A species out of its evolutionary context

Anthropologists describe contemporary Western societies with the acronym WEIRD: Western, Educated, Industrialised, Rich and Democratic. WEIRD societies represent a striking departure from conditions in which Homo sapiens evolved, and child-rearing systems illustrate this particularly sharply. We lived as hunter-gatherers for more than 95% of our evolutionary history and therefore, although present-day hunter-gatherers are not living replicas of ancestral societies, they can still offer valuable insight into the caregiving practices to which we may be adapted. The anthropological evidence strongly suggests that alloparenting – childcare support from individuals other than the parents – has been one of the most important human evolutionary adaptations. ^{Reference Hrdy1} Among the BaYaka, for example, we found that children typically have around eight alloparents per day, who provide close to half of their care, including responding to their crying. ^{Reference Chaudhary, Salali and Swanepoel2} Anthropologists have studied alloparenting patterns in numerous other hunter-gatherer societies and, although patterns are not uniform, levels of alloparental support are consistently high when considered in contrast to WEIRD populations. ^{Reference Hrdy1} Therefore, it is plausible that human maternal psychology evolved to function with substantially more support than most WEIRD mothers receive, potentially resulting in an evolutionary mismatch where an organism is exposed to social or environmental conditions that differ from those to which some trait of the organism is adapted, thereby increasing the risk of maladaptation or disease.

This high level of support is facilitated by the fact that hunter-gatherers live in close-knit camps of around 20–80 friends and relatives spanning several generations. ^{Reference Chaudhary, Salali and Swanepoel2} A further consequence of this residence pattern is that mothers have immediate access to informational support from highly experienced, trusted older women who can offer guidance on parenting issues such as breastfeeding and infant sleeping. This continuous, trusted access to advice contrasts starkly with the parenting ecology of WEIRD societies, where mothers instead encounter an abundance of often inconsistent, conflicting and sometimes inaccurate information, delivered online and via health professionals with whom they have no close personal relationship, making it difficult to know which guidance to trust.

Another related impact of this intergenerational communal residence pattern is the extensive caregiving experience gained prior to parenthood. Children and adolescents are consistently found to provide substantial allocare across hunter-gatherer societies, and often begin to do so more than a decade before becoming parents themselves. ^{Reference Chaudhary, Salali and Swanepoel2} This is entirely at odds with our experience as clinicians in the UK, where many new mothers report minimal caregiving experience prior to giving birth.

The clinical consequences of mismatch

We postulate that the mismatches outlined above are among the factors contributing to the high rates of perinatal depression and anxiety seen in WEIRD societies. We do not claim that these rates are the highest globally (indeed, prevalence is frequently higher in low- and middle-income settings), but rather that reduced alloparental support is one pathway that may contribute to this burden. Insufficient social support is among the risk factors most consistently identified for postnatal depression. Independent effects have been found for support from partners, family and friends: the availability of the last two is substantially higher in hunter-gatherer societies. ^{Reference Sufredini, Catling, Zugai and Chang3} We do not claim that weak support networks are the sole cause, but the convergent evidence supports the mismatch hypothesis as a plausible and clinically useful explanatory framework. What the evolutionary framing adds, beyond a conventional social determinants account, is an explanation for why isolation is so reliably pathogenic: in addition to support being instrumentally useful, human maternal psychology was shaped in an environment in which social support was far more extensive and crucial to offspring survival.

As with postnatal depression, poor social support is a key risk factor for both pre- and postnatal anxiety ^{Reference Sufredini, Catling, Zugai and Chang3} . From a mismatch perspective, this may be partially attributed to mothers in WEIRD societies having lower pre-parenthood experience in caregiving, and reduced access to trusted parenting guidance, compared with what has been normative over our species’ history. Qualitative research has found that many mothers are distressed due to feeling (a) poorly prepared for motherhood; (b) a need for more advice and reassurance after leaving hospital postpartum; and (c) unaware of which information to trust. ^{Reference Slomian, Emonts, Vigneron, Acconcia, Glowacz and Reginster4} Hunter-gatherer women are less likely to be faced with these kinds of difficulties because they live in multigenerational camps with trusted friends and relatives, and already have many years of experience caring for young children prior to motherhood. By extension, the breastfeeding difficulties faced by many women in WEIRD cultures, often accompanied by intense guilt and shame, ^{Reference Jackson, De Pascalis, Harrold and Fallon5} may be partially attributable to a reduction in intergenerational knowledge transmission. Unlike most other mammals, humans and other primates rely on social learning as well as instinct for successful breastfeeding. ^{Reference Volk6} Such learning opportunities are argued to be less available in contemporary WEIRD societies than in non-WEIRD societies, and especially in comparison with ancestral societies where co-residence patterns facilitated knowledge-sharing. ^{Reference Volk6}

The problem of intensive mothering narratives

A central feature of WEIRD parenting culture is the ideology of intensive mothering: the expectation that a good mother should be self-sufficient, instinctively competent and almost wholly responsible for her child’s well-being. ^{Reference Hays7} This individualised model of responsibility stands in sharp contrast to the shared, alloparental caregiving that characterised our evolutionary past. It also helps to explain why breastfeeding and other early difficulties are so readily experienced as personal failure: they are felt as a failure to meet the standards of ‘good’ or intensive mothering. Such narratives are reinforced through parenting culture, sometimes health professional attitudes and popular misreadings of attachment theory, which is often taken to prescribe intensive, exclusive maternal care. Attachment theory in fact describes a child’s need for consistent, responsive care that alloparents can and did share, rather than a requirement that it be provided by the mother alone. When mothers internalise the intensive mothering ideal, the predictable consequences of an under-supported, mismatched environment become experienced as personal failure. Perinatal mental health clinicians are well placed to recognise and challenge these narratives directly.

Implications for clinical practice

We suggest implications at the levels of the consultation, service and policy, each informed by the evolutionary perspective and the framework it offers to consider not only the symptoms with which a patient presents, but also the environmental conditions that may contribute to them.

At the level of the consultation, the evolutionary framework offers a psychoeducational resource. When a mother understands not simply that social support reduces postnatal depression but why (that human maternal psychology evolved amid extensive caregiving support, so that becoming overwhelmed in isolation reflects a predictable mismatch rather than personal failure), the clinical encounter can shift. As one example of ongoing work in this spirit, the authors are involved in a psychoeducational project conveying this message in a leaflet co-produced with women under the care of a perinatal psychiatry unit (see Declaration of interest); it remains preliminary and unevaluated, and is offered as hypothesis-generating rather than as evidence of efficacy, with a systematic study planned. More broadly, this evolutionary perspective resonates with the ethos of specialist perinatal mental healthcare and its emphasis on holistic, ‘whole-system’ formulation, which situates a mother within her relational and social context rather than within her symptoms alone.

The evolutionary framework also offers a lens through which the effectiveness of established treatments can be understood. A systematic review and meta-analysis of randomised controlled trials found cognitive–behavioural therapy strongly recommended for perinatal depression across the severity spectrum, with interpersonal therapy (IPT) and peer support also recommended. ^{Reference Radoš, Ganho-Ávila, Rodriguez-Muñoz, Bina, Kittel-Schneider and Lambregtse-van den Berg8} Viewed through an evolutionary lens, the active components of these interventions map onto the very social deficits the mismatch hypothesis identifies as pathogenic: IPT addresses interpersonal conflict and isolation; group and peer support rebuild communal caregiving opportunities and networks of trusted information exchange; and the therapeutic alliance itself can partly restore the trusted, experienced guidance once provided within the community. The same review noted that community-based delivery by non-specialist providers can be effective, which, from an evolutionary standpoint, is consistent with the value of trusted social support. This should not, however, be taken to diminish the essential role of specialist perinatal mental health services, which remain indispensable across the full spectrum and severity of perinatal mental illness, a caution of particular importance amid pressures on public spending. Prioritising the continuity and frequency of care may help build the rapport and trust that mothers, understandably, emphasise a desire for. ^{Reference Slomian, Emonts, Vigneron, Acconcia, Glowacz and Reginster4}

At the public health level, current nursery regulations, parental leave policies and housing design reflect implicit assumptions about the sufficiency of the nuclear family as a child-rearing unit of which the evolutionary perspective invites scrutiny. Achievable near-term steps include commissioning peer support programmes that build caregiving networks around new mothers, routinely mapping social support networks in perinatal care plans and early identification of women at risk of social isolation. Longer-term possibilities include further investment into intergenerational care facilities and communal housing projects, which are increasing in popularity but remain rare and unfunded. These represent partial reinstatements of the alloparenting ecology in which our species evolved, but first require formal evaluation, and careful design, because co-living is not universally beneficial and can introduce its own stressors.

Caveats and future directions

Several caveats deserve note. First, we do not wish to idealise hunter-gatherer life; our references to these societies serve to identify domains in which mismatches plausibly occur. Importantly, this is not equivalent to suggesting that mental health difficulties do not exist among hunter-gatherers. A study of the Hadza of Tanzania indicates that postpartum mood disturbances may not be uncommon in their society. ^{Reference Herlosky, Benyshek, Mabulla, Pollom and Crittenden9} However, in contrast to WEIRD societies, social support did not emerge as a relevant risk factor, which is what our argument would predict where alloparental support is near universal. Instead, postpartum mood disturbances among Hadza mothers appear to be driven by other factors, such as concerns tied to high rates of infant mortality.

Evolutionary anthropology identifies what human maternal psychology is probably adapted to, not what it must be exposed to. The alloparenting narrative must be applied with cultural sensitivity and psychoeducation co-produced with diverse communities, including those outside WEIRD societies who may already practise forms of cooperative childrearing.