with their relationships. Evidence suggests that oxytocin may
amplify social affect. In this case, one could easily imagine how oxytocin
administration might amplify undesirable aspects of social bonds. Moreover, context is increasingly understood to matter. For example, oxytocin
administration lessens an overharsh grip strength in response to hearing
infant cries, but only among women who were not harshly disciplined
themselves as children.
Of course, context is not just background or mood states. It can also be
physiological, and behavioral genetics work in social neuroendocrinology
has demonstrated just this. For example, though oxytocin administration can
increase preference for infant faces, it does so only in individuals with a specific polymorphism on the gene that codes for oxytocin receptors. Differences
in the vasopressin 1a receptor have been associated with partner bonding
behaviors. However, those associations were only true of men.
Even hormones can be a context for each other, and scientists are increasingly attending to interactions between hormones and their implications for
social relationships. In one such framework, the steroid/peptide theory of
social bonds (S/P theory), peptides are related to social bonding phenomena,
including even negative behaviors that might be related. In contrast, testosterone is negatively associated with nurturant social bond phenomena, and
positively associated with competitive behaviors that are aimed at acquiring
or defending resources (that may include social or sexual bonds themselves!).
Another integrative theory—the Dual Hormone Hypothesis, has been used
around competition and is less used around social relationships, though is
promising. It predicts that testosterone is linked to social behaviors in ways
that are mediated by cortisol levels.
One perplexing finding in social neuroendocrinology has been that infant
cries increase testosterone and that testosterone can upregulate neural areas
involved in parental care, in contrast to most theoretical predictions. More
recent research has demonstrated that nurturant behaviors while hearing
infant cries does decrease testosterone, as predicted by the S/P theory.
Scientists are increasingly attending to the specificities of the behavior under
investigation, in ways that shed light on their associations with hormones.
For example, though parents sometimes have lower testosterone than

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nonparents, they sometimes have higher testosterone. This may be because
some parenting involves nurturance and direct care, while some involves
competitive behaviors and indirect care. Research does suggest that parents
of younger children who are more involved in nurturant care are the ones
with lower testosterone.
Relationships, too, are linked to testosterone in more nuanced ways.
Marriage is likely a proxy at best for the underlying constructs related
to testosterone. Cross-cultural research has highlighted that partnering
is not the same world over, and sometimes even pair bonds involve the
possibility of new partners. In this way, research has shown that, whether
in a relationship or not, interest in new or more partners is associated
with higher testosterone in men, whereas presence of more partners or
more sexual behavior is associated with higher testosterone in women.
Indeed, one interesting outcome of this research has been the suggestion
that testosterone is linked to relationship status in women, but relationship
orientation in men. This body of research shows that relationships are diverse
and can involve commitment and/or extra-pair sexuality and that it is these
nuances that seem to clarify how specific kinds of relationships are linked to
hormones.
What about relational dynamics themselves? A variety of studies have
investigated links between cortisol and partner quality. Some studies test
whether patterns of cortisol concentrations across the day are related to
partnership factors; more partner intimacy was associated with lower cortisol profiles in a naturalistic study. Other studies led by Kiecolt-Glaser and
Glaser at The Ohio State University have entailed younger and older couples
reporting to a lab to engage in a standardized marital conflict discussion
session, testing effects of partner discussions on cortisol profiles. As an
example, the marital satisfaction reported by wives was inversely related
to their cortisol change across a marital discussion, with more satisfied
wives showing more rapid cortisol declines. In addition, a study noted
above observed that intranasal oxytocin decreased cortisol levels during
marital discussions, showing the relationships between oxytocin and stress
hormone reduction.
Though sexual desire is largely assumed to be clearly related to testosterone, research actually shows that desire itself is more complicated. For
example, studies have found that solitary sexual desire, or desire to masturbate, is positively correlated with testosterone in women, but not men,
whereas dyadic sexual desire, or desire to be sexual with another person,
is negatively correlated in women but not men. Social neuroendocrinology
helps to highlight what desire is actually about, as desire may reflect interest in intimacy, closeness, orgasm, sleep, and so on. It may be that desire for
intimacy maps onto lower testosterone, and desire for erotic pleasure maps

Social Neuroendocrine Approaches to Relationships

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onto higher testosterone. Interestingly, these results hold only for women.
Research on sexual desire and testosterone in healthy men shows no significant correlation between testosterone and desire in healthy men despite
longstanding assumptions to the contrary.
The postpartum is often a time for parent-infant bonding, but this still
occurs—for many people—within the context of an adult relationship like
marriage. Indeed, changes in relationships are a hallmark of the postpartum
for most parents. There is some belief that decreases in partnered sexual
behavior or sexual desire may map onto the hormonal processes associated
with parity. There is also evidence that social changes associated with the
new parenting roles, relationship structures, and having a new baby are
related to postpartum sexuality in both mothers and coparents. And, though
researchers have generally focused on low sexual desire and infrequent
sexual activity during this time, evidence suggests that many birth mothers
are actually engaging in a variety of sexual behaviors at this time. What
might be most interesting about postpartum sexuality, however, is how
similarly birth mothers and their coparents experience it. This suggests that
hormones, if involved, may be reacting to the social changes around birth
rather than the birth-specific reproductive events themselves.
Recent cutting edge research in social neuroendocrinology had tended to
add more “grey” to early “black-and-white” findings, adding nuance and
contextual considerations. In addition, this body of literature is attending
more closely to the details of the social phenomena under study to get to the
core of what it is about relationships, desire, or parenting, as some examples,
that is reliably linked to hormones. Finally, the most up-to-date research
takes a more skeptical stance, not undermining that hormones and social
behaviors are meaningfully and interestingly connected, but attending to a
fuller realm of possible links including null associations, moderation, and
counter-expected associations.
KEY ISSUES FOR FUTURE RESEARCH
Social neuroendocrine approaches to relationships are so new that a number
of key issues have only recently been identified. For example, the focus
on a limited set of social relationships (like marriage, parent–child bonds,
etc.) limits our understanding of all social relationships. Attending to relationships like friendships, grandparenting, adoptive- and step-parenting,
nonparental childcare, sibling care, mentoring, and even human-pet interactions will likely be informative. And, though research has often focused
on hormonal mediation of the positives of human social relationships, like
love, intimacy, and attachment, there are a number of “negatives” that
merit investigation too. For example, how might social neuroendocrinology

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help us understand child neglect, partner abuse, rape, or intrafamilial
aggression? Moreover, participants in social neuroendocrinology tend to be
adults, or a focus on adult–infant bonds. It remains to be seen whether the
same hormonal processes are tied to caregiving of older children, much less
teenagers or adult offspring.
There are a number of additional axes along which differences can and
likely will matter. For example, the majority of social neuroendocrinology,
especially about hormones and parent-infant bonds, has been conducted
with “WEIRD” populations. But individuals who are white, educated, industrialized, rich, and democratic make up a very narrow slice of human diversity.
Basic research that presumes “good” or “bad” aspects of social bonding will
need to reconcile these notions with parenting across cultures (and within
Western nations) that have different norms. But, relatedly, research that
more explicitly addresses the applied implications of social neuroendocrine
studies of social relationships will also be important. This will require
acknowledging that social neuroendocrinology has sometimes erred on
the side of focusing on universal generalities rather than local specificities,
because applications are potential solutions to particular problems that are
generally culture-bound. Addressing both cultural diversity and cultural
specificity will thus be an important next step in both exploring the basic
social neuroendocrinology of relationships and its exciting applied potential.
Both basic and applied research require attending to cause and effect.
Currently, perhaps because of the scientism inherent in incorporating hormonal and biological measures into research, scientists are largely studying
how hormones might influence social bonds or using that arguable biologically deterministic perspective. This lens is but one approach, however,
because biology need not be biologically deterministic or unidirectional.
Other exciting cutting-edge biological approaches include epigenetics (how
experiences modify genetic processes), social determinants of health, and
phenotypic plasticity (e.g., how experience shapes the brain and body).
For social neuroendocrinology, attending to these perspectives include
addressing how social bonding processes affect hormones, and interactionist questions of how social relationships and hormones mutually influence
each other. Moreover, hormone administration studies have been conducted
with a generally narrow frame. For example, work on intranasal oxytocin
or vasopressin sprays is interesting, but it is still far from clear whether
they have central actions. And, because scientists largely focus on only their
prosocial effects, “side” effects and undesirable outcomes remain largely
unstudied despite concerning research pointing to them.
The focus on WEIRD populations has not been as prevalent in research on
testosterone and partnering, perhaps because this field includes researchers
from biological anthropology as well as psychology and neuroscience. This

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body of research demonstrates the importance and value of attention to culturally diverse forms of partnering. In addition, by incorporating individuals
who are lesbian, gay, bisexual, polyamorous, and in open relationships, it
highlights how sexual diversity, in addition to cultural diversity, is illuminating. Even WEIRD populations are not only single or married, and relational
approaches may be diverse. In fact, one could amend the term to WHEIRD,
with “H” signifying heterosexual. The majority of research focuses on one
specific kind of gendered pair bonds, but sexualities are broader than this.
Attention to bisexuality, same-sex sexuality, and even sexual fluidity will be
important. A growing movement of individuals to define an asexual identity
highlights diverse relational and sexual bonds, which will be important for
social neuroendocrinology to include. For example, demi-sexuals are individuals who experience sexual attraction to a person only after romantic connections. How might this map onto social neuroendocrine systems for social
and/or sexual connections? A key challenge for social neuroendocrinology
will be to attend to diversity rather than difference. For example, instead of
asking whether gay and straight men show similar neural responses to loved
ones, the field might ask how gendered sexuality is implicated among other
variables, and alongside socialization factors, in hormone-behavior associations. Indeed, socialization and social constructs remain understudied but
powerful lenses for social neuroendocrinology.
For those interested in understanding developmental trajectories, what is
strongly needed is a life course or life history perspective. For example, do
early parent-infant bonds have effects on hormonal systems in ways that
influence adult social bonds? Puberty is also increasingly recognized as a
period of hormonal plasticity, but remains understudied in human social
neuroendocrinology. Indeed, cause and effect remains to be hammered out
in a number of contexts. Longitudinal studies tend to be designed to answer
other questions, and often end up answering part but not all of this question.
Accordingly, life course studies would be informative.
The field would also benefit from increased comparative attention. At
present, there is already a large influence of nonhuman animal research on
human research. This makes sense, because there are a number of questions
that can only be answered with animal models. However, a comparative
approach requires attending to species-specificities. Accordingly, research
from one species can only inform understandings of another—it cannot be
immediately generalized. Already, there is clear evidence that the hormonal
and neurobiological substrates of social bonding are not the same across
species. For example, oxytocin and vasopressin receptor density underlie
differences between monogamous and multisexual voles, but not birds or
even other rodents. If the same hormonal processes do not underlie social
bonds among different rodents, it is obviously difficult to translate them

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

to humans. At the same time, understandings from other species may help
shed light on underlying processes, and are sometimes absent when they
could be helpful. For example, work with nonhuman primates shows both
similarities and differences in the hormonal mechanisms associated with
paternal care compared with humans.
Also missing is neural work that is conducted alongside hormonal studies. Research on neural imaging has largely relied on imaging those areas
already known to be implicated in social bonds—in other species. But, given
that these areas may not translate even to other rodents, there may be a host of
neural structures relevant in humans that current science is missing. Future
research will need to incorporate multiple methods into the same studies,
for example examining hormonal and neural changes to social bond stimuli alongside each other. Coupled with a life course approach, this could be
very powerful. For example, how might neural and hormonal responses to
infant stimuli differ after extensive caretaking experience or social bonding,
compared to controls?
Methodological issues abound in social neuroendocrinology, and need
attention for the field to move forward in rigorous ways. For example,
cortisol and testosterone exhibit large diurnal variation but it is unclear
how dynamic other socially relevant hormones might be. There are also
sampling issues, including how closely tied measures from fluids like
saliva, blood, urine, or cerebrospinal fluid might be and how well each
represents central (i.e., brain) activity. Some methodological reviews have
addressed these concerns but are constrained by what limited methodological research exists. Thus, a key task for social neuroendocrinologists will
be to incorporate methodological questions and sophistication into their
research.
The future of social neuroendocrinology is bright. As more researchers from
a variety of disciplines and sub-disciplines understand the value and ease
of incorporating hormone measures into their work, social neuroendocrine
work on relationships will continue to grow and become integrated into other
fields. Work is becoming increasingly sophisticated and nuanced, leading to
insights about hormones themselves, social relationships, evolutionary considerations, proximate mechanisms, and potential applications to real-world
problems.
FURTHER READING
Adkins-Regan, E. (2005). Hormones and animal social behavior. Princeton, NJ: Princeton
University Press.
Bartz, J. A., Zaki, J., Bolger, N., & Ochsner, K. N. (2011). Social effects of oxytocin in
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SARI M. van ANDERS SHORT BIOGRAPHY
Sari M. van Anders, PhD, is an Assistant Professor of Psychology and
Women’s Studies at the University of Michigan, and affiliated with UM’s
programs in Neuroscience, Reproductive Sciences, Science, Technology, and
Society, and the Biosocial Methods Collaborative. In the Social Neuroendocrinology Lab, Dr. van Anders studies hormones and social behaviors
in social context, paying special attention to sexuality, intimacy, and nurturance. Dr. van Anders’ PhD is in behavioral neuroscience, earned at
Simon Fraser University in Canada, in 2007. With over 50 publications in
social neuroendocrinology, health, gender/sex, and sexual diversity, Dr. van
Anders focuses on feminist and inclusive research practices. Dr. van Anders
is the Editor-Elect of the Annual Review of Sex Research and, in 2013, Dr.
van Anders received the Janet Taylor Spence Award for Transformative
Early Career Contributions from the Association for Psychological Science.
PETER B. GRAY SHORT BIOGRAPHY
Peter B. Gray, PhD, takes an integrative evolutionary perspective of
human reproduction. This means drawing on comparative nonhuman
findings, cross-cultural research, neuroendocrine mechanisms, and life
history theory to make sense of our behavior. He most thinks about how
an evolutionary perspective makes sense of human sexuality, fatherhood,
and even pet-keeping. He earned BA degrees in Anthropology and Geography/Environmental Studies at UCLA and a PhD in Biological Anthropology
in 2003 from Harvard University, also undertaking postdoctoral research
in Clinical Endocrinology. He has coedited (2009) “Endocrinology of
Social Relationships,” and coauthored “Fatherhood: Evolution and Human
Paternal Behavior” and “Evolution and Human Sexual Behavior,” all with
Harvard University Press.

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Patterns of Attachment across the Lifespan (Psychology), Robyn Fivush and
Theodore E. A. Waters
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Social Neuroendocrine Approaches to Relationships

15

Grandmothers and the Evolution of Human Sociality (Anthropology), Kristen
Hawkes and James Coxworth
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Cultural Neuroscience: Connecting Culture, Brain, and Genes (Psychology),
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Primate Allomaternal Care (Anthropology), Stacey Tecot and Andrea Baden



Social Neuroendocrine Approaches
to Relationships
SARI M. van ANDERS and PETER B. GRAY

Abstract
Social neuroendocrinology is the study of social behaviors and hormones, using
ultimate (evolutionary) and proximate (mechanistic) considerations, alongside
social context. In this entry, two scholars from psychology and anthropology focus
on social relationships (e.g., parenting, romantic relationships, sexual contacts) and
both peptide (e.g., oxytocin, vasopressin) and steroid hormones (e.g., testosterone,
estradiol, cortisol). Basic theoretical underpinnings of social neuroendocrinology are
discussed, along with classic and cutting edge scholarship alongside newer theories.
The challenges and promises of social neuroendocrine approaches to relationships
are detailed, with an eye to the future of the discipline.

INTRODUCTION
Social relationships provide meaning and structure to our lives; they are the
foundation for our families, friendships, workplace hierarchies, sexual contacts, and loving relationships. They impact our health and well-being, and
teach us about the cultures we live in. Human social neuroendocrinology
is the study of these types of social relationships, using a hormonal lens.
Social neuroendocrinology provides fascinating insights into the ways that
hormones influence our social relationships and, in addition, how our social
relationships affect our hormones. But, social neuroendocrinology is not just
about biology. It also sheds light on cultural processes and pays attention to
social experiences. This interactionist lens contributes to an ongoing reshaping of knowledge that incorporates both nature and nurture, biology and
culture, evolution and social construction.
We focus specifically on two kinds of social relationships in this article: (i)
adult-infant interactions such as those between parents and children and (ii)
adult partnering, such as pair bonds or romantic/sexual relationships. Many
aspects of our social relationships are unique to humans, whereas some are

Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.

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shared with other animals ranging from birds to rodents to nonhuman primates, and more. Those features common across species allow scientists to
study the evolved neurobiological systems that may be a common denominator in social relationships, albeit with attention to the uniqueness of each
species and taxa.
Social neuroendocrine perspectives on relationships draw on a number
of theoretical foundations. One of these was advanced by Niko Tinbergen
in the early 1960s. Tinbergen outlined how questions in biology can be
answered via four complementary levels of analysis: phylogeny (evolutionary history), function (adaptive explanations), mechanism (physiological
causal processes), and ontogeny (development; changes across the lifespan).
When we ask why an association between hormones and social relationships
exists, we are asking an ultimate question that is answered via research on
phylogeny and function. When we ask how this association exists, we are
asking a proximate question that is answered via research on mechanism and
development.
Another important theoretical foundation for social neuroendocrinology is
attachment theory, associated with John Bowlby and Mary Ainsworth. Here,
the notion is that humans are born with the goal of forming social bonds
with parental figures, because these are adaptive in promoting child survival.
Attachment is thought to drive much of social motivation and influences
other close social bonds. And, it means that social relationships of various
kinds are thought to share common features and even hormonal systems
with parent-infant bonds.
A third foundation for social neuroendocrinology is based on scientific
and agricultural experimentation with hormones. This is largely understood
to have originated in the nineteenth century with Arnold Berthold, who
transplanted testes from one species to another. However, recognition
that something in the body could influence social relationships has a
deep history, with castration of humans and other animals a longstanding
practice. Insights into what this “something” might be, however, arrived in
the twentieth century with the identification of steroid hormones such as
testosterone (secreted mainly from the testes or ovaries). This fostered the
development of behavioral neuroendocrinology; the study of hormones and
a broad range of behaviors.
Social neuroendocrinologists are largely interested in steroid hormones
and peptide hormones, which have pleiotropic—or multiple—functions that
are not limited to social relationships. Steroids are released from hormonal
glands and bind to hormone receptors located throughout the body and
brain. Androgens (e.g., testosterone), estrogens (e.g., estradiol), and glucocorticoids (e.g., cortisol) are the steroid hormone groups largely studied in
social neuroendocrinology. A mistaken belief is that androgens exist in men

Social Neuroendocrine Approaches to Relationships

3

and estrogens in women; in fact, both groups of hormones are functional
and present in women and men. Peptides are released from the pituitary
gland in the brain, and bind to specific receptors located throughout the
body and brain. Oxytocin, prolactin, and vasopressin are important peptide
hormones that, within social neuroendocrinology, are largely studied in
relation to attachment.
Hormones are actually released in response to signals from the brain. The
brain’s hypothalamus sends releasing signals to hormonal glands based on
an integrated mix of incoming messages from the rest of the brain, reflecting
the social environment, and actual hormone levels in the body. That’s one reason why social neuroendocrinology is interactionist, that is, that hormones
respond to internal (in the body) and external (e.g., social) phenomena.
Social neuroendocrinology uses a broad set of methods to assess how hormones and social relationships are associated. For example, some scientists
conduct experiments to determine effects of hormone on behavior. Others
experimentally examine how social behavior affects hormones. Still others
use correlational studies, group differences, or other neuroscience techniques
such as genetics or neuroimaging. Research might occur in the laboratory
or in the field. At its core, social neuroendocrinology is an interdisciplinary
endeavor that draws on perspectives from multiple fields. It provides important insights about hormones and social relationships, and the evolutionary
and cultural context in which our social relationships develop.
FOUNDATIONAL RESEARCH
One of the most important insights from social neuroendocrinology is that
social relationships can profoundly influence not only whether we feel loved
or supported, but also can reshape our very biologies. For example, rat
mothers engage in a variety of maternal behaviors, including pup licking,
that differ in frequency. As scientists have found, pups who were maternally
licked more frequently had different DNA methylation patterns compared
to low-licked pups, leading to epigenetic alterations of the glucocorticoid
receptor and impacting stress physiology.
Although parents can exert such strong effects on offspring, infants can
actually affect their caregivers as well. Studies have shown that attachment
behaviors (e.g., close touch, warm support) increase oxytocin and decrease
cortisol in both parents and children. This is thought to occur because the
physiology of caregiving seems to “borrow” from evolutionary systems that
underlie reproductive processes. For example, peptides such as oxytocin and
prolactin underlie lactation and birth, but also are implicated in attachment.
Estrogens and progesterone are intrinsic to ovulation and pregnancy, and
ratios between them seem important to maternal feelings during and after

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pregnancy. Of course, pregnancy, birth, breastfeeding, and the postpartum
are not merely hormonal or reproductive events themselves; they are also
social experiences. However, research on breastfeeding suggests that it has
hormonally mediated benefits for mothers in addition to nutritional and
attachment benefits for children: it increases and/or decreases cortisol and
stress responsivity in ways that seem to reduce stress and facilitate bonding.
There has been an explosion of interest into how peptides might mediate
attachment between parents and infants. In part, this is based on research
with species that, such as humans, develop close social bonds. The most
well-known model species is the prairie vole, that forms close parental and
pair bonds. In comparison to the closely related montane vole, prairie voles
show higher density of peptide receptors that have been experimentally
shown to support bonding behavior. Although social bonds do not work in
the same way across all species or contexts, and also do not necessarily rely
on the same neurobiological substrates, this research on social bonds has
been pivotal for human studies. Indeed, Sue Carter published a landmark
paper in the field that turned “love” into a respectable topic for neuroscience.
What does research with humans show? Prolactin actually increases in
response to infant stimuli in pregnant women, even before they have
children. After birth, mothers and fathers show bigger oxytocin increases
if they had more affectionate or stimulatory contact. And, higher oxytocin
seems to be related to more sensitive caregiving in women and men. Indeed,
parents with high levels of certain peptides seem to engage with their infants
in ways that reflect more synchrony, or matching of play styles or affect.
Still more research suggests that mothers with higher oxytocin responses to
infants are also more sensitive to affective and physical phenomena.
The above research demonstrates how individual differences in peptide
levels or responses are associated with differences in attachment-related
behaviors. Research has also demonstrated that administration of peptides
may have similar effects. Intranasal oxytocin administration to fathers seems
to have small effects on paternal behaviors with toddlers, like decreases
in hostility. This research is still somewhat controversial, however, as
many scientists question whether intranasal peptide administration can
actually affect the brain because of the blood brain barrier. What about
the infants? Research has suggested that oxytocin administration to parents
increases a set of behaviors that are known to support parent-infant bonds,
and—also—increase oxytocin and engagement in the infants themselves.
Conversely, socially-deprived children who were orphaned and subsequently adopted into caring families exhibited alterations in their oxytocin
and vasopressin systems.
Cortisol is better known as a stress hormone, but its function is actually more
broad, relating to activation and arousal in general. Interestingly, peptides

Social Neuroendocrine Approaches to Relationships

5

seem to dampen cortisol release. Cortisol is related to intimacy in interesting ways. For example, high cortisol has been linked to lower engagement
in attachment behaviors. But, high cortisol early in the postpartum is actually
associated with more attentive maternal behavior. This makes sense: it would
be adaptive, on hearing an infant shriek, to feel a sense of activation rather
than relaxation (at least for the infant!). Accordingly, whether cortisol’s association with caregiving is more or less valuable may depend on the given
caregiving culture and situation.
Although infant interactions affect parental hormones, parents also seem
to differ hormonally from nonparents in a variety of ways. For example,
some evidence shows that fathers and mothers have lower testosterone than
nonparents. This is largely interpreted via the “challenge hypothesis,” which
predicts that high testosterone should be linked with challenge and mating,
while low testosterone should be linked to parenting. Although developed
with birds, it has been extended to a number of species, including humans.
Fathers also differ hormonally from nonfathers in a variety of ways. In several other nonhuman mammals, such as common marmosets, fathers have
been found to have higher prolactin levels. A study of Filipino men found
that fathers had higher prolactin levels than nonfathers, the first time that
had been shown in humans.
The challenge hypothesis is also used to make sense of the ways in which
testosterone is linked to adult social bonds, like romantic/sexual relationships. Research from a number of labs has demonstrated that single, heterosexual men and women have higher testosterone than their partnered counterparts. This partnering can be marriage, cohabitation, or even long-term
relationships, and classic research first demonstrated the phenomenon using
participants from the army or air force, including a transient increase around
divorce in men. There is also evidence that cortisol levels are high in couples newly in love, highlighting further that “stress” reflects perturbations of
homeostasis even in positive situations.
Hormones are often fingered as the cause of lust, love, and other related
phenomena. It would be an exaggeration to claim a large role for them in
humans, but scientists have demonstrated fascinating if modest associations between hormones and the phenomena that underlie romantic and
sexual relationships. Research links peptides with phenomena like trust or
closeness that underlie pair bonds. Because many of the same phenomena
underlie pair bonds and parent-infant bonds, scientists have been excited
about findings that demonstrate overlapping neural substrates involved in
both. For example, viewing pictures of a beloved partner and a loved infant
results in neural activation in divergent areas but also some overlapping
ones that are known to be dense in oxytocin and vasopressin receptors. Thus, hormonal systems related to reproduction seem to have been

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

“borrowed” for parent-infant bonds, and also for pair bonds. As examples,
a number of studies identify links between the oxytocin system and aspects
of pair bonds. Women and men reporting higher marital quality had higher
blood oxytocin levels than individuals reporting lower marital quality,
and oxytocin increased with warm partner contact. Oxytocin levels are
higher in new lovers relative to singles. And, showing causal links between
oxytocin and pair bonds, the administration of intranasal oxytocin positively
impacted partner interactions during a standardized marital discussion. Of
course, pair bonds are characterized by more than just bonding—sexuality
plays an important role too.
Orgasm and sexual behavior also increases oxytocin and other peptides.
Perhaps this relates to oxytocin’s role in mediating muscular contractions in
parity-related events, like uterine contractions for birth and milk ejection in
breastfeeding. Other hormones are also implicated. Estradiol, an estrogen,
seems to be correlated with affiliative phenomena, like sexuality.
Testosterone is another hormone that is often linked with sexuality. Indeed,
it does increase following exposure to sexual stimuli, engagement in sexual
activity, and even sexual thoughts. In fact, testosterone seems to respond to
sexuality more strongly than it influences sexuality in humans. For example,
researchers found that heterosexual men engaged in flirtatious behavior with
women had an increase in testosterone.
A separate line of research examines attraction to potential partners across
the menstrual cycle. The idea is that during fertile times of the menstrual
cycle, when estrogen and androgen levels rise, women may exhibit changes
in the characteristics they seek in a partner. In one review, women showed
increased attention to masculine faces and voices during their fertile menstrual phase. Other studies suggest that women’s sociosexual behavior can
also shift during fertile phases. The observation of these kinds of cycle-related
effects suggests they are subtle, and studies employ variable methodological rigor (e.g., definition of cycle phases, whether hormones are measured
or not).
There are a number of important findings from social neuroendocrinology
on relationships, ranging from romantic contacts to parent-infant bonds.
These have led to novel insights about the role of hormones in human social
connections. However, as researchers delve more deeply into these newly
discovered phenomena, sometimes well-accepted findings are turned on
their head even as others are more decisively confirmed.
CUTTING EDGE RESEARCH
Do fathers have lower testosterone than nonfathers? Does oxytocin promote
love? Do singles have higher testosterone than married folks? Do menstrual

Social Neuroendocrine Approaches to Relationships

7

shifts in psychology occur? Cutting edge research in social neuroendocrinology addresses the nitty-gritty details and truth-value of these claims. For
example, peptides are largely thought of as “prosocial,” meaning that they
are always “good” in relation to social bonds. But, researchers are finding
that empirical evidence is actually more complicated than the initial story
suggested. Thus, even though oxytocin is thought to promote social bonds,
it also seems to reflect a need for social bonds: women with self-reported
poorer relationship functioning have higher oxytocin than women who
are satisfied with their relationships. Evidence suggests that oxytocin may
amplify social affect. In this case, one could easily imagine how oxytocin
administration might amplify undesirable aspects of social bonds. Moreover, context is increasingly understood to matter. For example, oxytocin
administration lessens an overharsh grip strength in response to hearing
infant cries, but only among women who were not harshly disciplined
themselves as children.
Of course, context is not just background or mood states. It can also be
physiological, and behavioral genetics work in social neuroendocrinology
has demonstrated just this. For example, though oxytocin administration can
increase preference for infant faces, it does so only in individuals with a specific polymorphism on the gene that codes for oxytocin receptors. Differences
in the vasopressin 1a receptor have been associated with partner bonding
behaviors. However, those associations were only true of men.
Even hormones can be a context for each other, and scientists are increasingly attending to interactions between hormones and their implications for
social relationships. In one such framework, the steroid/peptide theory of
social bonds (S/P theory), peptides are related to social bonding phenomena,
including even negative behaviors that might be related. In contrast, testosterone is negatively associated with nurturant social bond phenomena, and
positively associated with competitive behaviors that are aimed at acquiring
or defending resources (that may include social or sexual bonds themselves!).
Another integrative theory—the Dual Hormone Hypothesis, has been used
around competition and is less used around social relationships, though is
promising. It predicts that testosterone is linked to social behaviors in ways
that are mediated by cortisol levels.
One perplexing finding in social neuroendocrinology has been that infant
cries increase testosterone and that testosterone can upregulate neural areas
involved in parental care, in contrast to most theoretical predictions. More
recent research has demonstrated that nurturant behaviors while hearing
infant cries does decrease testosterone, as predicted by the S/P theory.
Scientists are increasingly attending to the specificities of the behavior under
investigation, in ways that shed light on their associations with hormones.
For example, though parents sometimes have lower testosterone than

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

nonparents, they sometimes have higher testosterone. This may be because
some parenting involves nurturance and direct care, while some involves
competitive behaviors and indirect care. Research does suggest that parents
of younger children who are more involved in nurturant care are the ones
with lower testosterone.
Relationships, too, are linked to testosterone in more nuanced ways.
Marriage is likely a proxy at best for the underlying constructs related
to testosterone. Cross-cultural research has highlighted that partnering
is not the same world over, and sometimes even pair bonds involve the
possibility of new partners. In this way, research has shown that, whether
in a relationship or not, interest in new or more partners is associated
with higher testosterone in men, whereas presence of more partners or
more sexual behavior is associated with higher testosterone in women.
Indeed, one interesting outcome of this research has been the suggestion
that testosterone is linked to relationship status in women, but relationship
orientation in men. This body of research shows that relationships are diverse
and can involve commitment and/or extra-pair sexuality and that it is these
nuances that seem to clarify how specific kinds of relationships are linked to
hormones.
What about relational dynamics themselves? A variety of studies have
investigated links between cortisol and partner quality. Some studies test
whether patterns of cortisol concentrations across the day are related to
partnership factors; more partner intimacy was associated with lower cortisol profiles in a naturalistic study. Other studies led by Kiecolt-Glaser and
Glaser at The Ohio State University have entailed younger and older couples
reporting to a lab to engage in a standardized marital conflict discussion
session, testing effects of partner discussions on cortisol profiles. As an
example, the marital satisfaction reported by wives was inversely related
to their cortisol change across a marital discussion, with more satisfied
wives showing more rapid cortisol declines. In addition, a study noted
above observed that intranasal oxytocin decreased cortisol levels during
marital discussions, showing the relationships between oxytocin and stress
hormone reduction.
Though sexual desire is largely assumed to be clearly related to testosterone, research actually shows that desire itself is more complicated. For
example, studies have found that solitary sexual desire, or desire to masturbate, is positively correlated with testosterone in women, but not men,
whereas dyadic sexual desire, or desire to be sexual with another person,
is negatively correlated in women but not men. Social neuroendocrinology
helps to highlight what desire is actually about, as desire may reflect interest in intimacy, closeness, orgasm, sleep, and so on. It may be that desire for
intimacy maps onto lower testosterone, and desire for erotic pleasure maps

Social Neuroendocrine Approaches to Relationships

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onto higher testosterone. Interestingly, these results hold only for women.
Research on sexual desire and testosterone in healthy men shows no significant correlation between testosterone and desire in healthy men despite
longstanding assumptions to the contrary.
The postpartum is often a time for parent-infant bonding, but this still
occurs—for many people—within the context of an adult relationship like
marriage. Indeed, changes in relationships are a hallmark of the postpartum
for most parents. There is some belief that decreases in partnered sexual
behavior or sexual desire may map onto the hormonal processes associated
with parity. There is also evidence that social changes associated with the
new parenting roles, relationship structures, and having a new baby are
related to postpartum sexuality in both mothers and coparents. And, though
researchers have generally focused on low sexual desire and infrequent
sexual activity during this time, evidence suggests that many birth mothers
are actually engaging in a variety of sexual behaviors at this time. What
might be most interesting about postpartum sexuality, however, is how
similarly birth mothers and their coparents experience it. This suggests that
hormones, if involved, may be reacting to the social changes around birth
rather than the birth-specific reproductive events themselves.
Recent cutting edge research in social neuroendocrinology had tended to
add more “grey” to early “black-and-white” findings, adding nuance and
contextual considerations. In addition, this body of literature is attending
more closely to the details of the social phenomena under study to get to the
core of what it is about relationships, desire, or parenting, as some examples,
that is reliably linked to hormones. Finally, the most up-to-date research
takes a more skeptical stance, not undermining that hormones and social
behaviors are meaningfully and interestingly connected, but attending to a
fuller realm of possible links including null associations, moderation, and
counter-expected associations.
KEY ISSUES FOR FUTURE RESEARCH
Social neuroendocrine approaches to relationships are so new that a number
of key issues have only recently been identified. For example, the focus
on a limited set of social relationships (like marriage, parent–child bonds,
etc.) limits our understanding of all social relationships. Attending to relationships like friendships, grandparenting, adoptive- and step-parenting,
nonparental childcare, sibling care, mentoring, and even human-pet interactions will likely be informative. And, though research has often focused
on hormonal mediation of the positives of human social relationships, like
love, intimacy, and attachment, there are a number of “negatives” that
merit investigation too. For example, how might social neuroendocrinology

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help us understand child neglect, partner abuse, rape, or intrafamilial
aggression? Moreover, participants in social neuroendocrinology tend to be
adults, or a focus on adult–infant bonds. It remains to be seen whether the
same hormonal processes are tied to caregiving of older children, much less
teenagers or adult offspring.
There are a number of additional axes along which differences can and
likely will matter. For example, the majority of social neuroendocrinology,
especially about hormones and parent-infant bonds, has been conducted
with “WEIRD” populations. But individuals who are white, educated, industrialized, rich, and democratic make up a very narrow slice of human diversity.
Basic research that presumes “good” or “bad” aspects of social bonding will
need to reconcile these notions with parenting across cultures (and within
Western nations) that have different norms. But, relatedly, research that
more explicitly addresses the applied implications of social neuroendocrine
studies of social relationships will also be important. This will require
acknowledging that social neuroendocrinology has sometimes erred on
the side of focusing on universal generalities rather than local specificities,
because applications are potential solutions to particular problems that are
generally culture-bound. Addressing both cultural diversity and cultural
specificity will thus be an important next step in both exploring the basic
social neuroendocrinology of relationships and its exciting applied potential.
Both basic and applied research require attending to cause and effect.
Currently, perhaps because of the scientism inherent in incorporating hormonal and biological measures into research, scientists are largely studying
how hormones might influence social bonds or using that arguable biologically deterministic perspective. This lens is but one approach, however,
because biology need not be biologically deterministic or unidirectional.
Other exciting cutting-edge biological approaches include epigenetics (how
experiences modify genetic processes), social determinants of health, and
phenotypic plasticity (e.g., how experience shapes the brain and body).
For social neuroendocrinology, attending to these perspectives include
addressing how social bonding processes affect hormones, and interactionist questions of how social relationships and hormones mutually influence
each other. Moreover, hormone administration studies have been conducted
with a generally narrow frame. For example, work on intranasal oxytocin
or vasopressin sprays is interesting, but it is still far from clear whether
they have central actions. And, because scientists largely focus on only their
prosocial effects, “side” effects and undesirable outcomes remain largely
unstudied despite concerning research pointing to them.
The focus on WEIRD populations has not been as prevalent in research on
testosterone and partnering, perhaps because this field includes researchers
from biological anthropology as well as psychology and neuroscience. This

Social Neuroendocrine Approaches to Relationships

11

body of research demonstrates the importance and value of attention to culturally diverse forms of partnering. In addition, by incorporating individuals
who are lesbian, gay, bisexual, polyamorous, and in open relationships, it
highlights how sexual diversity, in addition to cultural diversity, is illuminating. Even WEIRD populations are not only single or married, and relational
approaches may be diverse. In fact, one could amend the term to WHEIRD,
with “H” signifying heterosexual. The majority of research focuses on one
specific kind of gendered pair bonds, but sexualities are broader than this.
Attention to bisexuality, same-sex sexuality, and even sexual fluidity will be
important. A growing movement of individuals to define an asexual identity
highlights diverse relational and sexual bonds, which will be important for
social neuroendocrinology to include. For example, demi-sexuals are individuals who experience sexual attraction to a person only after romantic connections. How might this map onto social neuroendocrine systems for social
and/or sexual connections? A key challenge for social neuroendocrinology
will be to attend to diversity rather than difference. For example, instead of
asking whether gay and straight men show similar neural responses to loved
ones, the field might ask how gendered sexuality is implicated among other
variables, and alongside socialization factors, in hormone-behavior associations. Indeed, socialization and social constructs remain understudied but
powerful lenses for social neuroendocrinology.
For those interested in understanding developmental trajectories, what is
strongly needed is a life course or life history perspective. For example, do
early parent-infant bonds have effects on hormonal systems in ways that
influence adult social bonds? Puberty is also increasingly recognized as a
period of hormonal plasticity, but remains understudied in human social
neuroendocrinology. Indeed, cause and effect remains to be hammered out
in a number of contexts. Longitudinal studies tend to be designed to answer
other questions, and often end up answering part but not all of this question.
Accordingly, life course studies would be informative.
The field would also benefit from increased comparative attention. At
present, there is already a large influence of nonhuman animal research on
human research. This makes sense, because there are a number of questions
that can only be answered with animal models. However, a comparative
approach requires attending to species-specificities. Accordingly, research
from one species can only inform understandings of another—it cannot be
immediately generalized. Already, there is clear evidence that the hormonal
and neurobiological substrates of social bonding are not the same across
species. For example, oxytocin and vasopressin receptor density underlie
differences between monogamous and multisexual voles, but not birds or
even other rodents. If the same hormonal processes do not underlie social
bonds among different rodents, it is obviously difficult to translate them

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

to humans. At the same time, understandings from other species may help
shed light on underlying processes, and are sometimes absent when they
could be helpful. For example, work with nonhuman primates shows both
similarities and differences in the hormonal mechanisms associated with
paternal care compared with humans.
Also missing is neural work that is conducted alongside hormonal studies. Research on neural imaging has largely relied on imaging those areas
already known to be implicated in social bonds—in other species. But, given
that these areas may not translate even to other rodents, there may be a host of
neural structures relevant in humans that current science is missing. Future
research will need to incorporate multiple methods into the same studies,
for example examining hormonal and neural changes to social bond stimuli alongside each other. Coupled with a life course approach, this could be
very powerful. For example, how might neural and hormonal responses to
infant stimuli differ after extensive caretaking experience or social bonding,
compared to controls?
Methodological issues abound in social neuroendocrinology, and need
attention for the field to move forward in rigorous ways. For example,
cortisol and testosterone exhibit large diurnal variation but it is unclear
how dynamic other socially relevant hormones might be. There are also
sampling issues, including how closely tied measures from fluids like
saliva, blood, urine, or cerebrospinal fluid might be and how well each
represents central (i.e., brain) activity. Some methodological reviews have
addressed these concerns but are constrained by what limited methodological research exists. Thus, a key task for social neuroendocrinologists will
be to incorporate methodological questions and sophistication into their
research.
The future of social neuroendocrinology is bright. As more researchers from
a variety of disciplines and sub-disciplines understand the value and ease
of incorporating hormone measures into their work, social neuroendocrine
work on relationships will continue to grow and become integrated into other
fields. Work is becoming increasingly sophisticated and nuanced, leading to
insights about hormones themselves, social relationships, evolutionary considerations, proximate mechanisms, and potential applications to real-world
problems.
FURTHER READING
Adkins-Regan, E. (2005). Hormones and animal social behavior. Princeton, NJ: Princeton
University Press.
Bartz, J. A., Zaki, J., Bolger, N., & Ochsner, K. N. (2011). Social effects of oxytocin in
humans: Context and person matter. Trends in Cognitive Sciences, 15(7), 301–309.

Social Neuroendocrine Approaches to Relationships

13

Carter, C. S. (1998). Neuroendocrine perspectives on social attachment and love. Psychoneuroendocrinology, 23(8), 779–818. doi:10.1016/S0306-4530(98)00055-9
Churchland, P. S., & Winkielman, P. (2012). Modulating social behavior with oxytocin: How does it work? What does it mean? Hormones and Behavior, 61(3),
392–399.
Ellison, P. T., & Gray, P. B. (2009). Endocrinology of social relationships. Cambridge, MA:
Harvard University Press.
Goodson, J. L. (2013). Deconstructing sociality, social evolution and relevant nonapeptide functions. Psychoneuroendocrinology, 48(4), 465–478.
Granger, D. A., Kivlighan, K. T., Fortunato, C., Harmon, A. G., Hibel, L. C., Schwartz,
E. B., & Whembolua, G. L. (2007). Integration of salivary biomarkers into developmental and behaviorally-oriented research: Problems and solutions for collecting specimens. Physiology & Behavior, 92(4), 583–590. doi:10.1016/j.physbeh.
2007.05.004
Muehlebein, M. P., & Flinn, M. V. (2011). Patterns and processes of human life history evolution. In T. Flatt & A. Heyland (Eds.), Oxford Handbook of Life History (pp.
153–168). Oxford, England: Oxford University Press.
Nelson, R. J. (2011). An introduction to behavioral endocrinology (4th ed.). Sunderland,
MA: Sinauer Associates.
Oliveira, R. F. (2009). Social behavior in context: Hormonal modulation of behavioral
plasticity and social competence. Integrative and Comparative Biology, 49, 423–440.
Rilling, J. K. (2013). The neural and hormonal bases of human parental care. Neuropsychologia, 51(4), 731–747.
Robles, T. F., & Kiecolt-Glaser, J. K. (2003). The physiology of marriage: Pathways to
health. Physiology & Behavior, 79(3), 409–416.
Taylor, S. E. (2006). Tend and befriend: Biobehavioral bases of affiliation under
stress. Current Directions in Psychological Science, 15(6), 273–277. doi:10.1111/j.14678721.2006.00451.x
Tinbergen, N. (1963). On aims and methods of ethology. Ethology, 20, 410–433.
van Anders, S. M. (2013). Beyond masculinity: Testosterone, gender/sex, and human
social behavior in a comparative context. Frontiers in Neuroendocrinology, 34,
198–210.
van Anders, S. M., Goldey, K. L., & Kuo, P. X. (2011). The steroid/peptide theory of
social bonds: Integrating testosterone and peptide responses for classifying social
behavioral contexts. Psychoneuroendocrinology, 36(9), 1265–1275.
Weaver, I. C. G., Cervoni, N., Champagne, F. A., D’Alessio, A. C., Sharma, S., Seckl,
J. R., … , Meaney, M. J. (2004). Epigenetic programming by maternal behavior.
Nature Neuroscience, 7(8), 847–854.
Wingfield, J. C., Hegner, R. E., Dufty, A. M., Jr., & Ball, G. F. (1990). The “challenge
hypothesis”: Theoretical implications for patterns of testosterone secretion, mating systems, and breeding strategies. American Naturalist, 136, 829–846.
Young, K. A., Gobrogge, K. L., Liu, Y., & Wang, Z. (2011). The neurobiology of
pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology, 32(1), 53–69.

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

SARI M. van ANDERS SHORT BIOGRAPHY
Sari M. van Anders, PhD, is an Assistant Professor of Psychology and
Women’s Studies at the University of Michigan, and affiliated with UM’s
programs in Neuroscience, Reproductive Sciences, Science, Technology, and
Society, and the Biosocial Methods Collaborative. In the Social Neuroendocrinology Lab, Dr. van Anders studies hormones and social behaviors
in social context, paying special attention to sexuality, intimacy, and nurturance. Dr. van Anders’ PhD is in behavioral neuroscience, earned at
Simon Fraser University in Canada, in 2007. With over 50 publications in
social neuroendocrinology, health, gender/sex, and sexual diversity, Dr. van
Anders focuses on feminist and inclusive research practices. Dr. van Anders
is the Editor-Elect of the Annual Review of Sex Research and, in 2013, Dr.
van Anders received the Janet Taylor Spence Award for Transformative
Early Career Contributions from the Association for Psychological Science.
PETER B. GRAY SHORT BIOGRAPHY
Peter B. Gray, PhD, takes an integrative evolutionary perspective of
human reproduction. This means drawing on comparative nonhuman
findings, cross-cultural research, neuroendocrine mechanisms, and life
history theory to make sense of our behavior. He most thinks about how
an evolutionary perspective makes sense of human sexuality, fatherhood,
and even pet-keeping. He earned BA degrees in Anthropology and Geography/Environmental Studies at UCLA and a PhD in Biological Anthropology
in 2003 from Harvard University, also undertaking postdoctoral research
in Clinical Endocrinology. He has coedited (2009) “Endocrinology of
Social Relationships,” and coauthored “Fatherhood: Evolution and Human
Paternal Behavior” and “Evolution and Human Sexual Behavior,” all with
Harvard University Press.

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