Early Stage Romantic Love is Associated with Reduced Daily Cortisol Production

The Molecular Basis of Love

Love as a complex interplay of emotions and behaviors is underpinned by an intricate network of neurobiological mechanisms. This review provides insight into the molecular basis of love, focusing on the role of key hormones and neuromodulators. The aim of the paper is to report how these biochemical messengers influence various aspects of love, including attraction, attachment, and long-term bonding. By examining the effects of hormones such as dopamine, oxytocin, vasopressin, and serotonin, we aim to elucidate the intricate relationship between biology and behavior. Additionally, the potential impact of modern lifestyle factors on hormonal balance and their subsequent influence on love and social interactions are outlined. This review provides a useful overview of the molecular underpinnings of love, offering insights into the biological mechanisms that shape human relationships.

Silence between words: Is solitude important for relatedness?

Chronic loneliness is a risk factor for physical and health problems, in part due to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system. In contrast, temporary moments of positive solitude (passing good times alone and not feeling lonely) appear to have positive effects on mental health, social life, and creativity, and seems to be a buffer against loneliness. Herein, three ways of how solitude may have positive effects on health and relatedness are discussed, namely effects on enhancement of mind-wandering, interoceptive awareness, and spirituality. Solitude may facilitate (1) activation of the default mode network (DMN) underlying mind-wandering including daydreaming about other people; (2) activation of brain areas supporting interoceptive awareness; (3) deactivation of prefrontal cortex, or deactivation and decreased connectivity of the DMN, giving raise to susceptibility to spiritual experiences. The capacity to handle and enjoy solitude is a developmental process that may be difficult for many persons. Craving for social connections and external stimulation with digital technologies (e.g., internet, smartphones, social media) might be interfering with the development of the capacity for solitude and thereby increasing loneliness; this might be partly due to impaired interoceptive awareness and impaired functional mind-wandering (common in solitude). Congruently, overuse of digital technologies was associated with reduced activity, and reduced gray matter volume and density, in brain areas supporting interoceptive awareness, as well as with decreased connectivity of the DMN supporting creative insights. Solitude has been a relatively dismissed topic in neuroscience and health sciences, but a growing number of studies is highlighting its importance for well-being.

Romantic love evolved by co-opting mother-infant bonding

For 25 years, the predominant evolutionary theory of romantic love has been Fisher's theory of independent emotion systems. That theory suggests that sex drive, romantic attraction (romantic love), and attachment are associated with distinct neurobiological and endocrinological systems which evolved independently of each other. Psychological and neurobiological evidence, however, suggest that a competing theory requires attention. A theory of co-opting mother-infant bonding sometime in the recent evolutionary history of humans may partially account for the evolution of romantic love. I present a case for this theory and a new approach to the science of romantic love drawing on human psychological, neurobiological, and (neuro)endocrinological studies as well as animal studies. The hope is that this theoretical review, along with other publications, will generate debate in the literature about the merits of the theory of co-opting mother-infant bonding and a new evolutionary approach to the science of romantic love.

Toward consistent reporting of sample characteristics in studies investigating the biological mechanisms of romantic love

In this non-systematic review, we consider the sample reporting practices of 42 studies up to and including 2021 investigating the biological mechanisms of romantic love (i.e., 31 neuroimaging studies, nine endocrinological studies, one genetics study, and one combined neuroimaging and genetics study). We searched scientific databases using key terms and drew on our and other authors' knowledge to identify studies that investigated the mechanisms associated with romantic love using neuroimaging, endocrinological, and genetic methods. Only studies with a group or entire sample experiencing romantic love were included. The aim was to collate all relevant studies and determine the comparability of studies and ability to assess the generalizability of findings. We summarize how these studies report sex/gender, age, romantic love, relationship duration/time in love, and sample descriptors. We then outline the case for promoting comparability and the ability to determine generalizability in future studies. The findings indicate a limited ability to compare studies' samples or make an assessment of the generalizability of findings. Existing studies are not representative of the general population in a particular country or globally. We conclude by presenting ideas about how best to report sex, age, romantic love characteristics, relationship status, time in love, relationship duration, relationship satisfaction, type of unrequited love, sexual activity, cultural characteristics, socio-economic status, student status, and method-relevant descriptors. If our ideas are adopted, in part or in whole, we expect the comparability of studies to increase. Adopting our ideas will also make it easier to make an assessment of the generalizability of findings.

Romantic Love and Sleep Variations: Potential Proximate Mechanisms and Evolutionary Functions

This article provides a narrative review of what is known about romantic love and sleep variations and provides possible explanations for the association. Romantic love and sleep are described using a comprehensive, unifying framework advocated by Tinbergen. We summarise the findings of studies investigating the relationship between romantic love and sleep. Sleep variations are associated with romantic love in adolescents and young adults. We then detail some proximate mechanisms that may contribute to sleep variations in people experiencing romantic love before considering potential evolutionary functions of sleep variations in people experiencing romantic love. The relationship between symptoms of psychopathology and sleep variations in people experiencing romantic love is described. With the current state of knowledge, it is not possible to determine whether sleep variations associated with romantic love are adaptations or by-products of romantic love. We conclude by proposing areas for future research.

CortiLove: A pilot study on hair steroids in the context of being in love and separation

While romantic infatuation and separation influence psychological and physiological functioning, the hypothalamic-pituitary-adrenal axis with its biomarkers cortisol, dehydroepiandrosterone (DHEA), and progesterone central for coping and distress has been scarcely researched in this context. In particular, endocrine hair analyses assumed to be more valid than saliva or blood assessments for studying long-term processes have not yet been conducted in the context of romantic love. Thus, 101 female subjects in phases of infatuation (n = 16), separation (n = 14), long-term relationships (n = 40), and singlehood (n = 31) reported psychological distress and provided 1 cm hair samples for the assessment of long-term integrated cortisol, DHEA, and progesterone over the last month. Separated, infatuated, and single women exhibited higher cortisol levels than those in a long-term relationship (all ps ≤ .031), while self-reported distress was only evident in separated individuals. Further, no group differences for progesterone (p = .602), but higher DHEA levels in the separation (p = .009) and single group (p = .016) compared to the long-term relationship group were detected. This is the first study showing that compared to women in long-term relationships, infatuation, separation, and single groups exhibit higher levels of physiological, but not necessarily self-reported indicators of distress. These findings, albeit on a very small and preliminary sample, are discussed in the context of the stress-buffering effect of relationships, and provide important starting points for bigger, more balanced studies combining multimodal self-report and biological markers in psychological research of romantic love.

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Higher hair cortisol in separation, infatuation, singlehood vs. stable relationship.

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Higher hair DHEA only in separation and singlehood vs. stable relationship.

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No group difference for progesterone.

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Divergence of physiological and self-reported indicators of distress.

Proximate and Ultimate Perspectives on Romantic Love

Romantic love is a phenomenon of immense interest to the general public as well as to scholars in several disciplines. It is known to be present in almost all human societies and has been studied from a number of perspectives. In this integrative review, we bring together what is known about romantic love using Tinbergen’s “four questions” framework originating from evolutionary biology. Under the first question, related to mechanisms, we show that it is caused by social, psychological mate choice, genetic, neural, and endocrine mechanisms. The mechanisms regulating psychopathology, cognitive biases, and animal models provide further insights into the mechanisms that regulate romantic love. Under the second question, related to development, we show that romantic love exists across the human lifespan in both sexes. We summarize what is known about its development and the internal and external factors that influence it. We consider cross-cultural perspectives and raise the issue of evolutionary mismatch. Under the third question, related to function, we discuss the fitness-relevant benefits and costs of romantic love with reference to mate choice, courtship, sex, and pair-bonding. We outline three possible selective pressures and contend that romantic love is a suite of adaptions and by-products. Under the fourth question, related to phylogeny, we summarize theories of romantic love’s evolutionary history and show that romantic love probably evolved in concert with pair-bonds in our recent ancestors. We describe the mammalian antecedents to romantic love and the contribution of genes and culture to the expression of modern romantic love. We advance four potential scenarios for the evolution of romantic love. We conclude by summarizing what Tinbergen’s four questions tell us, highlighting outstanding questions as avenues of potential future research, and suggesting a novel ethologically informed working definition to accommodate the multi-faceted understanding of romantic love advanced in this review.

Universality of the Triangular Theory of Love: Adaptation and Psychometric Properties of the Triangular Love Scale in 25 Countries

The Triangular Theory of Love (measured with Sternberg's Triangular Love Scale - STLS) is a prominent theoretical concept in empirical research on love. To expand the culturally homogeneous body of previous psychometric research regarding the STLS, we conducted a large-scale cross-cultural study with the use of this scale. In total, we examined more than 11,000 respondents, but as a result of applied exclusion criteria, the final analyses were based on a sample of 7332 participants from 25 countries (from all inhabited continents). We tested configural invariance, metric invariance, and scalar invariance, all of which confirmed the cultural universality of the theoretical construct of love analyzed in our study. We also observed that levels of love components differ depending on relationship duration, following the dynamics suggested in the Triangular Theory of Love. Supplementary files with all our data, including results on love intensity across different countries along with STLS versions adapted in a few dozen languages, will further enable more extensive research on the Triangular Theory of Love.

Romantic Love and Reproductive Hormones in Women

Increased reproductive success is among the most commonly proposed adaptive functions of romantic love. Here, we tested if hormonal changes associated with falling in love may co-vary with hormonal profiles that predict increased fecundity in women. We compared blood serum levels of estradiol (E2, E2/T), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), free testosterone (fT), and cortisol (CT), measured in the early follicular phase of the menstrual cycle in single women (N = 69) and in women at the beginning of a romantic heterosexual relationship who reported being in love with their partner (N = 47). Participants were healthy, regularly cycling women aged 24 to 33 who did not use hormonal contraception. We found that women in love had higher levels of gonadotropins (FSH, LH) and lower testosterone levels compared to single women who were not in love. These groups of women did not, however, differ in terms of estradiol, prolactin, or cortisol levels.

I love you from the bottom of my hypothalamus: The role of stress physiology in romantic pair bond formation and maintenance

Monogamous pair bonds helped solve ancestral problems pertinent to our survival as a species. In order for these pair bonds to succeed, biological systems were co-opted to support and reinforce attachment bonds through feelings of pleasure and reward. One of the major biological systems that may play an important role in the formation of romantic attachments is the stress response system (autonomic nervous system and hypothalamic-pituitary-adrenal axis). Research suggests attraction, mate preference, and emotional connectedness may be supported by the activation or inhibition of the stress response system. Further, as romantic relationships progress, new findings suggest partners' physiological patterns coalesce, potentially serving a regulatory function that reinforces the pair bond and affects overall well-being. Based on this evidence, the current paper puts forth the Physiology of Romantic Pair Bond Initiation and Maintenance Model, which will provide researchers with a new perspective on the function of the stress response system in romantic relationships.