Mothers' prenatal distress accelerates adrenal pubertal development in daughters

Human life history schedules vary, partly, because of adaptive, plastic responses to early-life conditions. Little is known about how prenatal conditions relate to puberty timing. We hypothesized that fetal exposure to adversity may induce an adaptive response in offspring maturational tempo. In a longitudinal study of 253 mother-child dyads followed for 15 years, we investigated if fetal exposure to maternal psychological distress related to children's adrenarche and gonadarche schedules, assessed by maternal and child report and by dehydroepiandrosterone sulfate (DHEA-S), testosterone, and estradiol levels. We found fetal exposure to elevated maternal prenatal psychological distress predicted earlier adrenarche and higher DHEA-S levels in girls, especially first-born girls, and that associations remained after covarying indices of postnatal adversity. No associations were observed for boys or for gonadarche in girls. Adrenarche orchestrates the social-behavioral transition from juvenility to adulthood; therefore, significant findings for adrenarche, but not gonadarche, suggest that prenatal maternal distress instigates an adaptive strategy in which daughters have earlier social-behavioral maturation. The stronger effect in first-borns suggests that, in adverse conditions, it is in the mother's adaptive interest for her daughter to hasten social maturation, but not necessarily sexual maturation, because it would prolong the duration of the daughter allomothering younger siblings. We postulate a novel evolutionary framework that human mothers may calibrate the timing of first-born daughters' maturation in a way that optimizes their own reproductive success.

Human neuronal maturation comes of age: cellular mechanisms and species differences

The delayed and prolonged postmitotic maturation of human neurons, compared with neurons from other species, may contribute to human-specific cognitive abilities and neurological disorders. Here we review the mechanisms of neuronal maturation, applying lessons from model systems to understand the specific features of protracted human cortical maturation and species differences. We cover cell-intrinsic features of neuronal maturation, including transcriptional, epigenetic and metabolic mechanisms, as well as cell-extrinsic features, including the roles of activity and synapses, the actions of glial cells and the contribution of the extracellular matrix. We discuss evidence for species differences in biochemical reaction rates, the proposed existence of an epigenetic maturation clock and the contributions of both general and modular mechanisms to species-specific maturation timing. Finally, we suggest approaches to measure, improve and accelerate the maturation of human neurons in culture, examine crosstalk and interactions among these different aspects of maturation and propose conceptual models to guide future studies.

Adaptation across the Lifespan: Towards a Processual Evolutionary Explanation of Human Development

This paper argues that the project of a lifespan perspective in developmental psychology has not yet been systematically pursued. Overall, the number of age-specific papers far outweighs the number of lifespan approaches, and even approaches that focus on the lifespan as a whole are often restricted to adulthood. Further, there is a lack of approaches that examine cross-lifespan relationships. However, the lifespan perspective has brought with it a "processual turn" that suggests an examination of developmental regulatory processes that are either operative across the lifespan or develop across the lifespan. Accommodative adjustment of goals and evaluations in response to obstacles, loss, and threat is discussed as an example of such a process. Not only is it prototypical of efficacy and change of developmental regulation across the lifespan, but at the same time it makes clear that stability (e.g., of the self)-as a possible outcome of accommodation-is not an alternative to, but a variant of development. Explaining how accommodative adaptation changes, in turn, requires a broader perspective. For this purpose, an evolutionary approach to developmental psychology is proposed that not only views human development as a product of phylogenesis, but also applies the central concepts of the theory of evolution (adaptation and history) directly to ontogeny. The challenges, conditions, and limitations of such a theoretical application of adaptation to human development are discussed.

The evolution of the adolescent growth spurt: Urinary biomarkers of bone turnover in wild chimpanzees (Pan troglodytes)

Life history theory addresses how organisms balance development and reproduction. Mammals usually invest considerable energy into growth in infancy, and they do so incrementally less until reaching adult body size, when they shift energy to reproduction. Humans are unusual in having a long adolescence when energy is invested in both reproduction and growth, including rapid skeletal growth around puberty. Although many primates, especially in captivity, experience accelerated growth in mass around puberty, it remains unclear whether this represents skeletal growth. Without data on skeletal growth in nonhuman primates, anthropologists have often assumed the adolescent growth spurt is uniquely human, and hypotheses for its evolution have focused on other uniquely human traits. The lack of data is largely due to methodological difficulties of assessing skeletal growth in wild primates. Here, we use two urinary markers of bone turnover-osteocalcin and collagen-to study skeletal growth in a large, cross-sectional sample of wild chimpanzees (Pan troglodytes) at Ngogo, Kibale National Park, Uganda. For both bone turnover markers, we found a nonlinear effect of age, which was largely driven by males. For male chimpanzees, values for osteocalcin and collagen peaked at age 9.4 years and 10.8 years, respectively, which corresponds to early and middle adolescence. Notably, collagen values increased from 4.5 to 9 years, suggesting faster growth during early adolescence compared to late infancy. Biomarker levels plateaued at 20 years in both sexes, suggesting skeletal growth continues until then. Additional data, notably on females and infants of both sexes, are needed, as are longitudinal samples. However, our cross-sectional analysis suggests an adolescent growth spurt in the skeleton of chimpanzees, especially for males. Biologists should avoid claiming that the adolescent growth spurt is uniquely human, and hypotheses for the patterns of human growth should consider variation in our primate relatives.

Evolutionary game model of migraine based on the human brain hypersensitivity

Based on all studies published up to 2020, the prevalence of migraine worldwide is approximately 14%, although it varies regionally. Despite being one of the most disabling diseases, migraine still exists through natural selection and is prevalent today. This raises the question of what evolutionary advantages have led to the survival of migraine. The ultimate answer to this question should be found in evolution; however, there is no clear explanation yet. Notably, all the genes that cause migraine make the sensory organs and cortex of the migraine sufferer hypersensitive. In a state of hypersensitivity, the brain could recognize external threats easily. Game theory is a useful tool for explaining evolution in terms of genes. Just as the Hawk–Dove game, which has two strategies (aggressive and passive) and four fitness values, an evolutionary game between a migraineur and a non-migraineur, which shows two phenotypes (more sensitive and less sensitive) and four fitness values, can be played if a migraineur quickly recognizes a predator and informs a non-migraineur of its appearance and the non-migraineur later helps the migraineur escape from danger. This study aimed to explore the evolutionary mechanics of migraine that can be modeled. Furthermore, it tried to define why the human brain's hypersensitivity is a prerequisite for developing this evolutionary game model.

The energetics of childhood: Current knowledge and insights into human variation, evolution, and health

How organisms capture and ultimately use metabolic energy-a limiting resource of life-has profound implications for understanding evolutionary legacies and current patterns of phenotypic variation, adaptation, and health. Energetics research among humans has a rich history in biological anthropology and beyond. The energetics of childhood, however, remains relatively underexplored. This shortcoming is notable given the accepted importance of childhood in the evolution of the unique human life history pattern as well as the known sensitivity of childhood development to local environments and lived experiences. In this review, I have three objectives: (1) To overview current knowledge regarding how children acquire and use energy, highlighting work among diverse human populations and pointing to recent advances and remaining areas of uncertainty; (2) To discuss key applications of this knowledge for understanding human variation, evolution, and health; (3) To recommend future avenues for research. A growing body of evidence supports a model of trade-offs and constraint in childhood energy expenditure. This model, combined with advancements on topics such as the energetics of immune activity, the brain, and the gut, provides insights into the evolution of extended human subadulthood and the nature of variation in childhood development, lifetime phenotype, and health.

Proximate and Ultimate Mechanisms of Human Father-child Rough-and-tumble Play

The aim of this contribution is to attempt to understand the adaptive functions of father-child rough-and-tumble play (RTP) in humans. We first present a synthesis of the known proximate and ultimate mechanisms of peer-peer RTP in mammals and compare human parent-child RTP with peer-peer RTP. Next, we examine the possible biological adaptive functions of father-child RTP in humans, by comparing paternal behavior in humans versus biparental animal species, in light of the activation relationship theory and the neurobiological basis of fathering. Analysis of analogies reveals that the endocrine profile of fathers is highly variable across species, compared to that of mothers. This can be interpreted as fathers' evolutionary adjustment to specific environmental conditions affecting the care of the young. Given the high unpredictability and risk-taking features of RTP, we conclude that human adult-child RTP appears to have a biological adaptive function, one of 'opening to the world'.

Systems biology of human aging: A Fibonacci time series model

Fractals are everywhere in nature, particularly at the interfaces where matter or energy must be transferred, since they maximize surface area while minimizing energy losses. Temporal fractals have been well studied at micro scales in human biology, but have received comparatively little attention at broader macro scales. In this paper, we describe a fractal time series model of human aging from a systems biology perspective. This model examines how intrinsic aging rates are shaped by entropy and Fibonacci fractal dynamics, with implications for the emergence of key life cycle traits. This proposition is supported by research findings. The finding of an intrinsic aging rate rooted in Fibonacci fractal dynamics represents a new predictive paradigm in evolutionary biology.

The influence of climate and population structure on East Asian skeletal morphology

Recent studies have shown that global variation in body proportions is more complex than previously thought as some traits formerly associated with climate adaptation are better explained by geographic proximity and neutral evolutionary forces. While the recent incorporation of quantitative genetic methodologies has improved understanding of patterns related to climate in Africa, Europe, and the Americas, Asia remains underrepresented in recent and historic studies of body form. As ecogeographic studies tend to focus on male morphology, potential sex differences in features influenced by climate remain largely unexplored. Skeletal measurements encompassing the dimensions of the skull, pelvis, limbs, hands, and feet were collected from male (n = 459) and female (n = 442) remains curated in 13 collections across seven countries in East Asia (n = 901). Osteological data were analyzed with sex and minimum temperature as covariates adjusted by autosomal single-nucleotide polymorphism population genetic distance using univariate Bayesian linear mixed models, and credible intervals were calculated for each trait. Analysis supports a relationship between specific traits and climate as well as providing the magnitude of response in both sexes. After accounting for genetic distance between populations, greater association between climate and morphology was found in postcranial traits, with the relationship between climate and the skull limited primarily to breadth measurements. Larger body size is associated with colder climates with most measurements increasing with decreased temperature. The same traits were not always associated with climate for males and females nor correlated with the same intensity for both sexes. The varied directional association with climate for different regions of the skeleton and between the sexes underscores the necessity of future ecogeographic research to holistically evaluate body form and to look for sex-specific patterns to better understand population responses to environmental stresses.

Rates of ecological knowledge learning in Pemba, Tanzania: Implications for childhood evolution

Humans live in diverse, complex niches where survival and reproduction are conditional on the acquisition of knowledge. Humans also have long childhoods, spending more than a decade before they become net producers. Whether the time needed to learn has been a selective force in the evolution of long human childhood is unclear, because there is little comparative data on the growth of ecological knowledge throughout childhood. We measured ecological knowledge at different ages in Pemba, Zanzibar (Tanzania), interviewing 93 children and teenagers between 4 and 26 years. We developed Bayesian latent-trait models to estimate individual knowledge and its association with age, activities, household family structure and education. In the studied population, children learn during the whole pre-reproductive period, but at varying rates, with the fastest increases in young children. Sex differences appear during middle childhood and are mediated by participation in different activities. In addition to providing a detailed empirical investigation of the relationship between knowledge acquisition and childhood, this study develops and documents computational improvements to the modelling of knowledge development.

Mediating role of the default mode network on parental acceptance/warmth and psychopathology in youth

Humans are reliant on their caregivers for an extended period of time, offering numerous opportunities for environmental factors, such as parental attitudes and behaviors, to impact brain development. The default mode network is a neural system encompassing the medial prefrontal cortex, posterior cingulate cortex, precuneus, and temporo-parietal junction, which is implicated in aspects of cognition and psychopathology. Delayed default mode network maturation in children and adolescents has been associated with greater general dimensional psychopathology, and positive parenting behaviors have been suggested to serve as protective mechanisms against atypical default mode network development. The current study aimed to extend the existing research by examining whether within- default mode network resting-state functional connectivity would mediate the relation between parental acceptance/warmth and youth psychopathology. Data from the Adolescent Brain and Cognitive Development study, which included a community sample of 9,366 children ages 8.9-10.9 years, were analyzed to test this prediction. Results demonstrated a significant mediation, where greater parental acceptance/warmth predicted greater within- default mode network resting-state functional connectivity, which in turn predicted lower externalizing, but not internalizing symptoms, at baseline and 1-year later. Our study provides preliminary support for the notion that positive parenting behaviors may reduce the risk for psychopathology in youth through their influence on the default mode network.

Let’s Play at Digging

Extractive foraging tasks, such as digging, are broadly practiced among hunter-gatherer populations in different ecological conditions. Despite tuber-gathering tasks being widely practiced by children and adolescents, little research has focused on the physical traits associated with digging ability. Here, we assess how age and energetic expenditure affect the performance of this extractive task. Using an experimental approach, the energetic cost of digging to extract simulated tubers is evaluated in a sample of 40 urban children and adolescents of both sexes to measure the intensity of the physical effort and the influence of several anatomical variables. Digging is a moderately vigorous activity for inexperienced girls and boys from 8 to 14 years old, and it requires significant physical effort depending on strength and body size. However, extracting subterranean resources is a task that may be performed effectively without previous training. Sex-specific and age-specific differences in the net energy expenditure of digging were detected, even though both sexes exhibited similar proficiency levels when performing the task. Our results highlight that both boys and girls spend considerable energy while digging, with differences largely driven by body size and age. Other factors beyond ability and experience, such as strength and body size, may influence the proficiency of juveniles in performing certain physically intensive foraging tasks, such as gathering tubers.

Theoretical Reproductive Outcomes of the Sexual Conflict in Humans

This paper presents an updated mathematical model of the evolutionary dynamics of the sexual conflict ("battle of the sexes") and its simulated reproductive outcomes. The authors highlight a whole range of life-history traits unique to our species, such as prolonged childhood, growth in parental care, etc. Based on these biosocial premises, the sexual conflict between men and women shifts into the mathematical realm of the "Prisoner's Dilemma" game. The evolutionarily stable strategy of mutual rejection of parenthood would be dominant with this PD strategy in both parents; oscillation dynamics predicted in previous models would not be expected. Despite fatal theoretical prediction of the PD evolutionary game, the newish genetic data of the EPP rates in the historical populations reveals prevalence of cooperation between both sexes, predominantly utilizing the monogamous form of sexuality. Presumably, this sexual norm could have potentially ensured reproductive success in the societies in the past.

The Evolution of Human Infancy: Why It Helps to Be Helpless

Humans have a prolonged childhood, which begins with an immature developmental state at birth. We take care of these helpless infants through a variety of cultural adaptations, including material culture, provisioning of food, and shared child care. Our species has long been characterized as having secondary altriciality, but an examination of human life history shows that we are fundamentally precocial, despite seeming helpless at birth. Human babies are also relatively large and overall require substantial attention and energy from caregivers. Previous work has focused on how culture permits us to give birth to helpless young and how our cultural adaptation solves problems stemming from encephalization. The birth of these dependent, costly creatures poses challenges but also creates opportunities by enhancing the development of social and emotional relationships with caregivers as well as language acquisition and enculturation.

Childhood in social learning models with changing environments: Implications for human evolution

Childhood is a time of learning, both individually and through social interactions. But the vulnerability inherent in childhood represents a fitness cost: individuals do not have progeny during childhood, and childhood is a net drain of familial or group resources. In this study we model childhood in resource acquisition scenarios where social learning through observation competes with learning through innovation across multiple generations in a variety of environments. In general, observing others allows useful knowledge to be gained more efficiently than self-exploration and may result in significantly greater resource acquisition. However, social learning needing a lengthy childhood to develop advanced cognitive ability may offset the net fitness advantage that might otherwise be gained. Through simulations we demonstrate that individuals with a substantial childhood burden acquire more lifetime resources by observing others than do individuals with negligible childhood costs using self-exploration, as long as the environment is fairly stable. This advantage decreases as the environment becomes less predictable, and reverses in rapidly changing environments where knowledge is unreliable. These results suggest that hominid evolution, with vastly growing cognitive abilities and a longer, more vulnerable childhood, may have been facilitated in similarly stable environments. On the other hand, hominid populations may have been particularly vulnerable to environmental instability. We apply this insight to the Out of Africa Homo sapiens migration roughly 50,000 years ago and show consistency with the serial founder model that best fits current archeological and genetic evidence. Our findings are important for models of social learning, especially those that describe the emergence and spread of Homo sapiens.

Gathering Is Not Only for Girls : No Influence of Energy Expenditure on the Onset of Sexual Division of Labor

In some small-scale societies, a sexual division of labor is common. For subadult hunter-gatherers, the onset of this division dates to middle childhood and the start of puberty; however, there is apparently no physiological explanation for this timing. The present study uses an experimental approach to evaluate possible energetic differences by sex in gathering-related activities. The energetic cost of gathering-related activities was measured in a sample of 42 subjects of both sexes aged between 8 and 14 years. Body mass and other anthropometric variables were also recorded. Our results show that the energetic differences in the simulated gathering activities depend only on body mass. Both sexes expend a similar amount of energy during locomotion activities related to gathering. Discarding the energetic factor, the sexual division of tasks may be explained as an adaptation to acquire the skills needed to undertake the complex activities required during adulthood as early as possible. Carrying out gathering activities during childhood and adolescence could be favored by the growth and development cycles of Homo sapiens. Moreover, if most of the energetic costs of gathering activities depend on body mass, the delayed growth in humans relative to other primates allows subadults to practice these tasks for longer periods, and to become better at performing them. In fact, this strategy could enable them to acquire adults' complex skills at a low energetic cost that can be easily subsidized by other members of the group.

Evidence of habitual behavior from non-alimentary dental wear on deciduous teeth from the Middle and Upper Paleolithic Cantabrian region, Northern Spain

The use of 'teeth as tools' (non-masticatory or cultural-related dental wear) has largely been employed as a proxy for studying of past human behavior, mainly in permanent dentition from adult individuals. Here we present the analysis of the non-masticatory dental wear modifications on the deciduous dentition assigned to eight Neanderthal and anatomically modern human subadult individuals from Mousterian to Magdalenian technocultural contexts in the Cantabrian region (Northern Spain). Although preliminary, we tentatively suggest that these eight subadults present activity-related dental wear, including cultural striations, chipped enamel, toothpick grooves, and subvertical grooves. We also found evidence of habitual dental hygienic practices in the form of toothpicking on a deciduous premolar. Orientation of the cultural striations indicates similar handedness development as in modern children. Taken together, these dental wear patterns support the participation of young individuals in group activities, making them potential contributors to group welfare. This study potentially adds new evidence to the importance of the use of the mouth in paramasticatory activities or as a third hand throughout the Pleistocene, which can be confirmed with a more specific reference sample.

Timing, Initiators, and Causes of Divorce in a Mayangna/Miskito Community in Nicaragua

There exists a paucity of evolution-oriented research focusing on why relationships end, particularly in comparison to the substantial literature centered around individual preferences that define the beginning of relationships. In contrast, there is a long tradition in the fields of sociology and family studies of exploring divorce; however, this body of research is largely limited to studies of Western populations. We address these gaps in the literature with an examination of patterns of divorce among a small-scale horticultural population in Nicaragua. We test a number of hypotheses derived from behavioral ecology perspective regarding the timing and causes of divorce. Results lend support to all but one of the hypotheses. Overall divorce rates are comparable to U.S. rates; however, they tend to occur earlier in marriages. Children appear to provide a slight buffering effect against divorce, although age in marriage does not. Gender differences in the reported causes of divorce fall along the lines that would be expected due to differences in partner preferences reported in previous research. Finally, this population also exhibits a similar peculiar pattern exhibited by Western populations, in which divorce is more costly for women, and yet women are slightly more likely to initiate divorces than husbands.

Pelvic and neonatal size correlations in light of evolutionary hypotheses

OBJECTIVE

This study aimed to analyze the correlations between maternal size, neonatal size, and gestational variables.

METHODS

Our sample comprises 131 mother-infant dyads. We investigated correlations between five neonatal traits (gestational age, birthweight, head, suboccipito-brematic, and abdominal girths), three maternal traits (height, BMI, and uterus height), and three pelvic variables (conjugate, inter-spinous diameters, and sub-pubic angle) using computed tomography pelvimetry.

RESULTS

We found that the five neonatal traits were significantly intercorrelated. BMI was not correlated with neonatal traits while maternal height was correlated with birthweight, suboccipito-brematic, and abdominal girth. In the multiple regression models, gestational age was correlated with birthweight, head, and abdominal girth. Among the neonatal and pelvimetry correlations, conjugate diameter was slightly correlated with suboccipito-bregmatic girth, but inter-spinous and sub-pubic angle were not correlated with neonatal traits. Uterus height predicted all neonatal variables, but it was not correlated with gestational age.

DISCUSSION

Our results suggest that fetal growth is shaped by maternal phenotype rather than external ecological factors. The association of the inlet size with suboccipito-bregmatic girth reflects the tight fit between the neonatal brain and the maternal pelvis dimensions, an adaptation that would reduce the risk of cephalo-pelvic disproportion, while the absence of tight fit at the midplane and outlet could be due to the effect of the pelvic relaxation. Uterus distention is not the only mechanism involved in the initiation of parturition. Birth and pregnancy are complex processes and we suggest that maternal-neonatal associations are the result of a combination of multiple obstetric tradeoffs.

Mother’s Partnership Status and Allomothering Networks in the United Kingdom and United States

In high-income, low-fertility (HILF) settings, the mother’s partner is a key provider of childcare. However, it is not clear how mothers without partners draw on other sources of support to raise children. This paper reports the findings from a survey of 1532 women in the United Kingdom and the United States, in which women described who provided childcare for a focal child and how frequently they did so. We use multivariate Bayesian regression models to explore the drivers of support from partners, maternal kin, and other allomothers, as well as the potential impact of allomothering on women’s fertility. Relative to mothers who are in a stable first marriage or cohabitation, mothers who are unpartnered rely more heavily on fewer maternal kin, use more paid help, and have networks which include more non-kin helpers. Repartnered mothers received less help from their partners in the UK and less help from maternal kin in both countries, which US mothers compensated for by relying on other helpers. While repartnered mothers had higher age-adjusted fertility than women in a first partnership, allomaternal support was not clearly related to the mother’s fertility. These findings demonstrate the importance of partners but also of allomothering more broadly in HILF settings.

The Life History of Learning Subsistence Skills among Hadza and BaYaka Foragers from Tanzania and the Republic of Congo

Aspects of human life history and cognition, such as our long childhoods and extensive use of teaching, theoretically evolved to facilitate the acquisition of complex tasks. The present paper empirically examines the relationship between subsistence task difficulty and age of acquisition, rates of teaching, and rates of oblique transmission among Hadza and BaYaka foragers from Tanzania and the Republic of Congo. We further examine cross-cultural variation in how and from whom learning occurred. Learning patterns and community perceptions of task difficulty were assessed through interviews. We found no relationship between task difficulty, age of acquisition, and oblique transmission, and a weak but positive relationship between task difficulty and rates of teaching. While same-sex transmission was normative in both societies, tasks ranked as more difficult were more likely to be transmitted by men among the BaYaka, but not among the Hadza, potentially reflecting cross-cultural differences in the sexual division of subsistence and teaching labor. Further, the BaYaka were more likely to report learning via teaching, and less likely to report learning via observation, than the Hadza, possibly owing to differences in socialization practices.

Children and innovation: play, play objects and object play in cultural evolution

Cultural evolutionary theory conceptualises culture as an information-transmission system whose dynamics take on evolutionary properties. Within this framework, however, innovation has been likened to random mutations, reducing its occurrence to chance or fortuitous transmission error. In introducing the special collection on children and innovation, we here place object play and play objects - especially functional miniatures - from carefully chosen archaeological contexts in a niche construction perspective. Given that play, including object play, is ubiquitous in human societies, we suggest that plaything construction, provisioning and use have, over evolutionary timescales, paid substantial selective dividends via ontogenetic niche modification. Combining findings from cognitive science, ethology and ethnography with insights into hominin early developmental life-history, we show how play objects and object play probably had decisive roles in the emergence of innovative capabilities. Importantly, we argue that closer attention to play objects can go some way towards addressing changes in innovation rates that occurred throughout human biocultural evolution and why innovations are observable within certain technological domains but not others.

The Brain Emotional Systems in Addictions: From Attachment to Dominance/Submission Systems

Human development has become particularly complex during the evolution. In this complexity, adolescence is an extremely important developmental stage. Adolescence is characterized by biological and social changes that create the prerequisites to psychopathological problems, including both substance and non-substance addictive behaviors. Central to the dynamics of the biological changes during adolescence are the synergy between sexual and neurophysiological development, which activates the motivational/emotional systems of Dominance/Submission. The latter are characterized by the interaction between the sexual hormones, the dopaminergic system and the stress axis (HPA). The maturation of these motivational/emotional systems requires the integration with the phylogenetically more recent Attachment/CARE Systems, which primarily have governed the subject's relationships until puberty. The integration of these systems is particularly complex in the human species, due to the evolution of the process of competition related to sexual selection: from a simple fight between two individuals (of the same genus and species) to a struggle for the acquisition of a position in rank and the competition between groups. The latter is an important evolutionary acquisition and believed to be the variable that has most contributed to enhancing the capacity for cooperation in the human species. The interaction between competition and cooperation, and between competition and attachment, characterizes the entire human relational and emotional structure and the unending work of integration to which the BrainMind is involved. The beginning of the integration of the aforementioned motivational/emotional systems is currently identified in the prepubertal period, during the juvenile stage, with the development of the Adrenarche-the so-called Adrenal Puberty. This latter stage is characterized by a low rate of release of androgens, the hormones released by the adrenal cortex, which activate the same behaviors as those observed in the PLAY system. The Adrenarche and the PLAY system are biological and functional prerequisites of adolescence, a period devoted to learning the difficult task of integrating the phylogenetically ancient Dominance/Submission Systems with the newer Attachment/CARE Systems. These systems accompany very different adaptive goals which can easily give rise to mutual conflict and can in turn make the balance of the BrainMind precarious and vulnerable to mental suffering.

Molecules, Mechanisms, and Disorders of Self-Domestication: Keys for Understanding Emotional and Social Communication from an Evolutionary Perspective

The neural crest hypothesis states that the phenotypic features of the domestication syndrome are due to a reduced number or disruption of neural crest cells (NCCs) migration, as these cells differentiate at their final destinations and proliferate into different tissues whose activity is reduced by domestication. Comparing the phenotypic characteristics of modern and prehistoric man, it is clear that during their recent evolutionary past, humans also went through a process of self-domestication with a simultaneous prolongation of the period of socialization. This has led to the development of social abilities and skills, especially language, as well as neoteny. Disorders of neural crest cell development and migration lead to many different conditions such as Waardenburg syndrome, Hirschsprung disease, fetal alcohol syndrome, DiGeorge and Treacher-Collins syndrome, for which the mechanisms are already relatively well-known. However, for others, such as Williams-Beuren syndrome and schizophrenia that have the characteristics of hyperdomestication, and autism spectrum disorders, and 7dupASD syndrome that have the characteristics of hypodomestication, much less is known. Thus, deciphering the biological determinants of disordered self-domestication has great potential for elucidating the normal and disturbed ontogenesis of humans, as well as for the understanding of evolution of mammals in general.

DHEAS and Human Development: An Evolutionary Perspective

Adrenarche, the post-natal rise of DHEA and DHEAS, is unique to humans and the African Apes. Recent findings have linked DHEA in humans to the development of the left dorsolateral prefrontal cortex (LDPFC) between the ages of 4-8 years and the right temporoparietal junction (rTPJ) from 7 to 12 years of age. Given the association of the LDLPFC with the 5-to-8 transition and the rTPJ with mentalizing during middle childhood DHEA may have played an important role in the evolution of the human brain. I argue that increasing protein in the diet over the course of human evolution not only increased levels of DHEAS, but linked meat consumption with brain development during the important 5- to-8 transition. Consumption of animal protein has been associated with IGF-1, implicated in the development of the adrenal zona reticularis (ZR), the site of DHEAS production. In humans and chimps, the zona reticularis emerges at 3-4 years, along with the onset of DHEA/S production. For chimps this coincides with weaning and peak synaptogenesis. Among humans, weaning is completed around 2 ½ years, while synaptogenesis peaks around 5 years. Thus, in chimpanzees, early cortical maturation is tied to the mother; in humans it may be associated with post-weaning provisioning by others. I call for further research on adrenarche among the African apes as a critical comparison to humans. I also suggest research in subsistence populations to establish the role of nutrition and energetics in the timing of adrenarche and the onset of middle childhood.

Life history changes accompany increased numbers of cortical neurons: A new framework for understanding human brain evolution

Narratives of human evolution have focused on cortical expansion and increases in brain size relative to body size, but considered that changes in life history, such as in age at sexual maturity and thus the extent of childhood and maternal dependence, or maximal longevity, are evolved features that appeared as consequences of selection for increased brain size, or increased cognitive abilities that decrease mortality rates, or due to selection for grandmotherly contribution to feeding the young. Here I build on my recent finding that slower life histories universally accompany increased numbers of cortical neurons across warm-blooded species to propose a simpler framework for human evolution: that slower development to sexual maturity and increased post-maturity longevity are features that do not require selection, but rather inevitably and immediately accompany evolutionary increases in numbers of cortical neurons, thus fostering human social interactions and cultural and technological evolution as generational overlap increases.

Opportunistic feeding strategy in wild immature chimpanzees: Implications for children as active foragers in human evolution

Modern human (Homo sapiens) children are generally considered to be dependent on older individuals for foods, even after weaning. However, recent studies of hunter-gatherer societies have reported that children can also acquire food by themselves, although the degree of self-provisioning by children differs among groups and is considered a facultative adaptation. To investigate the dependence of children on older individuals for food and the importance of self-provisioning in early hominins, I examined feeding behavior in wild, immature chimpanzees (Pan troglodytes schweinfurthii). I studied 19 mother-offspring chimpanzee pairs in the Mahale Mountains National Park, Tanzania for approximately 22 months. Feeding behavior and interactions between mothers and their offspring were recorded. The results supported these three predictions: (1) immature chimpanzees need to feed more frequently than mothers because of increased basal metabolic rate and immature stomach capacity; (2) mothers provide effective opportunities to feed on high-quality food items which are similar to those of the mothers'; and (3) when feeding independently of their mothers, immature chimpanzees consume highly accessible food including non-adult foods nearby mothers to avoid getting lost and physical burden as with self-provisioning of human children in hunter gatherer societies. During non-simultaneous feeding bouts, immature individuals frequently consumed pith and wood. They may be valuable food items for immature individuals during their growth stage because they can be consumed year round and contain relatively higher crude ash and protein amounts, which may enable immature chimpanzees to manage the confines of their immature bodies, preventing them from matching adult feeding rhythms. This opportunistic feeding strategy is similar to self-provisioning by human children in hunter-gatherer societies. These results suggested that early hominin children performed self-provisioning based on opportunistic feeding strategies, and contributed to their food consumption by snacking in accordance with their metabolic needs and physical confines.

Learning curves and teaching when acquiring nut-cracking in humans and chimpanzees

Humans are considered superior to other species in their tool using skills. However, most of our knowledge about animals comes from observations in artificial conditions with individuals removed from their natural environment. We present a first comparison of humans and chimpanzees spontaneously acquiring the same technique as they forage in their natural environment. We compared the acquisition of the Panda nut-cracking technique between Mbendjele foragers from the Republic of Congo and the Taï chimpanzees from Côte d'Ivoire. Both species initially acquire the technique slowly with similar kinds of mistakes, with years of practice required for the apprentice to become expert. Chimpanzees more rapidly acquired the technique when an apprentice, and reached adult efficiency earlier than humans. Adult efficiencies in both species did not differ significantly. Expert-apprentice interactions showed many similar instances of teaching in both species, with more variability in humans due, in part to their more complex technique. While in humans, teaching occurred both vertically and obliquely, only the former existed in chimpanzees. This comparison of the acquisition of a natural technique clarifies how the two species differed in their technical intelligence. Furthermore, our observations support the idea of teaching in both species being more frequent for difficult skills.

First systematic assessment of dental growth and development in an archaic hominin (genus, Homo) from East Asia

Several human dental traits typical of modern humans appear to be associated with the prolonged period of development that is a key human attribute. Understanding when, and in which early hominins, these dental traits first appeared is thus of strong interest. Using x-ray multiresolution synchrotron phase-contrast microtomography, we quantify dental growth and development in an archaic Homo juvenile from the Xujiayao site in northern China dating to 161,000-224,000 years or 104,000-125,000 years before present. Despite the archaic morphology of Xujiayao hominins, most aspects of dental development of this juvenile fall within modern human ranges (e.g., prolonged crown formation time and delayed first molar eruption). For its estimated age-at-death (6.5 years), its state of dental development is comparable to that of equivalently aged modern children. These findings suggest that several facets of modern human dental growth and development evolved in East Asia before the appearance of fully modern human morphology.

How Has the Lower Boundary of Human Mortality Evolved, and Has It Already Stopped Decreasing?

In contrast to the upper boundary of mortality, the lower boundary has so far largely been neglected. Based on the three key features-location, sex-specific difference, and level-I analyze past and present trends in the lower boundary of human mortality. The analysis is based on cohort mortality data for 38 countries, covering all the cohorts born between 1900 and 1993. Minimum mortality is analyzed using observed as well as smoothed estimates. The results show that the ages at which minimum mortality is reached have shifted to lower ages. Although the differences have become almost negligible over time, males are showing higher levels of minimum mortality than females. The level of minimum mortality was halved more than five times over the analyzed time horizon. The results also suggest that even after more than 150 years of mortality improvements, minimum mortality has not yet reached a lowest limit and is likely to decrease further in the near future. Trends in the three key features also raise questions about the importance of evolutionary, social, and biological determinants for the recent and future development of minimum mortality.

Hormones and Human and Nonhuman Primate Growth

The aim of this paper was to review information pertaining to the hormonal regulation of nonhuman primate growth, with specific focus on the growth hormone (GH)-insulin-like growth factor (IGF) axis and adrenal androgens. Hormones of the GH-IGF axis are consistently associated with measures of growth - linear, weight, or both - during the growth period; in adulthood, concentrations of IGF-I, IGF-binding protein-3, and GH-binding protein are not associated with any measures of size. Comparing patterns of dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) may be especially relevant for understanding whether the childhood stage of growth and development is unique to humans and perhaps other apes. Genetic, hormonal, and morphological data on adrenarche in other nonhuman primate species suggest that this endocrine transition is delayed in humans, chimpanzees, and possibly gorillas, while present very early in postnatal life in macaques. This suggests that although perhaps permitted by an extension of the pre-adolescent growth period, childhood builds upon existing developmental substrates rather than having been inserted de novo into an ancestral growth trajectory. Hormones can provide insight regarding the evolution of the human growth trajectory.

The tempo of human childhood: a maternal foot on the accelerator, a paternal foot on the brake

Relative to the life history of other great apes, that of humans is characterized by early weaning and short interbirth intervals (IBIs). We propose that in modern humans, birth until adrenarche, or the rise in adrenal androgens, developmentally corresponds to the period from birth until weaning in great apes and ancestral hominins. According to this hypothesis, humans achieved short IBIs by subdividing ancestral infancy into a nurseling phase, during which offspring fed at the breast, and a weanling phase, during which offspring fed specially prepared foods. Imprinted genes influence the timing of human weaning and adrenarche, with paternally expressed genes promoting delays in childhood maturation and maternally expressed genes promoting accelerated maturation. These observations suggest that the tempo of human development has been shaped by consequences for the fitness of kin, with faster development increasing maternal fitness at a cost to child fitness. The effects of imprinted genes suggest that the duration of the juvenile period (adrenarche until puberty) has also been shaped by evolutionary conflicts within the family.

The role of play objects and object play in human cognitive evolution and innovation

In this contribution, we address a major puzzle in the evolution of human material culture: If maturing individuals just learn their parental generation's material culture, then what is the origin of key innovations as documented in the archeological record? We approach this question by coupling a life‐history model of the costs and benefits of experimentation with a niche‐construction perspective. Niche‐construction theory suggests that the behavior of organisms and their modification of the world around them have important evolutionary ramifications by altering developmental settings and selection pressures. Part of Homo sapiens' niche is the active provisioning of children with play objects — sometimes functional miniatures of adult tools — and the encouragement of object play, such as playful knapping with stones. Our model suggests that salient material culture innovation may occur or be primed in a late childhood or adolescence sweet spot when cognitive and physical abilities are sufficiently mature but before the full onset of the concerns and costs associated with reproduction. We evaluate the model against a series of archeological cases and make suggestions for future research.

The enigmatic relationship between epiphyseal fusion and bone development in primates

Epiphyseal fusion in primates is a process that occurs in a regular sequence spanning a period of years and thus provides biological anthropologists with a useful marker of maturity that can be used to assess age and stage of development. Despite the many studies that have catalogued fusion timing and sequence pattern, comparatively little research has been devoted to understanding why these sequences exist in the first place. Answering this question is not necessarily intuitive; indeed, given that neither taxonomic affinities nor recent adaptations have been clearly defined, it is a challenge to explain this process in evolutionary terms. In all mammals, there is a tendency for the fusion of epiphyses at joints to occur close in sequence, and this has been proposed to relate to locomotor adaptations. Further consideration of the evidence suggests that linking locomotor behavior to sequence data alone is difficult to prove and may require a different type of evidence. Epiphyseal fusion should be considered in the context of other parameters that affect the developing skeleton, including how joint morphology relates to growth in length, as well as other possible morphological constraints. In recent years, developmental biology has been providing a better understanding of the molecular regulators of epiphyseal fusion. At some point in the near future, we may be able to link our understanding of the genetics of fusion timing to the possible selective mechanisms that are responsible for these sequences.

How Do Hunter-Gatherer Children Learn Subsistence Skills? : A Meta-Ethnographic Review

Hunting and gathering is, evolutionarily, the defining subsistence strategy of our species. Studying how children learn foraging skills can, therefore, provide us with key data to test theories about the evolution of human life history, cognition, and social behavior. Modern foragers, with their vast cultural and environmental diversity, have mostly been studied individually. However, cross-cultural studies allow us to extrapolate forager-wide trends in how, when, and from whom hunter-gatherer children learn their subsistence skills. We perform a meta-ethnography, which allows us to systematically extract, summarize, and compare both quantitative and qualitative literature. We found 58 publications focusing on learning subsistence skills. Learning begins early in infancy, when parents take children on foraging expeditions and give them toy versions of tools. In early and middle childhood, children transition into the multi-age playgroup, where they learn skills through play, observation, and participation. By the end of middle childhood, most children are proficient food collectors. However, it is not until adolescence that adults (not necessarily parents) begin directly teaching children complex skills such as hunting and complex tool manufacture. Adolescents seek to learn innovations from adults, but they themselves do not innovate. These findings support predictive models that find social learning should occur before individual learning. Furthermore, these results show that teaching does indeed exist in hunter-gatherer societies. And, finally, though children are competent foragers by late childhood, learning to extract more complex resources, such as hunting large game, takes a lifetime.

Maturation is prolonged and variable in female chimpanzees

Chimpanzees are important referential models for the study of life history in hominin evolution. Age at sexual maturity and first reproduction are key life history milestones that mark the diversion of energy from growth to reproduction and are essential in comparing life history trajectories between chimpanzees and humans. Yet, accurate information on ages at these milestones in wild chimpanzees is difficult to obtain because most females transfer before breeding. Precise age at first birth is only known from a relatively small number of non-dispersing individuals. Moreover, due to small sample sizes, the degree to which age at maturation milestones varies is unknown. Here we report maturation milestones and explore sources of variance for 36 wild female chimpanzees of known age, including eight dispersing females born in Gombe National Park, Tanzania. Using Kaplan-Meier survival analysis, including censored intervals, we find an average age of 11.5 years (range 8.5-13.9) at sexual maturity and 14.9 years (range 11.1-22.1) at first birth. These values exceed previously published averages for wild chimpanzees by one or more years. Even in this larger sample, age at first birth is likely underestimated due to the disproportionate number of non-dispersing females, which, on average, give birth two years earlier than dispersing females. Model selection using Cox Proportional Hazards models shows that age at sexual maturity is delayed in females orphaned before age eight years and those born to low-ranking mothers. Age at first birth is most delayed in dispersing females and those orphaned before age eight years. These data provide improved estimates of maturation milestones in a population of wild female chimpanzees and indicate the importance of maternal factors in development.

Life History theory hypotheses on child growth: Potential implications for short and long-term child growth, development and health

Life history theory integrates ecological, physiological, and molecular layers within an evolutionary framework to understand organisms' strategies to optimize survival and reproduction. Two life history hypotheses and their implications for child growth, development, and health (illustrated in the South African context) are reviewed here. One hypothesis suggests that there is an energy trade-off between linear growth and brain growth. Undernutrition in infancy and childhood may trigger adaptive physiological mechanisms prioritizing the brain at the expense of body growth. Another hypothesis is that the period from conception to infancy is a critical window of developmental plasticity of linear growth, the duration of which may vary between and within populations. The transition from infancy to childhood may mark the end of a critical window of opportunity for improving child growth. Both hypotheses emphasize the developmental plasticity of linear growth and the potential determinants of growth variability (including the role of parent-offspring conflict in maternal resources allocation). Implications of these hypotheses in populations with high burdens of undernutrition and infections are discussed. In South Africa, HIV/AIDS during pregnancy (associated with adverse birth outcomes, short duration of breastfeeding, and social consequences) may lead to a shortened window of developmental plasticity of growth. Furthermore, undernutrition and infectious diseases in children living in South Africa, a country undergoing a rapid nutrition transition, may have adverse consequences on individuals' cognitive abilities and risks of cardio-metabolic diseases. Studies are needed to identify physiological mechanisms underlying energy allocation between biological functions and their potential impacts on health.

Post-weaning diet in archaeological human populations: A meta-analysis of carbon and nitrogen stable isotope ratios of child skeletons

OBJECTIVES

Childhood is a unique stage in human life history, in which subadults have completed their weaning process but are still dependent on older individuals for survival. Although the importance of food provisioning during childhood has been intensively discussed, childhood diet in the past has rarely been studied in a systematic manner.

METHODS

In this study, a meta-analysis of carbon and nitrogen stable isotope ratios of post-weaning children (PWC) in Holocene human populations around the world is presented. The isotope ratios of PWC were standardized with those of adult females and males in the same population, and they were analyzed in terms of the difference in subsistence.

RESULTS

Results of this study indicate that diets of PWC and adults were generally similar (most differences were within the range of ±1‰), which is consistent with the universal feature of food provisioning to PWC in humans. In hunter-gatherer populations, there is no significant difference between PWC and adult isotope ratios. In non-hunter-gatherer populations, however, PWC probably consumed significantly larger proportions of foods from lower trophic levels than did the adults, and such foods would be terrestrial C₃ plants.

CONCLUSIONS

Potential factors relating to the dietary differences among PWC and adults are presented from a perspective of balance between food provisioning and self-acquisition by PWC. Significant isotopic differences between PWC and adults in non-hunter-gatherer populations revealed in this study have implications for declined health during the subsistence transition in Holocene, isotopic studies using human tooth enamel, and "δ¹⁵ N dip" of subadults after weaning.

Favorable ecological circumstances promote life expectancy in chimpanzees similar to that of human hunter-gatherers

Demographic data on wild chimpanzees are crucial for understanding the evolution of chimpanzee and hominin life histories, but most data come from populations affected by disease outbreaks and anthropogenic disturbance. We present survivorship data from a relatively undisturbed and exceptionally large community of eastern chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. We monitored births, deaths, immigrations, and emigrations in the community between 1995 and 2016. Using known and estimated ages, we calculated survivorship curves for the whole community, for males and females separately, and for individuals ≤2 years old when identified. We used a novel method to address age estimation error by calculating stochastic survivorship curves. We compared Ngogo life expectancy, survivorship, and mortality rates to those from other chimpanzee communities and human hunter-gatherers. Life expectancy at birth for both sexes combined was 32.8 years, far exceeding estimates of chimpanzee life expectancy in other communities, and falling within the range of human hunter-gatherers (i.e., 27-37 years). Overall, the pattern of survivorship at Ngogo was more similar to that of human hunter-gatherers than to other chimpanzee communities. Maximum lifespan for the Ngogo chimpanzees, however, was similar to that reported at other chimpanzee research sites and was less than that of human-hunter gatherers. The absence of predation by large carnivores may contribute to some of the higher survivorship at Ngogo, but this cannot explain the much higher survivorship at Ngogo than at Kanyawara, another chimpanzee community in the same forest, which also lacks large carnivores. Higher survivorship at Ngogo appears to be an adaptive response to a food supply that is more abundant and varies less than that of Kanyawara. Future analyses of hominin life history evolution should take these results into account.

Explanations for attractiveness-related positive biases in an evolutionary perspective of life history theory

The mating-related evolutionary explanation that Maestripieri et al. offer does not apply to (1) infants' positive biases toward attractive individuals and (2) adults' positive biases toward attractive infants and children. They are best understood when integrated into an evolutionary life history framework. I argue that the life history of positive biases toward attractive individuals is driven by fundamental trade-offs made throughout development.

Imitative and Direct Learning as Interacting Factors in Life History Evolution

The idea that lifetime learning can have a significant effect on life history evolution has recently been explored using a series of artificial life simulations. These involved populations of competing individuals evolving by natural selection to learn to perform well on simplified abstract tasks, with the learning consisting of identifying regularities in their environment. In reality, there is more to learning than that type of direct individual experience, because it often includes a substantial degree of social learning that involves various forms of imitation of what other individuals have learned before them. This article rectifies that omission by incorporating memes and imitative learning into revised versions of the previous approach. To do this reliably requires formulating and testing a general framework for meme-based simulations that will enable more complete investigations of learning as a factor in any life history evolution scenarios. It does that by simulating imitative information transfer in terms of memes being passed between individuals, and developing a process for merging that information with the (possibly inconsistent) information acquired by direct experience, leading to a consistent overall body of learning. The proposed framework is tested on a range of learning variations and a representative set of life history factors to confirm the robustness of the approach. The simulations presented illustrate the types of interactions and tradeoffs that can emerge, and indicate the kinds of species-specific models that could be developed with this approach in the future.