Emerging Trends in The Social and Behavioral Sciences

Motherhood

Item

Title

Motherhood

Author

Hinde, Katie

Research Area

Social Interactions

Topic

Family Relationships

Abstract

Motherhood is fundamentally the state of being a mother. In mammals this manifests as behaviorally nurturing and physiologically nourishing one's young. The state of motherhood requires substantial and dramatic changes in the mother's behavior, brain, and body. Moreover among humans, motherhood occurs within a familial, socioeconomic, and cultural context. Among many animals, to become a mother marks the transition to a new stage of life, from a period dedicated to growth and development to a period of sexual maturity and productivity. Considering trade‐offs within and across the stages of the life course, known as life history theory, is essential to understand motherhood. Moreover, the interests of the mother and the infant overlap, but are not identical, leading to conflicts of interest. Here we will consider established and emerging topics of investigation into motherhood—from the neuron to the society—and directions for the future.

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extracted text

Motherhood
KATIE HINDE

Abstract
Motherhood is fundamentally the state of being a mother. In mammals this manifests as behaviorally nurturing and physiologically nourishing one’s young. The state
of motherhood requires substantial and dramatic changes in the mother’s behavior,
brain, and body. Moreover among humans, motherhood occurs within a familial,
socioeconomic, and cultural context. Among many animals, to become a mother
marks the transition to a new stage of life, from a period dedicated to growth and
development to a period of sexual maturity and productivity. Considering trade-offs
within and across the stages of the life course, known as life history theory, is essential to understand motherhood. Moreover, the interests of the mother and the infant
overlap, but are not identical, leading to conflicts of interest. Here we will consider
established and emerging topics of investigation into motherhood—from the neuron
to the society—and directions for the future.

INTRODUCTION
In 1952, John Bowlby and his colleague James Robertson presented a short
film entitled “A Two-Year-Old Goes to Hospital.” Over the course of an
eight day hospital stay, the infant deteriorated in the absence of maternal
care despite nutritional and medical support. This dramatic interruption
of the mother-infant dyad served as a window into the infant’s psychological processes in light of separation from the mother. From expanded
studies by Bowlby, cross-cultural investigations of mothers and infants
by Mary Ainsworth, and rhesus macaque experiments by Harry Harlow,
Steve Suomi, and colleagues, the mid-twentieth century laid a foundation
for Attachment Theory and established a framework for evaluating the
mother-infant dynamic, the role of the mother, and the consequences for
infants. Maternal behavioral care was demonstrated to be an important
contribution to species-typical behavioral development and physiological
regulation. This expanding research into the importance of maternal love
was a crucial repudiation of the conventional “wisdom” of regimented
infant care recommended by many prominent physicians between WWI
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

and WWII. Prior to these empirical studies, mothers were cautioned against
excessive affection—such as cuddling and soothing—directed toward the
infant (Lewis, 1982).
Notably, studies of mothers were, and remain to this day, mostly
infant-centered, that is to say, predominantly designed to investigate infant
outcomes. Progeny are the principle currency of natural selection, attracting
the interests of evolutionary biologists and behavioral ecologists. Piagetian
psychologists, Batesian linguists, and Barkerian DOHaDians1 are motivated
to understand how early environment and experiences influence cognitive
development, language acquisition, and physiological function into childhood and adulthood. Parents, clinicians, and public health advocates are
particularly motivated to optimize infant outcomes.
However, mothers, and their experience of motherhood, are more than
merely inputs into infant developmental trajectories. Depending on the
social, behavioral, or life science lens through which motherhood is assessed,
one can approach it as a state, a stage, and a construct. Fundamentally, motherhood is the state of behaviorally caring for young—after either producing
one’s own biological young as is typical, or occasionally in the case of
humans, through adoption of a nonbiological infant or child. Among many
animals, to become a mother marks the transition to a new stage of life, from
a period dedicated to growth and development to a period of sexual maturity and productivity. Considering trade-offs within and across the stages
of the life course, known as life history theory, is essential to understanding
motherhood. Across species, motherhood involves substantial changes in
behavior—not only in direct care of the infant, but also indirectly by changed
interactions with other individuals. Motherhood precipitates a cascade of
neurobiological and physiological changes that mediate infant care and
nourishment as well as transitions to the next reproductive effort. Among
humans, motherhood is also a feature of personal identity—a construct of
self, as well as a cultural construct. Here we will explore recent studies that
provide new information about motherhood and identify future directions
that enhance the translational utility of scholarly studies of motherhood.
EVOLUTIONARY CONTEXT
LIFE HISTORY THEORY
Before evaluating maternal behavioral care and physiological investment,
we must consider life history theory and parent-offspring conflict. All
biological organisms face trade-offs for allocating energy among competing
1. A reference to key scholars influencing their disciplines: cognition and Jean Piaget, linguistics and
Elizabeth Bates and Developmental Origins of Health and Disease and David P. Barker.

Motherhood

3

processes. Drawing a parallel with Economics 101 and the “guns versus
butter model,” capital is finite and money supporting the manufacture
of one commodity is no longer available for another commodity. Such
is energy for the biological organism; a calorie can only be burned once.
Organisms have finite resources, such as energy, that are allocated to somatic
maintenance, development, and reproduction (Stearns, 1992). For examples,
among mammals, maintenance includes the physiological processes of
immune function, digestion, and endothermic thermoregulation. Development includes growth, neurogenesis, and skeletal ossification. Reproduction
requires mating, gametogenesis, and for females—pregnancy and lactation.
Mobilization of stored fat on the mother’s body for milk synthesis is fat
that is no longer available for the mother’s thermoregulation or future
reproduction. She must recover those stores before resuming estrus and the
next reproductive event (Valeggia & Ellison, 2009). As such, motherhood
occurs within a framework of necessary trade-offs. Natural selection favored
traits that produced adaptations that underlie contingencies for allocating
energy among behavioral activity and physiological processes to maximize
lifetime reproductive success (Clutton-Brock, 1991). Reproductive success
is measured as the number of offspring produced that reach reproductive
maturity across an entire reproductive career. As a result of these many
factors and constraints, mammalian mothers are expected to vary their
effort and investment in individual offspring in relation to the mother’s own
condition, the offspring’s condition, and the time point in her reproductive
career (Clutton-Brock, 1991). The many moving parts of the mother-infant
dynamic complicate greatly studies of motherhood. This is particularly true
when one considers that the mother and infant may have, to some extent,
divergent interests when they interact.
PARENT-OFFSPRING CONFLICT
Natural selection has not only acted on adaptations in mothers. The infant
plays an important role within the mother-infant dynamic. Just as mothers face trade-offs between maintenance and reproduction, so infants face
trade-offs between maintenance and growth (Stearns, 1992). Moreover the
interests of the infant and the mother are not perfectly aligned. Mothers are
equally related to each of their offspring, as offspring inherit 50% of their
genetic material, on average, from their mother. All else being equal, mothers
are predicted to allocate resources equally among their offspring. But infants
are 100% related to themselves, only 50% related to their mother and only
25–50% related to their mother’s other offspring, depending on whether their
share a father in addition to sharing a mother. Invoking Hamilton’s rule,
Trivers (1974) argued that this difference between self and relative would

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

generate parent-offspring conflict of interest over the amount and duration
of investment from the mother and adaptations in offspring to extract greater
investment from the mother. The mother-infant dynamic is therefore shaped
by an essential tension as the mother and offspring negotiate behavioral care
and physiological investment between their respective optima (Hinde, 2014).
Negotiation of these divergent interests are further complicated as within the
infant, genes of paternal origin and genes of maternal origin are also potentially in conflict (Haig, 2014). The complexity and nuance embedded within
the “symbiosis of parent–offspring interactions” are therefore a particularly
challenging area of research in the social and behavioral sciences (Rosenblum
& Moltz, 1983).
THE BEHAVIORAL BIOLOGY OF MOTHERHOOD
MATERNAL BEHAVIOR
A suite of behaviors are generally associated with motherhood and can
include protection, vigilance, nourishment, transporting, physical comforting of the young and in socially complex species, mothers may intervene on
their offspring’s behalf during social encounters. The form of these behaviors
will vary across species—for example, nourishment can take the form of
mother’s milk or provisioned foods. Physical comforting can be licking,
grooming, and huddling. Mother–infant interactions have been one of the
most prevalent and enduring research areas in anthropology, psychology,
and primatology. Primate and rodent models have been particularly useful
in understanding maternal behavior (Champagne, 2014; Champagne &
Meaney, 2001; Dettmer, Suomi, & Hinde, 2014; Phillips et al., 2014). From
these studies, we have a deep appreciation that mothers display substantial
individual variation in their behavioral care of infants. In a diversity of
animal taxa, variation in maternal care has been associated with social
rank, social environment, ecological conditions, genetic predispositions, and
prior experience rearing young (Champagne & Meaney, 2001; Fairbanks,
1993; Fairbanks & Hinde, 2013; Hrdy, 2009; Maestripieri & Mateo, 2009;
Meaney, 2001). Long-term assessment of maternal care in free-ranging rhesus
macaques on Cayo Santiago showed that females had consistent “mothering
styles,” mother infant interactions of proximity, contact, and rejection
were consistent across age periods and between infants (Berman, 1990).
Cross-fostering experiments have been conducted with rhesus macaques at
Yerkes that demonstrate that maternal–infant interactions are genetically
coadapted (Maestripieri, 2004). More rejecting mothers produce infants that
are more inclined to make contact and vice versa (Maestripieri, 2004). In a

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series of landmark studies, Rosenblum and colleagues manipulated foraging demands on mothers to understand how it changed their behavioral
interactions with their infants and other monkeys in the social group. The
researchers created three foraging conditions; (i) high foraging demand
(HFD) 90–100 monkey biscuits were hidden in 1000 food holes (110% of
their normal diet), (ii) low foraging demand (LFD) 600 biscuits were hidden
in 1000 food holes, and (iii) variable foraging demand (VFD) in which food
was provided either the HFD or LFD condition on a 2-week cycle. The
VFD condition seemed to be psychologically demanding for mothers. These
mothers were less attentive to their infants, broke contact with their infant
significantly more frequently, and infants expended greater effort to reestablish contact than in the HFD or LFD groups. Among the adults in the VFD
condition, including mothers, there were more hierarchical interactions (e.g.,
aggression, displacement) and less grooming. These studies provide strong
evidence that unpredictable environmental conditions are particularly
difficult on mothers even though the foraging demands were intermediate
between the HFD and LFD. The variable aspect of the VFD condition was
more stressful and had a greater affect on maternal care than even the
condition in which foraging demands were always high (Rosenblum &
Andrews, 1994; Rosenblum & Paully, 1984). This pioneering work continues
to this day, revealing that individuals reared under VFD conditions have
deficits in adulthood and transmit variable foraging demand consequences
across generations (Coplan et al., 2001; Coplan et al., 2006; Kinnally et al.,
2013). Increasingly, studies of maternal behavior have expanded beyond
ethology to understand the neurobiology and physiology of motherhood
(Clancy, Hinde, & Rutherford, 2013), or rather the maternal brain and the
maternal body.
THE MATERNAL BRAIN
The mother-infant bond is established shortly after birth via neurobiological
mechanisms. The dopaminergic and oxytocinergic neuroendocrine pathways underlie the mother-infant bond—neurobiologically motivating and
rewarding mothers for maternal care. Naturally occurring variation in the
production, reception, and distribution of dopamine and oxytocin within the
maternal brain, among other neurotransmitters, can contribute to variation
in maternal responsivity, attachment, and behavioral care (Carter, Lederhendler, & Kirkpatrick, 1999; Feldman, Gordon, Schneiderman, Weisman,
& Zagoory-Sharon, 2010; Insel & Young, 2001; Saltzman & Maestripieri,
2011; Strathearn, Fonagy, Amico, & Montague, 2009). Most research into
the maternal brain has occurred in the rodent model because of ethical,
experimental, and logistical considerations. Much less is understood in

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

the primate brain, including humans, although new imaging technologies
are affording researchers more options for investigating brain changes as a
function of motherhood. In human mothers, the brain undergoes morphological changes in the weeks and months after giving birth. Specifically, the
amount of grey matter, rich with neuronal cell bodies, increases in regions
of the brain that are critical for sensory perception, emotion processing, and
motivation (Kim et al., 2010). These morphological changes are consistent
with functional imaging showing increased oxygen utilization and glucose
uptake in these same regions during the early months of motherhood
(reviewed in Kim et al., 2010). Most intriguingly, mothers who self-reported
the most positive thoughts about their baby at the outset of the study
showed the greatest increases in grey matter months later (Kim et al., 2010).
This result suggests that perceptions of motherhood and mother-infant
dynamics may positively feedback, enhancing maternal behavior, but this
remains speculative in the absence of more data. Higher circulating oxytocin
in human mothers has been associated with increased maternal bonding
behaviors, such as gazing at, checking on, and speaking to the infant, as well
as affectionately touching and positive affect regarding the infant (Feldman,
Weller, Zagoory-Sharon, & Levine, 2007; Gordon, Zagoory-Sharon, Leckman, & Feldman, 2010). Although not directly measuring the maternal brain,
they still provide insight into the physiology of motherhood. Moreover,
many of the hormones that mediate behavioral care in the brain also exert
important peripheral effects that are critical for mothers during lactation.
Particularly important, prolactin stimulates milk production while oxytocin
triggers milk letdown for transfer to the infant (Lincoln, 1983) and among
mammals, milk is a particular marker of motherhood.
THE MATERNAL BODY
The synthesis of milk by mammary glands is the defining characteristic of
our mammalian class. Unfortunately, we still know relatively little about
postnatal maternal physiological investment. For example, much more
research effort has been dedicated to understanding pregnancy than aspects
of lactation, particularly breast milk composition (Figure 1). Mother’s milk
consists of hundreds, possibly thousands of bioactive constituents, including
numerous fats, proteins, sugars, vitamins, minerals, immunofactors, and
hormones as well as water that hydrates the neonate (Hinde & Milligan, 2011;
Neville et al., 2012). How mothers pay the costs of lactation vary according to
life history theory. Mothers energetically support lactation via a diversity of
tactics and strategies that vary across individuals and species. Lactation can
be supported by mobilizing body reserves (Oftedal, 2000); basically mothers
dissolve parts of themselves to feed their young. Others rely to a greater

Motherhood

Number of articles x 1000

800

7

769.4

700
600
500
400
WHAT?!

300
200
72.7

100

32.6

0
Pregnancy

Lactation

Breast milk

2.3
Breast milk
composition

Figure 1 The number of articles returned as a result of keyword searches in
PubMed, a database maintained by the United States National Library of Medicine
(NLM) at the National Institutes of Health. Key word search conducted on June 1,
2014.

extent on dietary intake to sustain lactation. Conceptually these approaches
can be characterized as “capital” and “income” breeding (Jönsson, 1997).
However in practice most species exhibit multiple tactics to sustain lactation,
relying on the mobilization of maternal reserves and dietary intake, as well
as behavioral compensation and metabolic efficiencies (Gittleman & Thompson, 1988; Speakman, 2008). The tactics utilized to sustain lactation can therefore influence interbirth interval and consequently lifetime reproductive
success. In baboons, chimpanzees, and humans, weight loss from mobilizing
bodily reserves to sustain lactation, suppresses ovulation and subsequent
conception is contingent on maternal recovery (Emery Thompson, 2013).
Given that mothers face trade-offs and rely on different tactics during
lactation, substantial variation in milk synthesis is to be expected. Indeed a
growing body of literature evaluating mother’s milk from an evolutionary
perspective, demonstrates that mother’s milk varies across time, across
individuals, across populations, and across species (Hinde & Milligan,
2011; Neville et al. 2012; Oftedal & Iverson 1995; Skibiel, Downing, Orr, &
Hood, 2013). First-time mothers generally produce lower volumes of milk
during lactation than do experienced, multiparous females in humans,
monkeys, pinnipeds, rodents, and bovids (reviewed in Hinde, Carpenter,
Clay, & Bradford, 2014; Hinde, Power, & Oftedal, 2009). Maternal diet can
also predict milk composition (Hinde & Milligan, 2011; Milligan & Bazinet,
2008; Skibiel et al., 2013). Maternal parasite load is associated with lower
milk production in cows (Perri et al., 2011) and milk fat concentration in
rhesus monkeys (Hinde, 2007). Moreover, although mothers synthesize
milk, accumulating evidence suggests that sometimes milk differs between

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

sons and daughters in red deer, bank voles, cows, wallabies, rhesus monkeys, and humans (reviewed in Hinde et al., 2014). Some milk bioactives,
such as glucocorticoids, vary substantially among mothers (Grey, Davis,
Sandman, & Glynn, 2013) and has recently been shown to reflect maternal
life history (Hinde et al., 2014). Better knowledge of sources of variation,
especially for milk constituents linked to maternal condition can lead to
more personalized clinical recommendations for mothers and their infants.
Such knowledge has the potential to inform decisions about breast-feeding
initiation and duration, improve replacement and supplemental formula
compositions, and husbandry practices and nursery rearing of mammalian
young in research or agricultural settings.
Typically the public discourse on breastfeeding among WEIRD societies
[Western, educated, industrialized, rich, and democratic (Henrich, Heine,
& Norenzayan, 2010)] has remained preoccupied with addressing infant
outcomes: growth, obesity, health, and cognition (Colen & Ramey, 2014;
Morales et al., 2011; Neville et al., 2012). Importantly though, breastfeeding
may specifically benefit the physical and psychological health of mothers
(Labbok, 1999). Breastfeeding reduces breast and ovarian cancer risk in
many women (Friebel, Domchek, & Rebbeck, 2014; Luan et al., 2013; Möller,
Olsson, Ranstam, & Collaborative Group on Hormonal Factors in Breast
Cancer, 2002). Obesity is also an established public health concern. A recent
meta-analysis revealed that the relationship between breastfeeding and
post-pregnancy weight loss is variable (Neville, McKinley, Holmes, Spence,
& Woodside, 2014). However, in 4/5 of the most methodologically rigorous
such studies, mothers who breastfed retained less of their pregnancy weight
than did mothers who did not breast feed (Neville et al., 2014). In the moment,
breastfeeding seemingly buffers women from stress via down-regulation of
the physiological stress response system (Heinrichs, Neumann, & Ehlert,
2002). Women who breastfeed may also be more protected from developing
osteoporosis, type 2 diabetes, and hypertension later in life (Agarwal &
Stuart-Macadam, 2003; Ryan, 2012).
Mothers, however, are more than milk. Many factors contribute to
infant-feeding practices and not all mothers are able to breastfeed for a
variety of economic, medical, psychological, and cultural considerations.
Beyond the milk she provides, the mother’s body provides an “adaptively
relevant environment” for the developing infant (Hinde, 2014). Contact of
mother and infant, for example, during safe cosleeping, can contribute to a
physiological coregulation of mother and infant (McKenna, Ball, & Gettler,
2007). Skin-to-skin contact, also known as kangaroo care, influences infant
regulation in the hours after birth (Ferber & Makhoul, 2004). This behavioral
contact between the infant and mother’s bodies, the concurrent emotional
and somatosensory stimulation, likely contributes to the neurobiological

Motherhood

9

changes occurring in the maternal brain as the mother-infant bond is
established.
MOTHERHOOD CROSS-CULTURALLY
Motherhood in humans, however, is further embedded within psychological and cultural constructs (Cassidy & El Tom, 2015; Hrdy, 1999, 2009).
Recently, Faircloth considered intensive motherhood as “Identity Work.”
In light of her work on attachment parenting among mothers in the
United Kingdom, encouraged a new wave of an anthropology of parenting
and consideration of a culturally constructed moral motherhood (2009).
Indeed, culturally mediated and reinforced expectations of motherhood
actuate manifestation of attitudes, behaviors, and identify of individual
mothers. For example, among the Khmir in Tunisia, breast-feeding is
seen as “evidence of Baraka: a life-sustaining force” (Creyghton, 1992, p.
37). Baraka not only bonds a mother to her child, but the life sustaining
force permeates to all members of the household, so a healthy baby is
perceived as a blessing on the entire family. Lactation lasts 2 years and
the Khmir believe that only mother’s milk can affect the infant; if the
baby is unwell it is because of milk illness due to maternal violations
of expected behavior (Creyghton, 1992). Meehan compared trade-offs
between subsistence work and infant caregiving among Aka and Ngandu
mothers in the Central African Republic (2009). Their different subsistence patterns, the Aka are tropical forest foragers whereas the Ngandu
practice slash-and-burn horticulture influenced the works demands and
availability of helpers. Aka mothers were able to spend more time holding
their infants than did Ngandu mothers (Meehan, 2009). Mothers may
care for sons and daughters differently as reflects cultural preferences or
evolutionary adaptive allocations (Margulis, Altmann, & Ober, 1993; R.
Quinlan, M. Quinlan, & Flinn, 2005; Wander & Mattison, 2013). Moreover
motherhood can extend well into advanced years; indeed the grandmaternal
niche is a crucial human attribute and contributes to the features that
characterize human cooperative breeding (Scelza, 2009). Even within a
patrilocal society in which women live with or near their husband’s families,
they still maintain contact with their own kin (Scelza, 2011). Among the
Himba pastoralists of Namibia women maintain relationships and access
to their mothers, through periodic visitation (Scelza, 2011). Indeed the
cultural and cooperative context in which human mothers are rearing
their infants and children is experiencing a resurgence of research effort,
integrating the social transmission as well as adaptive significance of
motherhood.

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

KEY ISSUES GOING FORWARD
Here we have considered motherhood from the perspective of the mother,
rather than through the outcome of her mothering- the infant. In the
coming years and decades we will benefit from the continued investigation
of maternal behavior and the underlying neurobiology and physiology
as well as for humans within the cultural context in which motherhood
occurs. Increasingly studies are integrating multiple facets of motherhood
simultaneously which has a multiplicative rather than additive affect on our
understanding of motherhood. Of particular importance will be integrative
studies that assess the multiple pathways of maternal input to young—their
behavioral care and their physiological investment (Hinde, 2013). Such
studies will have important translational potential to world health and
public policy. The focus on motherhood and the importance to infants,
however, risks depriving mothers of personhood. Emphasizing the maternal
“exalts women as mothers and not women qua women” (Waggoner, 2013).
Disentangling the maternal from the feminine is an important and emerging
area of research in the fields of gender studies, the history of science, and
other fields in which social science and public health intersect.

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KATIE HINDE SHORT BIOGRAPHY
Katie Hinde earned her BA in Anthropology from the University of Washington in 1999, MA in Anthropology from UCLA in 2003, and PhD in Anthropology from UCLA in 2008. Her post-doctoral training was in Neuroscience
at the California National Primate Research Center, UC Davis from 2009 to
2011. In her Comparative Lactation Lab they investigate how mother’s milk
contributes to infant behavioral, psychobiological, and somatic development
in socially complex taxa, particularly humans and nonhuman primates. She
established descriptive values for rhesus macaque milk production across
lactation, and demonstrated the effects of maternal life-history and infant sex
on milk synthesis. In addition to journal publications, Hinde coedited “Building Babies: Primate Developmental Trajectories in Proximate and Ultimate
Perspective” released by Springer in 2013. Her ARMMS Program (Archive of
Rhesus Macaque Milk Samples) makes hundreds of milk samples available
to colleagues to assay for bioactive factors. Hinde is an Associate Editor and
writer for SPLASH! Milk Science Update, executive council member for the
International Society for Research in Human Milk and Lactation (2013–2015),
and showcases research on mother’s milk, breastfeeding, and lactation for the
general public, clinicians, and researchers on her blog “Mammals Suck …
Milk!”
Links: http://mammalssuck.blogspot.com;
http://www.people.fas.harvard.edu/∼khinde/contact.html.
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16

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

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Gender and the Transition to Adulthood: A Diverse Pathways View (Sociology), Ingrid Schoon
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Shinobu Kitayama and Sarah Huff



Motherhood
KATIE HINDE

Abstract
Motherhood is fundamentally the state of being a mother. In mammals this manifests as behaviorally nurturing and physiologically nourishing one’s young. The state
of motherhood requires substantial and dramatic changes in the mother’s behavior,
brain, and body. Moreover among humans, motherhood occurs within a familial,
socioeconomic, and cultural context. Among many animals, to become a mother
marks the transition to a new stage of life, from a period dedicated to growth and
development to a period of sexual maturity and productivity. Considering trade-offs
within and across the stages of the life course, known as life history theory, is essential to understand motherhood. Moreover, the interests of the mother and the infant
overlap, but are not identical, leading to conflicts of interest. Here we will consider
established and emerging topics of investigation into motherhood—from the neuron
to the society—and directions for the future.

INTRODUCTION
In 1952, John Bowlby and his colleague James Robertson presented a short
film entitled “A Two-Year-Old Goes to Hospital.” Over the course of an
eight day hospital stay, the infant deteriorated in the absence of maternal
care despite nutritional and medical support. This dramatic interruption
of the mother-infant dyad served as a window into the infant’s psychological processes in light of separation from the mother. From expanded
studies by Bowlby, cross-cultural investigations of mothers and infants
by Mary Ainsworth, and rhesus macaque experiments by Harry Harlow,
Steve Suomi, and colleagues, the mid-twentieth century laid a foundation
for Attachment Theory and established a framework for evaluating the
mother-infant dynamic, the role of the mother, and the consequences for
infants. Maternal behavioral care was demonstrated to be an important
contribution to species-typical behavioral development and physiological
regulation. This expanding research into the importance of maternal love
was a crucial repudiation of the conventional “wisdom” of regimented
infant care recommended by many prominent physicians between WWI
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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and WWII. Prior to these empirical studies, mothers were cautioned against
excessive affection—such as cuddling and soothing—directed toward the
infant (Lewis, 1982).
Notably, studies of mothers were, and remain to this day, mostly
infant-centered, that is to say, predominantly designed to investigate infant
outcomes. Progeny are the principle currency of natural selection, attracting
the interests of evolutionary biologists and behavioral ecologists. Piagetian
psychologists, Batesian linguists, and Barkerian DOHaDians1 are motivated
to understand how early environment and experiences influence cognitive
development, language acquisition, and physiological function into childhood and adulthood. Parents, clinicians, and public health advocates are
particularly motivated to optimize infant outcomes.
However, mothers, and their experience of motherhood, are more than
merely inputs into infant developmental trajectories. Depending on the
social, behavioral, or life science lens through which motherhood is assessed,
one can approach it as a state, a stage, and a construct. Fundamentally, motherhood is the state of behaviorally caring for young—after either producing
one’s own biological young as is typical, or occasionally in the case of
humans, through adoption of a nonbiological infant or child. Among many
animals, to become a mother marks the transition to a new stage of life, from
a period dedicated to growth and development to a period of sexual maturity and productivity. Considering trade-offs within and across the stages
of the life course, known as life history theory, is essential to understanding
motherhood. Across species, motherhood involves substantial changes in
behavior—not only in direct care of the infant, but also indirectly by changed
interactions with other individuals. Motherhood precipitates a cascade of
neurobiological and physiological changes that mediate infant care and
nourishment as well as transitions to the next reproductive effort. Among
humans, motherhood is also a feature of personal identity—a construct of
self, as well as a cultural construct. Here we will explore recent studies that
provide new information about motherhood and identify future directions
that enhance the translational utility of scholarly studies of motherhood.
EVOLUTIONARY CONTEXT
LIFE HISTORY THEORY
Before evaluating maternal behavioral care and physiological investment,
we must consider life history theory and parent-offspring conflict. All
biological organisms face trade-offs for allocating energy among competing
1. A reference to key scholars influencing their disciplines: cognition and Jean Piaget, linguistics and
Elizabeth Bates and Developmental Origins of Health and Disease and David P. Barker.

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processes. Drawing a parallel with Economics 101 and the “guns versus
butter model,” capital is finite and money supporting the manufacture
of one commodity is no longer available for another commodity. Such
is energy for the biological organism; a calorie can only be burned once.
Organisms have finite resources, such as energy, that are allocated to somatic
maintenance, development, and reproduction (Stearns, 1992). For examples,
among mammals, maintenance includes the physiological processes of
immune function, digestion, and endothermic thermoregulation. Development includes growth, neurogenesis, and skeletal ossification. Reproduction
requires mating, gametogenesis, and for females—pregnancy and lactation.
Mobilization of stored fat on the mother’s body for milk synthesis is fat
that is no longer available for the mother’s thermoregulation or future
reproduction. She must recover those stores before resuming estrus and the
next reproductive event (Valeggia & Ellison, 2009). As such, motherhood
occurs within a framework of necessary trade-offs. Natural selection favored
traits that produced adaptations that underlie contingencies for allocating
energy among behavioral activity and physiological processes to maximize
lifetime reproductive success (Clutton-Brock, 1991). Reproductive success
is measured as the number of offspring produced that reach reproductive
maturity across an entire reproductive career. As a result of these many
factors and constraints, mammalian mothers are expected to vary their
effort and investment in individual offspring in relation to the mother’s own
condition, the offspring’s condition, and the time point in her reproductive
career (Clutton-Brock, 1991). The many moving parts of the mother-infant
dynamic complicate greatly studies of motherhood. This is particularly true
when one considers that the mother and infant may have, to some extent,
divergent interests when they interact.
PARENT-OFFSPRING CONFLICT
Natural selection has not only acted on adaptations in mothers. The infant
plays an important role within the mother-infant dynamic. Just as mothers face trade-offs between maintenance and reproduction, so infants face
trade-offs between maintenance and growth (Stearns, 1992). Moreover the
interests of the infant and the mother are not perfectly aligned. Mothers are
equally related to each of their offspring, as offspring inherit 50% of their
genetic material, on average, from their mother. All else being equal, mothers
are predicted to allocate resources equally among their offspring. But infants
are 100% related to themselves, only 50% related to their mother and only
25–50% related to their mother’s other offspring, depending on whether their
share a father in addition to sharing a mother. Invoking Hamilton’s rule,
Trivers (1974) argued that this difference between self and relative would

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

generate parent-offspring conflict of interest over the amount and duration
of investment from the mother and adaptations in offspring to extract greater
investment from the mother. The mother-infant dynamic is therefore shaped
by an essential tension as the mother and offspring negotiate behavioral care
and physiological investment between their respective optima (Hinde, 2014).
Negotiation of these divergent interests are further complicated as within the
infant, genes of paternal origin and genes of maternal origin are also potentially in conflict (Haig, 2014). The complexity and nuance embedded within
the “symbiosis of parent–offspring interactions” are therefore a particularly
challenging area of research in the social and behavioral sciences (Rosenblum
& Moltz, 1983).
THE BEHAVIORAL BIOLOGY OF MOTHERHOOD
MATERNAL BEHAVIOR
A suite of behaviors are generally associated with motherhood and can
include protection, vigilance, nourishment, transporting, physical comforting of the young and in socially complex species, mothers may intervene on
their offspring’s behalf during social encounters. The form of these behaviors
will vary across species—for example, nourishment can take the form of
mother’s milk or provisioned foods. Physical comforting can be licking,
grooming, and huddling. Mother–infant interactions have been one of the
most prevalent and enduring research areas in anthropology, psychology,
and primatology. Primate and rodent models have been particularly useful
in understanding maternal behavior (Champagne, 2014; Champagne &
Meaney, 2001; Dettmer, Suomi, & Hinde, 2014; Phillips et al., 2014). From
these studies, we have a deep appreciation that mothers display substantial
individual variation in their behavioral care of infants. In a diversity of
animal taxa, variation in maternal care has been associated with social
rank, social environment, ecological conditions, genetic predispositions, and
prior experience rearing young (Champagne & Meaney, 2001; Fairbanks,
1993; Fairbanks & Hinde, 2013; Hrdy, 2009; Maestripieri & Mateo, 2009;
Meaney, 2001). Long-term assessment of maternal care in free-ranging rhesus
macaques on Cayo Santiago showed that females had consistent “mothering
styles,” mother infant interactions of proximity, contact, and rejection
were consistent across age periods and between infants (Berman, 1990).
Cross-fostering experiments have been conducted with rhesus macaques at
Yerkes that demonstrate that maternal–infant interactions are genetically
coadapted (Maestripieri, 2004). More rejecting mothers produce infants that
are more inclined to make contact and vice versa (Maestripieri, 2004). In a

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series of landmark studies, Rosenblum and colleagues manipulated foraging demands on mothers to understand how it changed their behavioral
interactions with their infants and other monkeys in the social group. The
researchers created three foraging conditions; (i) high foraging demand
(HFD) 90–100 monkey biscuits were hidden in 1000 food holes (110% of
their normal diet), (ii) low foraging demand (LFD) 600 biscuits were hidden
in 1000 food holes, and (iii) variable foraging demand (VFD) in which food
was provided either the HFD or LFD condition on a 2-week cycle. The
VFD condition seemed to be psychologically demanding for mothers. These
mothers were less attentive to their infants, broke contact with their infant
significantly more frequently, and infants expended greater effort to reestablish contact than in the HFD or LFD groups. Among the adults in the VFD
condition, including mothers, there were more hierarchical interactions (e.g.,
aggression, displacement) and less grooming. These studies provide strong
evidence that unpredictable environmental conditions are particularly
difficult on mothers even though the foraging demands were intermediate
between the HFD and LFD. The variable aspect of the VFD condition was
more stressful and had a greater affect on maternal care than even the
condition in which foraging demands were always high (Rosenblum &
Andrews, 1994; Rosenblum & Paully, 1984). This pioneering work continues
to this day, revealing that individuals reared under VFD conditions have
deficits in adulthood and transmit variable foraging demand consequences
across generations (Coplan et al., 2001; Coplan et al., 2006; Kinnally et al.,
2013). Increasingly, studies of maternal behavior have expanded beyond
ethology to understand the neurobiology and physiology of motherhood
(Clancy, Hinde, & Rutherford, 2013), or rather the maternal brain and the
maternal body.
THE MATERNAL BRAIN
The mother-infant bond is established shortly after birth via neurobiological
mechanisms. The dopaminergic and oxytocinergic neuroendocrine pathways underlie the mother-infant bond—neurobiologically motivating and
rewarding mothers for maternal care. Naturally occurring variation in the
production, reception, and distribution of dopamine and oxytocin within the
maternal brain, among other neurotransmitters, can contribute to variation
in maternal responsivity, attachment, and behavioral care (Carter, Lederhendler, & Kirkpatrick, 1999; Feldman, Gordon, Schneiderman, Weisman,
& Zagoory-Sharon, 2010; Insel & Young, 2001; Saltzman & Maestripieri,
2011; Strathearn, Fonagy, Amico, & Montague, 2009). Most research into
the maternal brain has occurred in the rodent model because of ethical,
experimental, and logistical considerations. Much less is understood in

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the primate brain, including humans, although new imaging technologies
are affording researchers more options for investigating brain changes as a
function of motherhood. In human mothers, the brain undergoes morphological changes in the weeks and months after giving birth. Specifically, the
amount of grey matter, rich with neuronal cell bodies, increases in regions
of the brain that are critical for sensory perception, emotion processing, and
motivation (Kim et al., 2010). These morphological changes are consistent
with functional imaging showing increased oxygen utilization and glucose
uptake in these same regions during the early months of motherhood
(reviewed in Kim et al., 2010). Most intriguingly, mothers who self-reported
the most positive thoughts about their baby at the outset of the study
showed the greatest increases in grey matter months later (Kim et al., 2010).
This result suggests that perceptions of motherhood and mother-infant
dynamics may positively feedback, enhancing maternal behavior, but this
remains speculative in the absence of more data. Higher circulating oxytocin
in human mothers has been associated with increased maternal bonding
behaviors, such as gazing at, checking on, and speaking to the infant, as well
as affectionately touching and positive affect regarding the infant (Feldman,
Weller, Zagoory-Sharon, & Levine, 2007; Gordon, Zagoory-Sharon, Leckman, & Feldman, 2010). Although not directly measuring the maternal brain,
they still provide insight into the physiology of motherhood. Moreover,
many of the hormones that mediate behavioral care in the brain also exert
important peripheral effects that are critical for mothers during lactation.
Particularly important, prolactin stimulates milk production while oxytocin
triggers milk letdown for transfer to the infant (Lincoln, 1983) and among
mammals, milk is a particular marker of motherhood.
THE MATERNAL BODY
The synthesis of milk by mammary glands is the defining characteristic of
our mammalian class. Unfortunately, we still know relatively little about
postnatal maternal physiological investment. For example, much more
research effort has been dedicated to understanding pregnancy than aspects
of lactation, particularly breast milk composition (Figure 1). Mother’s milk
consists of hundreds, possibly thousands of bioactive constituents, including
numerous fats, proteins, sugars, vitamins, minerals, immunofactors, and
hormones as well as water that hydrates the neonate (Hinde & Milligan, 2011;
Neville et al., 2012). How mothers pay the costs of lactation vary according to
life history theory. Mothers energetically support lactation via a diversity of
tactics and strategies that vary across individuals and species. Lactation can
be supported by mobilizing body reserves (Oftedal, 2000); basically mothers
dissolve parts of themselves to feed their young. Others rely to a greater

Motherhood

Number of articles x 1000

800

7

769.4

700
600
500
400
WHAT?!

300
200
72.7

100

32.6

0
Pregnancy

Lactation

Breast milk

2.3
Breast milk
composition

Figure 1 The number of articles returned as a result of keyword searches in
PubMed, a database maintained by the United States National Library of Medicine
(NLM) at the National Institutes of Health. Key word search conducted on June 1,
2014.

extent on dietary intake to sustain lactation. Conceptually these approaches
can be characterized as “capital” and “income” breeding (Jönsson, 1997).
However in practice most species exhibit multiple tactics to sustain lactation,
relying on the mobilization of maternal reserves and dietary intake, as well
as behavioral compensation and metabolic efficiencies (Gittleman & Thompson, 1988; Speakman, 2008). The tactics utilized to sustain lactation can therefore influence interbirth interval and consequently lifetime reproductive
success. In baboons, chimpanzees, and humans, weight loss from mobilizing
bodily reserves to sustain lactation, suppresses ovulation and subsequent
conception is contingent on maternal recovery (Emery Thompson, 2013).
Given that mothers face trade-offs and rely on different tactics during
lactation, substantial variation in milk synthesis is to be expected. Indeed a
growing body of literature evaluating mother’s milk from an evolutionary
perspective, demonstrates that mother’s milk varies across time, across
individuals, across populations, and across species (Hinde & Milligan,
2011; Neville et al. 2012; Oftedal & Iverson 1995; Skibiel, Downing, Orr, &
Hood, 2013). First-time mothers generally produce lower volumes of milk
during lactation than do experienced, multiparous females in humans,
monkeys, pinnipeds, rodents, and bovids (reviewed in Hinde, Carpenter,
Clay, & Bradford, 2014; Hinde, Power, & Oftedal, 2009). Maternal diet can
also predict milk composition (Hinde & Milligan, 2011; Milligan & Bazinet,
2008; Skibiel et al., 2013). Maternal parasite load is associated with lower
milk production in cows (Perri et al., 2011) and milk fat concentration in
rhesus monkeys (Hinde, 2007). Moreover, although mothers synthesize
milk, accumulating evidence suggests that sometimes milk differs between

8

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

sons and daughters in red deer, bank voles, cows, wallabies, rhesus monkeys, and humans (reviewed in Hinde et al., 2014). Some milk bioactives,
such as glucocorticoids, vary substantially among mothers (Grey, Davis,
Sandman, & Glynn, 2013) and has recently been shown to reflect maternal
life history (Hinde et al., 2014). Better knowledge of sources of variation,
especially for milk constituents linked to maternal condition can lead to
more personalized clinical recommendations for mothers and their infants.
Such knowledge has the potential to inform decisions about breast-feeding
initiation and duration, improve replacement and supplemental formula
compositions, and husbandry practices and nursery rearing of mammalian
young in research or agricultural settings.
Typically the public discourse on breastfeeding among WEIRD societies
[Western, educated, industrialized, rich, and democratic (Henrich, Heine,
& Norenzayan, 2010)] has remained preoccupied with addressing infant
outcomes: growth, obesity, health, and cognition (Colen & Ramey, 2014;
Morales et al., 2011; Neville et al., 2012). Importantly though, breastfeeding
may specifically benefit the physical and psychological health of mothers
(Labbok, 1999). Breastfeeding reduces breast and ovarian cancer risk in
many women (Friebel, Domchek, & Rebbeck, 2014; Luan et al., 2013; Möller,
Olsson, Ranstam, & Collaborative Group on Hormonal Factors in Breast
Cancer, 2002). Obesity is also an established public health concern. A recent
meta-analysis revealed that the relationship between breastfeeding and
post-pregnancy weight loss is variable (Neville, McKinley, Holmes, Spence,
& Woodside, 2014). However, in 4/5 of the most methodologically rigorous
such studies, mothers who breastfed retained less of their pregnancy weight
than did mothers who did not breast feed (Neville et al., 2014). In the moment,
breastfeeding seemingly buffers women from stress via down-regulation of
the physiological stress response system (Heinrichs, Neumann, & Ehlert,
2002). Women who breastfeed may also be more protected from developing
osteoporosis, type 2 diabetes, and hypertension later in life (Agarwal &
Stuart-Macadam, 2003; Ryan, 2012).
Mothers, however, are more than milk. Many factors contribute to
infant-feeding practices and not all mothers are able to breastfeed for a
variety of economic, medical, psychological, and cultural considerations.
Beyond the milk she provides, the mother’s body provides an “adaptively
relevant environment” for the developing infant (Hinde, 2014). Contact of
mother and infant, for example, during safe cosleeping, can contribute to a
physiological coregulation of mother and infant (McKenna, Ball, & Gettler,
2007). Skin-to-skin contact, also known as kangaroo care, influences infant
regulation in the hours after birth (Ferber & Makhoul, 2004). This behavioral
contact between the infant and mother’s bodies, the concurrent emotional
and somatosensory stimulation, likely contributes to the neurobiological

Motherhood

9

changes occurring in the maternal brain as the mother-infant bond is
established.
MOTHERHOOD CROSS-CULTURALLY
Motherhood in humans, however, is further embedded within psychological and cultural constructs (Cassidy & El Tom, 2015; Hrdy, 1999, 2009).
Recently, Faircloth considered intensive motherhood as “Identity Work.”
In light of her work on attachment parenting among mothers in the
United Kingdom, encouraged a new wave of an anthropology of parenting
and consideration of a culturally constructed moral motherhood (2009).
Indeed, culturally mediated and reinforced expectations of motherhood
actuate manifestation of attitudes, behaviors, and identify of individual
mothers. For example, among the Khmir in Tunisia, breast-feeding is
seen as “evidence of Baraka: a life-sustaining force” (Creyghton, 1992, p.
37). Baraka not only bonds a mother to her child, but the life sustaining
force permeates to all members of the household, so a healthy baby is
perceived as a blessing on the entire family. Lactation lasts 2 years and
the Khmir believe that only mother’s milk can affect the infant; if the
baby is unwell it is because of milk illness due to maternal violations
of expected behavior (Creyghton, 1992). Meehan compared trade-offs
between subsistence work and infant caregiving among Aka and Ngandu
mothers in the Central African Republic (2009). Their different subsistence patterns, the Aka are tropical forest foragers whereas the Ngandu
practice slash-and-burn horticulture influenced the works demands and
availability of helpers. Aka mothers were able to spend more time holding
their infants than did Ngandu mothers (Meehan, 2009). Mothers may
care for sons and daughters differently as reflects cultural preferences or
evolutionary adaptive allocations (Margulis, Altmann, & Ober, 1993; R.
Quinlan, M. Quinlan, & Flinn, 2005; Wander & Mattison, 2013). Moreover
motherhood can extend well into advanced years; indeed the grandmaternal
niche is a crucial human attribute and contributes to the features that
characterize human cooperative breeding (Scelza, 2009). Even within a
patrilocal society in which women live with or near their husband’s families,
they still maintain contact with their own kin (Scelza, 2011). Among the
Himba pastoralists of Namibia women maintain relationships and access
to their mothers, through periodic visitation (Scelza, 2011). Indeed the
cultural and cooperative context in which human mothers are rearing
their infants and children is experiencing a resurgence of research effort,
integrating the social transmission as well as adaptive significance of
motherhood.

10

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

KEY ISSUES GOING FORWARD
Here we have considered motherhood from the perspective of the mother,
rather than through the outcome of her mothering- the infant. In the
coming years and decades we will benefit from the continued investigation
of maternal behavior and the underlying neurobiology and physiology
as well as for humans within the cultural context in which motherhood
occurs. Increasingly studies are integrating multiple facets of motherhood
simultaneously which has a multiplicative rather than additive affect on our
understanding of motherhood. Of particular importance will be integrative
studies that assess the multiple pathways of maternal input to young—their
behavioral care and their physiological investment (Hinde, 2013). Such
studies will have important translational potential to world health and
public policy. The focus on motherhood and the importance to infants,
however, risks depriving mothers of personhood. Emphasizing the maternal
“exalts women as mothers and not women qua women” (Waggoner, 2013).
Disentangling the maternal from the feminine is an important and emerging
area of research in the fields of gender studies, the history of science, and
other fields in which social science and public health intersect.

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280(1768), 20131359.

KATIE HINDE SHORT BIOGRAPHY
Katie Hinde earned her BA in Anthropology from the University of Washington in 1999, MA in Anthropology from UCLA in 2003, and PhD in Anthropology from UCLA in 2008. Her post-doctoral training was in Neuroscience
at the California National Primate Research Center, UC Davis from 2009 to
2011. In her Comparative Lactation Lab they investigate how mother’s milk
contributes to infant behavioral, psychobiological, and somatic development
in socially complex taxa, particularly humans and nonhuman primates. She
established descriptive values for rhesus macaque milk production across
lactation, and demonstrated the effects of maternal life-history and infant sex
on milk synthesis. In addition to journal publications, Hinde coedited “Building Babies: Primate Developmental Trajectories in Proximate and Ultimate
Perspective” released by Springer in 2013. Her ARMMS Program (Archive of
Rhesus Macaque Milk Samples) makes hundreds of milk samples available
to colleagues to assay for bioactive factors. Hinde is an Associate Editor and
writer for SPLASH! Milk Science Update, executive council member for the
International Society for Research in Human Milk and Lactation (2013–2015),
and showcases research on mother’s milk, breastfeeding, and lactation for the
general public, clinicians, and researchers on her blog “Mammals Suck …
Milk!”
Links: http://mammalssuck.blogspot.com;
http://www.people.fas.harvard.edu/∼khinde/contact.html.
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Social Class and Parental Investment in Children (Sociology), Anne H.
Gauthier
Changing Family Patterns (Sociology), Kathleen Gerson and Stacy Torres
Family Relationships and Development (Psychology), Joan E. Grusec

16

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

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Becoming Adult: Meanings of Markers to Adulthood (Sociology), Richard A.
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Michaela Kreyenfeld
Gender and the Transition to Adulthood: A Diverse Pathways View (Sociology), Ingrid Schoon
Born This Way: Thinking Sociologically about Essentialism (Sociology),
Kristen Schilt
Divorce (Sociology), Juho Härkönen
Modeling Life Course Structure: The Triple Helix (Sociology), Tom Schuller
Social Change and Entry to Adulthood (Sociology), Jeylan T. Mortimer
Culture and Cognition (Sociology), Karen A. Cerulo
Intersectionality and the Development of Self and Identity (Psychology),
Margarita Azmitia and Virginia Thomas
Temporal Identity Integration as a Core Developmental Process (Psychology),
Moin Syed and Lauren L. Mitchell
Cooperative Breeding and Human Evolution (Anthropology), Karen L.
Kramer
Kin-Directed Behavior in Primates (Anthropology), Carol M. Berman
Cultural Neuroscience: Connecting Culture, Brain, and Genes (Psychology),
Shinobu Kitayama and Sarah Huff


Motherhood
KATIE HINDE

Abstract
Motherhood is fundamentally the state of being a mother. In mammals this manifests as behaviorally nurturing and physiologically nourishing one’s young. The state
of motherhood requires substantial and dramatic changes in the mother’s behavior,
brain, and body. Moreover among humans, motherhood occurs within a familial,
socioeconomic, and cultural context. Among many animals, to become a mother
marks the transition to a new stage of life, from a period dedicated to growth and
development to a period of sexual maturity and productivity. Considering trade-offs
within and across the stages of the life course, known as life history theory, is essential to understand motherhood. Moreover, the interests of the mother and the infant
overlap, but are not identical, leading to conflicts of interest. Here we will consider
established and emerging topics of investigation into motherhood—from the neuron
to the society—and directions for the future.

INTRODUCTION
In 1952, John Bowlby and his colleague James Robertson presented a short
film entitled “A Two-Year-Old Goes to Hospital.” Over the course of an
eight day hospital stay, the infant deteriorated in the absence of maternal
care despite nutritional and medical support. This dramatic interruption
of the mother-infant dyad served as a window into the infant’s psychological processes in light of separation from the mother. From expanded
studies by Bowlby, cross-cultural investigations of mothers and infants
by Mary Ainsworth, and rhesus macaque experiments by Harry Harlow,
Steve Suomi, and colleagues, the mid-twentieth century laid a foundation
for Attachment Theory and established a framework for evaluating the
mother-infant dynamic, the role of the mother, and the consequences for
infants. Maternal behavioral care was demonstrated to be an important
contribution to species-typical behavioral development and physiological
regulation. This expanding research into the importance of maternal love
was a crucial repudiation of the conventional “wisdom” of regimented
infant care recommended by many prominent physicians between WWI
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

and WWII. Prior to these empirical studies, mothers were cautioned against
excessive affection—such as cuddling and soothing—directed toward the
infant (Lewis, 1982).
Notably, studies of mothers were, and remain to this day, mostly
infant-centered, that is to say, predominantly designed to investigate infant
outcomes. Progeny are the principle currency of natural selection, attracting
the interests of evolutionary biologists and behavioral ecologists. Piagetian
psychologists, Batesian linguists, and Barkerian DOHaDians1 are motivated
to understand how early environment and experiences influence cognitive
development, language acquisition, and physiological function into childhood and adulthood. Parents, clinicians, and public health advocates are
particularly motivated to optimize infant outcomes.
However, mothers, and their experience of motherhood, are more than
merely inputs into infant developmental trajectories. Depending on the
social, behavioral, or life science lens through which motherhood is assessed,
one can approach it as a state, a stage, and a construct. Fundamentally, motherhood is the state of behaviorally caring for young—after either producing
one’s own biological young as is typical, or occasionally in the case of
humans, through adoption of a nonbiological infant or child. Among many
animals, to become a mother marks the transition to a new stage of life, from
a period dedicated to growth and development to a period of sexual maturity and productivity. Considering trade-offs within and across the stages
of the life course, known as life history theory, is essential to understanding
motherhood. Across species, motherhood involves substantial changes in
behavior—not only in direct care of the infant, but also indirectly by changed
interactions with other individuals. Motherhood precipitates a cascade of
neurobiological and physiological changes that mediate infant care and
nourishment as well as transitions to the next reproductive effort. Among
humans, motherhood is also a feature of personal identity—a construct of
self, as well as a cultural construct. Here we will explore recent studies that
provide new information about motherhood and identify future directions
that enhance the translational utility of scholarly studies of motherhood.
EVOLUTIONARY CONTEXT
LIFE HISTORY THEORY
Before evaluating maternal behavioral care and physiological investment,
we must consider life history theory and parent-offspring conflict. All
biological organisms face trade-offs for allocating energy among competing
1. A reference to key scholars influencing their disciplines: cognition and Jean Piaget, linguistics and
Elizabeth Bates and Developmental Origins of Health and Disease and David P. Barker.

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3

processes. Drawing a parallel with Economics 101 and the “guns versus
butter model,” capital is finite and money supporting the manufacture
of one commodity is no longer available for another commodity. Such
is energy for the biological organism; a calorie can only be burned once.
Organisms have finite resources, such as energy, that are allocated to somatic
maintenance, development, and reproduction (Stearns, 1992). For examples,
among mammals, maintenance includes the physiological processes of
immune function, digestion, and endothermic thermoregulation. Development includes growth, neurogenesis, and skeletal ossification. Reproduction
requires mating, gametogenesis, and for females—pregnancy and lactation.
Mobilization of stored fat on the mother’s body for milk synthesis is fat
that is no longer available for the mother’s thermoregulation or future
reproduction. She must recover those stores before resuming estrus and the
next reproductive event (Valeggia & Ellison, 2009). As such, motherhood
occurs within a framework of necessary trade-offs. Natural selection favored
traits that produced adaptations that underlie contingencies for allocating
energy among behavioral activity and physiological processes to maximize
lifetime reproductive success (Clutton-Brock, 1991). Reproductive success
is measured as the number of offspring produced that reach reproductive
maturity across an entire reproductive career. As a result of these many
factors and constraints, mammalian mothers are expected to vary their
effort and investment in individual offspring in relation to the mother’s own
condition, the offspring’s condition, and the time point in her reproductive
career (Clutton-Brock, 1991). The many moving parts of the mother-infant
dynamic complicate greatly studies of motherhood. This is particularly true
when one considers that the mother and infant may have, to some extent,
divergent interests when they interact.
PARENT-OFFSPRING CONFLICT
Natural selection has not only acted on adaptations in mothers. The infant
plays an important role within the mother-infant dynamic. Just as mothers face trade-offs between maintenance and reproduction, so infants face
trade-offs between maintenance and growth (Stearns, 1992). Moreover the
interests of the infant and the mother are not perfectly aligned. Mothers are
equally related to each of their offspring, as offspring inherit 50% of their
genetic material, on average, from their mother. All else being equal, mothers
are predicted to allocate resources equally among their offspring. But infants
are 100% related to themselves, only 50% related to their mother and only
25–50% related to their mother’s other offspring, depending on whether their
share a father in addition to sharing a mother. Invoking Hamilton’s rule,
Trivers (1974) argued that this difference between self and relative would

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

generate parent-offspring conflict of interest over the amount and duration
of investment from the mother and adaptations in offspring to extract greater
investment from the mother. The mother-infant dynamic is therefore shaped
by an essential tension as the mother and offspring negotiate behavioral care
and physiological investment between their respective optima (Hinde, 2014).
Negotiation of these divergent interests are further complicated as within the
infant, genes of paternal origin and genes of maternal origin are also potentially in conflict (Haig, 2014). The complexity and nuance embedded within
the “symbiosis of parent–offspring interactions” are therefore a particularly
challenging area of research in the social and behavioral sciences (Rosenblum
& Moltz, 1983).
THE BEHAVIORAL BIOLOGY OF MOTHERHOOD
MATERNAL BEHAVIOR
A suite of behaviors are generally associated with motherhood and can
include protection, vigilance, nourishment, transporting, physical comforting of the young and in socially complex species, mothers may intervene on
their offspring’s behalf during social encounters. The form of these behaviors
will vary across species—for example, nourishment can take the form of
mother’s milk or provisioned foods. Physical comforting can be licking,
grooming, and huddling. Mother–infant interactions have been one of the
most prevalent and enduring research areas in anthropology, psychology,
and primatology. Primate and rodent models have been particularly useful
in understanding maternal behavior (Champagne, 2014; Champagne &
Meaney, 2001; Dettmer, Suomi, & Hinde, 2014; Phillips et al., 2014). From
these studies, we have a deep appreciation that mothers display substantial
individual variation in their behavioral care of infants. In a diversity of
animal taxa, variation in maternal care has been associated with social
rank, social environment, ecological conditions, genetic predispositions, and
prior experience rearing young (Champagne & Meaney, 2001; Fairbanks,
1993; Fairbanks & Hinde, 2013; Hrdy, 2009; Maestripieri & Mateo, 2009;
Meaney, 2001). Long-term assessment of maternal care in free-ranging rhesus
macaques on Cayo Santiago showed that females had consistent “mothering
styles,” mother infant interactions of proximity, contact, and rejection
were consistent across age periods and between infants (Berman, 1990).
Cross-fostering experiments have been conducted with rhesus macaques at
Yerkes that demonstrate that maternal–infant interactions are genetically
coadapted (Maestripieri, 2004). More rejecting mothers produce infants that
are more inclined to make contact and vice versa (Maestripieri, 2004). In a

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series of landmark studies, Rosenblum and colleagues manipulated foraging demands on mothers to understand how it changed their behavioral
interactions with their infants and other monkeys in the social group. The
researchers created three foraging conditions; (i) high foraging demand
(HFD) 90–100 monkey biscuits were hidden in 1000 food holes (110% of
their normal diet), (ii) low foraging demand (LFD) 600 biscuits were hidden
in 1000 food holes, and (iii) variable foraging demand (VFD) in which food
was provided either the HFD or LFD condition on a 2-week cycle. The
VFD condition seemed to be psychologically demanding for mothers. These
mothers were less attentive to their infants, broke contact with their infant
significantly more frequently, and infants expended greater effort to reestablish contact than in the HFD or LFD groups. Among the adults in the VFD
condition, including mothers, there were more hierarchical interactions (e.g.,
aggression, displacement) and less grooming. These studies provide strong
evidence that unpredictable environmental conditions are particularly
difficult on mothers even though the foraging demands were intermediate
between the HFD and LFD. The variable aspect of the VFD condition was
more stressful and had a greater affect on maternal care than even the
condition in which foraging demands were always high (Rosenblum &
Andrews, 1994; Rosenblum & Paully, 1984). This pioneering work continues
to this day, revealing that individuals reared under VFD conditions have
deficits in adulthood and transmit variable foraging demand consequences
across generations (Coplan et al., 2001; Coplan et al., 2006; Kinnally et al.,
2013). Increasingly, studies of maternal behavior have expanded beyond
ethology to understand the neurobiology and physiology of motherhood
(Clancy, Hinde, & Rutherford, 2013), or rather the maternal brain and the
maternal body.
THE MATERNAL BRAIN
The mother-infant bond is established shortly after birth via neurobiological
mechanisms. The dopaminergic and oxytocinergic neuroendocrine pathways underlie the mother-infant bond—neurobiologically motivating and
rewarding mothers for maternal care. Naturally occurring variation in the
production, reception, and distribution of dopamine and oxytocin within the
maternal brain, among other neurotransmitters, can contribute to variation
in maternal responsivity, attachment, and behavioral care (Carter, Lederhendler, & Kirkpatrick, 1999; Feldman, Gordon, Schneiderman, Weisman,
& Zagoory-Sharon, 2010; Insel & Young, 2001; Saltzman & Maestripieri,
2011; Strathearn, Fonagy, Amico, & Montague, 2009). Most research into
the maternal brain has occurred in the rodent model because of ethical,
experimental, and logistical considerations. Much less is understood in

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

the primate brain, including humans, although new imaging technologies
are affording researchers more options for investigating brain changes as a
function of motherhood. In human mothers, the brain undergoes morphological changes in the weeks and months after giving birth. Specifically, the
amount of grey matter, rich with neuronal cell bodies, increases in regions
of the brain that are critical for sensory perception, emotion processing, and
motivation (Kim et al., 2010). These morphological changes are consistent
with functional imaging showing increased oxygen utilization and glucose
uptake in these same regions during the early months of motherhood
(reviewed in Kim et al., 2010). Most intriguingly, mothers who self-reported
the most positive thoughts about their baby at the outset of the study
showed the greatest increases in grey matter months later (Kim et al., 2010).
This result suggests that perceptions of motherhood and mother-infant
dynamics may positively feedback, enhancing maternal behavior, but this
remains speculative in the absence of more data. Higher circulating oxytocin
in human mothers has been associated with increased maternal bonding
behaviors, such as gazing at, checking on, and speaking to the infant, as well
as affectionately touching and positive affect regarding the infant (Feldman,
Weller, Zagoory-Sharon, & Levine, 2007; Gordon, Zagoory-Sharon, Leckman, & Feldman, 2010). Although not directly measuring the maternal brain,
they still provide insight into the physiology of motherhood. Moreover,
many of the hormones that mediate behavioral care in the brain also exert
important peripheral effects that are critical for mothers during lactation.
Particularly important, prolactin stimulates milk production while oxytocin
triggers milk letdown for transfer to the infant (Lincoln, 1983) and among
mammals, milk is a particular marker of motherhood.
THE MATERNAL BODY
The synthesis of milk by mammary glands is the defining characteristic of
our mammalian class. Unfortunately, we still know relatively little about
postnatal maternal physiological investment. For example, much more
research effort has been dedicated to understanding pregnancy than aspects
of lactation, particularly breast milk composition (Figure 1). Mother’s milk
consists of hundreds, possibly thousands of bioactive constituents, including
numerous fats, proteins, sugars, vitamins, minerals, immunofactors, and
hormones as well as water that hydrates the neonate (Hinde & Milligan, 2011;
Neville et al., 2012). How mothers pay the costs of lactation vary according to
life history theory. Mothers energetically support lactation via a diversity of
tactics and strategies that vary across individuals and species. Lactation can
be supported by mobilizing body reserves (Oftedal, 2000); basically mothers
dissolve parts of themselves to feed their young. Others rely to a greater

Motherhood

Number of articles x 1000

800

7

769.4

700
600
500
400
WHAT?!

300
200
72.7

100

32.6

0
Pregnancy

Lactation

Breast milk

2.3
Breast milk
composition

Figure 1 The number of articles returned as a result of keyword searches in
PubMed, a database maintained by the United States National Library of Medicine
(NLM) at the National Institutes of Health. Key word search conducted on June 1,
2014.

extent on dietary intake to sustain lactation. Conceptually these approaches
can be characterized as “capital” and “income” breeding (Jönsson, 1997).
However in practice most species exhibit multiple tactics to sustain lactation,
relying on the mobilization of maternal reserves and dietary intake, as well
as behavioral compensation and metabolic efficiencies (Gittleman & Thompson, 1988; Speakman, 2008). The tactics utilized to sustain lactation can therefore influence interbirth interval and consequently lifetime reproductive
success. In baboons, chimpanzees, and humans, weight loss from mobilizing
bodily reserves to sustain lactation, suppresses ovulation and subsequent
conception is contingent on maternal recovery (Emery Thompson, 2013).
Given that mothers face trade-offs and rely on different tactics during
lactation, substantial variation in milk synthesis is to be expected. Indeed a
growing body of literature evaluating mother’s milk from an evolutionary
perspective, demonstrates that mother’s milk varies across time, across
individuals, across populations, and across species (Hinde & Milligan,
2011; Neville et al. 2012; Oftedal & Iverson 1995; Skibiel, Downing, Orr, &
Hood, 2013). First-time mothers generally produce lower volumes of milk
during lactation than do experienced, multiparous females in humans,
monkeys, pinnipeds, rodents, and bovids (reviewed in Hinde, Carpenter,
Clay, & Bradford, 2014; Hinde, Power, & Oftedal, 2009). Maternal diet can
also predict milk composition (Hinde & Milligan, 2011; Milligan & Bazinet,
2008; Skibiel et al., 2013). Maternal parasite load is associated with lower
milk production in cows (Perri et al., 2011) and milk fat concentration in
rhesus monkeys (Hinde, 2007). Moreover, although mothers synthesize
milk, accumulating evidence suggests that sometimes milk differs between

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

sons and daughters in red deer, bank voles, cows, wallabies, rhesus monkeys, and humans (reviewed in Hinde et al., 2014). Some milk bioactives,
such as glucocorticoids, vary substantially among mothers (Grey, Davis,
Sandman, & Glynn, 2013) and has recently been shown to reflect maternal
life history (Hinde et al., 2014). Better knowledge of sources of variation,
especially for milk constituents linked to maternal condition can lead to
more personalized clinical recommendations for mothers and their infants.
Such knowledge has the potential to inform decisions about breast-feeding
initiation and duration, improve replacement and supplemental formula
compositions, and husbandry practices and nursery rearing of mammalian
young in research or agricultural settings.
Typically the public discourse on breastfeeding among WEIRD societies
[Western, educated, industrialized, rich, and democratic (Henrich, Heine,
& Norenzayan, 2010)] has remained preoccupied with addressing infant
outcomes: growth, obesity, health, and cognition (Colen & Ramey, 2014;
Morales et al., 2011; Neville et al., 2012). Importantly though, breastfeeding
may specifically benefit the physical and psychological health of mothers
(Labbok, 1999). Breastfeeding reduces breast and ovarian cancer risk in
many women (Friebel, Domchek, & Rebbeck, 2014; Luan et al., 2013; Möller,
Olsson, Ranstam, & Collaborative Group on Hormonal Factors in Breast
Cancer, 2002). Obesity is also an established public health concern. A recent
meta-analysis revealed that the relationship between breastfeeding and
post-pregnancy weight loss is variable (Neville, McKinley, Holmes, Spence,
& Woodside, 2014). However, in 4/5 of the most methodologically rigorous
such studies, mothers who breastfed retained less of their pregnancy weight
than did mothers who did not breast feed (Neville et al., 2014). In the moment,
breastfeeding seemingly buffers women from stress via down-regulation of
the physiological stress response system (Heinrichs, Neumann, & Ehlert,
2002). Women who breastfeed may also be more protected from developing
osteoporosis, type 2 diabetes, and hypertension later in life (Agarwal &
Stuart-Macadam, 2003; Ryan, 2012).
Mothers, however, are more than milk. Many factors contribute to
infant-feeding practices and not all mothers are able to breastfeed for a
variety of economic, medical, psychological, and cultural considerations.
Beyond the milk she provides, the mother’s body provides an “adaptively
relevant environment” for the developing infant (Hinde, 2014). Contact of
mother and infant, for example, during safe cosleeping, can contribute to a
physiological coregulation of mother and infant (McKenna, Ball, & Gettler,
2007). Skin-to-skin contact, also known as kangaroo care, influences infant
regulation in the hours after birth (Ferber & Makhoul, 2004). This behavioral
contact between the infant and mother’s bodies, the concurrent emotional
and somatosensory stimulation, likely contributes to the neurobiological

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9

changes occurring in the maternal brain as the mother-infant bond is
established.
MOTHERHOOD CROSS-CULTURALLY
Motherhood in humans, however, is further embedded within psychological and cultural constructs (Cassidy & El Tom, 2015; Hrdy, 1999, 2009).
Recently, Faircloth considered intensive motherhood as “Identity Work.”
In light of her work on attachment parenting among mothers in the
United Kingdom, encouraged a new wave of an anthropology of parenting
and consideration of a culturally constructed moral motherhood (2009).
Indeed, culturally mediated and reinforced expectations of motherhood
actuate manifestation of attitudes, behaviors, and identify of individual
mothers. For example, among the Khmir in Tunisia, breast-feeding is
seen as “evidence of Baraka: a life-sustaining force” (Creyghton, 1992, p.
37). Baraka not only bonds a mother to her child, but the life sustaining
force permeates to all members of the household, so a healthy baby is
perceived as a blessing on the entire family. Lactation lasts 2 years and
the Khmir believe that only mother’s milk can affect the infant; if the
baby is unwell it is because of milk illness due to maternal violations
of expected behavior (Creyghton, 1992). Meehan compared trade-offs
between subsistence work and infant caregiving among Aka and Ngandu
mothers in the Central African Republic (2009). Their different subsistence patterns, the Aka are tropical forest foragers whereas the Ngandu
practice slash-and-burn horticulture influenced the works demands and
availability of helpers. Aka mothers were able to spend more time holding
their infants than did Ngandu mothers (Meehan, 2009). Mothers may
care for sons and daughters differently as reflects cultural preferences or
evolutionary adaptive allocations (Margulis, Altmann, & Ober, 1993; R.
Quinlan, M. Quinlan, & Flinn, 2005; Wander & Mattison, 2013). Moreover
motherhood can extend well into advanced years; indeed the grandmaternal
niche is a crucial human attribute and contributes to the features that
characterize human cooperative breeding (Scelza, 2009). Even within a
patrilocal society in which women live with or near their husband’s families,
they still maintain contact with their own kin (Scelza, 2011). Among the
Himba pastoralists of Namibia women maintain relationships and access
to their mothers, through periodic visitation (Scelza, 2011). Indeed the
cultural and cooperative context in which human mothers are rearing
their infants and children is experiencing a resurgence of research effort,
integrating the social transmission as well as adaptive significance of
motherhood.

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

KEY ISSUES GOING FORWARD
Here we have considered motherhood from the perspective of the mother,
rather than through the outcome of her mothering- the infant. In the
coming years and decades we will benefit from the continued investigation
of maternal behavior and the underlying neurobiology and physiology
as well as for humans within the cultural context in which motherhood
occurs. Increasingly studies are integrating multiple facets of motherhood
simultaneously which has a multiplicative rather than additive affect on our
understanding of motherhood. Of particular importance will be integrative
studies that assess the multiple pathways of maternal input to young—their
behavioral care and their physiological investment (Hinde, 2013). Such
studies will have important translational potential to world health and
public policy. The focus on motherhood and the importance to infants,
however, risks depriving mothers of personhood. Emphasizing the maternal
“exalts women as mothers and not women qua women” (Waggoner, 2013).
Disentangling the maternal from the feminine is an important and emerging
area of research in the fields of gender studies, the history of science, and
other fields in which social science and public health intersect.

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KATIE HINDE SHORT BIOGRAPHY
Katie Hinde earned her BA in Anthropology from the University of Washington in 1999, MA in Anthropology from UCLA in 2003, and PhD in Anthropology from UCLA in 2008. Her post-doctoral training was in Neuroscience
at the California National Primate Research Center, UC Davis from 2009 to
2011. In her Comparative Lactation Lab they investigate how mother’s milk
contributes to infant behavioral, psychobiological, and somatic development
in socially complex taxa, particularly humans and nonhuman primates. She
established descriptive values for rhesus macaque milk production across
lactation, and demonstrated the effects of maternal life-history and infant sex
on milk synthesis. In addition to journal publications, Hinde coedited “Building Babies: Primate Developmental Trajectories in Proximate and Ultimate
Perspective” released by Springer in 2013. Her ARMMS Program (Archive of
Rhesus Macaque Milk Samples) makes hundreds of milk samples available
to colleagues to assay for bioactive factors. Hinde is an Associate Editor and
writer for SPLASH! Milk Science Update, executive council member for the
International Society for Research in Human Milk and Lactation (2013–2015),
and showcases research on mother’s milk, breastfeeding, and lactation for the
general public, clinicians, and researchers on her blog “Mammals Suck …
Milk!”
Links: http://mammalssuck.blogspot.com;
http://www.people.fas.harvard.edu/∼khinde/contact.html.
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