Home Birth Midwifery in the United States

Human childbirth is distinct in requiring—or at least strongly profiting from—the assistance of a knowledgeable attendant to support the mother during birth. With economic modernization, the role of that attendant is transformed, and increased access to obstetric interventions may bring biomedicine into conflict with anatomical, physiological, and behavioral adaptations for childbirth. This article provides an overview of the role of midwifery in human evolution and ways in which this evolutionary heritage is reflected in home birth in the contemporary United States. Opportunities remain for evolutionary scholars to apply their knowledge and skills to strengthen culturally consonant, evolutionarily grounded maternity care within a complex, multilevel, pluralistic medical system.     

There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form

Compared to other primates, modern humans face high rates of maternal and neonatal morbidity and mortality during childbirth. Since the early 20th century, this “difficulty” of human parturition has prompted numerous evolutionary explanations, typically assuming antagonistic selective forces acting on maternal and fetal traits, which has been termed the “obstetrical dilemma.” Recently, there has been a growing tendency among some anthropologists to question the difficulty of human childbirth and its evolutionary origin in an antagonistic selective regime. Partly, this stems from the motivation to combat increasing pathologization and overmedicalization of childbirth in industrialized countries. Some authors have argued that there is no obstetrical dilemma at all, and that the difficulty of childbirth mainly results from modern lifestyles and inappropriate and patriarchal obstetric practices. The failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions is sometimes interpreted as empirical support for discarding an obstetrical dilemma. Here we explain why these points are important but do not invalidate evolutionary explanations of human childbirth. We present robust empirical evidence and solid evolutionary theory supporting an obstetrical dilemma, yet one that is much more complex than originally conceived in the 20th century. We argue that evolutionary research does not hinder appropriate midwifery and obstetric care, nor does it promote negative views of female bodies. Understanding the evolutionary entanglement of biological and sociocultural factors underlying human childbirth can help us to understand individual variation in the risk factors of obstructed labor, and thus can contribute to more individualized maternal care.     

The multifactor pelvis: An alternative to the adaptationist approach of the obstetrical dilemma

The obstetrical dilemma describes the competing demands that a bipedally adapted pelvis and a large-brained neonate place on human childbirth and is the predominant model within which hypotheses about the evolution of the pelvis are framed. I argue the obstetrical dilemma follows the adaptationist program outlined by Gould and Lewontin in 1979 and should be replaced with a new model, the multifactor pelvis. This change will allow thorough consideration of nonadaptive explanations for the evolution of the human pelvis and avoid negative social impacts from considering human childbirth inherently dangerous. First, the atomization of the pelvis into discrete traits is discussed, after which current evidence for both adaptive and nonadaptive hypotheses is evaluated, including childbirth, locomotion, shared genetics with other traits under selection, evolutionary history, genetic drift, and environmental and epigenetic influences on the pelvis.     

Psychiatric symptoms following attempted natural childbirth.

As natural childbirth has become more popular, new prenatal training groups have developed, some of which are committed to only one method of dealing with labour and delivery. This paper describes five women and four men who sought psychiatric treatment within 6 months of attempted natural childbirth that did not proceed as planned. Their symptoms included depression, anxiety, obsessive-compulsive behaviour, phobic symptoms, and marital and sexual problems. Thus, natural childbirth, although undoubtedly beneficial in most instances, is not suitable for all deliveries and may occasionally have adverse effects. Prenatal programs should emphasize an individual, flexible approach to labour and delivery and should present the possibility of the need for analgesia, anesthesia or obstetric intervention in a positive light.     

Do human ‘life history strategies’ exist?

Interest in incorporating life history research from evolutionary biology into the human sciences has grown rapidly in recent years. Two core features of this research have the potential to prove valuable in strengthening theoretical frameworks in the health and social sciences: the idea that there is a fundamental trade-off between reproduction and health; and that environmental influences are important in determining how life histories develop. However, the literature on human life histories has increasingly travelled away from its origins in biology, and become conceptually diverse. For example, there are differences of opinion between evolutionary researchers about the extent to which behavioural traits associate with life history traits to form ‘life history strategies’. Here, I review the different approaches to human life histories from evolutionary anthropologists, developmental psychologists and personality psychologists, in order to assess the evidence for human ‘life history strategies’. While there is precedent in biology for the argument that some behavioural traits, notably risk-taking behaviour, may be linked in predictable ways with life history traits, there is little theoretical or empirical justification for including a very wide range of behavioural traits in a ‘life history strategy’. Given the potential of life history approaches to provide a powerful theoretical framework for understanding human health and behaviour, I then recommend productive ways forward for the field: 1) greater focus on the life history trade-offs which underlie proposed strategies; 2) greater precision when using the language of life history theory and life history strategies; 3) collecting more empirical data, from a diverse range of populations, on linkages between life history traits, behavioural traits and the environment, including the underlying mechanisms which generate these linkages; and 4) greater integration with the social and health sciences.     

The effect of development on the direction of evolution: toward a twenty-first century consensus

Summary One of the most important questions in evolutionary biology is: what orients the evolutionary process? That is, what causes evolution to proceed toward certain developmental trajectories, and hence phenotypes, rather than others? In particular, there has been prolonged controversy over whether the direction of evolution is determined solely by external factors or whether the nature of the ontogenetic process, and the ways in which it can be altered by mutations in developmental genes, may also play a major role. Here, I examine this issue, concentrating on the following: the possible evolutionary orienting role of “developmental bias;” the question of whether selection can and/or will break bias; the extent to which bias is already incorporated in quantitative genetic studies; and ways of approaching the possible role of bias in the origin of evolutionary novelties. Finally, I suggest that developmental bias may provide a focal point for the coming together of conceptual and practical approaches to evo‐devo.     

Post-traumatic stress disorder after childbirth: the phenomenon of traumatic birth

CHILDBIRTH CAN BE A VERY PAINFUL EXPERIENCE, often associated with feelings of being out of control. It should not, therefore, be surprising that childbirth may be traumatic for some women. Most women recover quickly post partum; others appear to have a more difficult time. The author asserts that post-traumatic stress disorder (PTSD) may occur after childbirth. He calls this variant of PTSD a "traumatic birth experience." There is very little literature on this topic. The evidence available is from case series, qualitative research and studies of women seeking elective cesarean section for psychologic reasons. Elective cesarean section exemplifies the avoidance behaviour typical of PTSD. There are many ways that health care professionals, including physicians, obstetric nurses, midwives, psychologists, psychiatrists and social workers, can address this phenomenon. These include taking a careful history to determine whether a woman has experienced trauma that could place her at risk for a traumatic birth experience; providing excellent pain control during childbirth and careful postpartum care that includes understanding the woman''s birth experience; and ruling out postpartum depression. Much more research is needed in this area.     

Obstetric violence as immigration injustice: A view from the United States and Colombia

In September 2020, Project South, along with numerous other organizations, released a report detailing abuses in a Georgia Detention Center – including forced hysterectomies. Whatever other factors are at play, one of them is an intrinsic connection between obstetric violence against pregnant migrants and immigration injustice. It is not incidental that these acts – in US detention centers, along the US-Mexico border, in Colombian hospitals and clinics – are being perpetrated on immigrant bodies. And it is not accidental or random which immigrant bodies are vulnerable to these violations. Understanding and confronting obstetric violence directed at pregnant migrants, though, requires reconceptualizing the nature of obstetric violence itself. In particular, we must recognize that obstetric violence against pregnant Latin American migrants in the United States and Colombia is a type of immigration injustice, a means to perpetrate immigration injustice, and a product of immigration injustice. As such, bioethicists need to collaborate with immigration scholars to resist it. After providing some background on the nature of obstetric violence and some ways it is perpetuated against pregnant migrants in the United States and Colombia, I will give a brief overview of how I conceptualize immigration justice. From there, I explain how this type of obstetric violence constitutes a type of immigration injustice, a means to perpetrate immigration injustice, and a product of immigration injustice. My hope is that this analysis motivates bioethicists throughout the Americas to engage with immigration scholars and activists to confront the issue more forcefully.     

Sex,gender, and difference

Empirical research has demonstrated that women’s aggressive behavior is widespread and displays regularities across societies. Until recently, however, discussions about the aggressive behavior of women and gender differences in aggressive behavior have been based largely on data from nonhuman primates, children, or laboratory experiments. Using a unique corpus of naturalistic data on aggressive human interactions both between and among men and women, I explore the complexity of our questions about sex differences in aggression and further illuminate the ways in which men and women may use aggression in human interactions. In this paper I compare the aggressive behavior of men and women in an Australian Aboriginal community. In doing so I argue for the continuing use of a “sex differences” framework for organizing our understanding of gender relations and gender hierarchy. I believe, however, that this form of analysis benefits from, if not requires, a sensitivity to the most taken-for-granted aspects of our gender ideology and a commitment to attend to evidence that challenges our convictions about men and women.     

Parasites and human evolution

Our understanding of human evolutionary and population history can be advanced by ecological and evolutionary studies of our parasites. Many parasites flourish only in the presence of very specific human behaviors and in specific habitats, are wholly dependent on us, and have evolved with us for thousands or millions of years. Therefore, by asking when and how we first acquired those parasites, under which environmental and cultural conditions we are the most susceptible, and how the parasites have evolved and adapted to us and we in response to them, we can gain considerable insight into our own evolutionary history. 1 , 2 As examples, the tapeworm life cycle is dependent on our consumption of meat,³ the divergence of body and head lice may have been subsequent to the development of clothing, 4 , 5 and malaria hyperendemicity may be associated with agriculture. 6 Thus, the evolutionary and population histories of these parasites are likely intertwined with critical aspects of human biology and culture. Here I review the mechanics of these and multiple other parasite proxies for human evolutionary history and discuss how they currently complement our fossil, archeological, molecular, linguistic, historical, and ethnographic records. I also highlight potential future applications of this promising model for the field of evolutionary anthropology.     

The single active X in human cells: evolutionary tinkering personified

All mammals compensate for sex differences in numbers of X chromosomes by transcribing only a single X chromosome in cells of both sexes; however, they differ from one another in the details of the compensatory mechanisms. These species variations result from chance mutations, species differences in the staging of developmental events, and interactions between events that occur concurrently. Such variations, which have only recently been appreciated, do not interfere with the strategy of establishing a single active X, but they influence how it is carried out. In an overview of X dosage compensation in human cells, I point out the evolutionary variations. I also argue that it is the single active X that is chosen, rather than inactive ones. Further, I suggest that the initial events in the process—those that precede silencing of future inactive X chromosomes—include randomly choosing the future active X, most likely by repressing its XIST locus.     

Impact of non-indigenous species on natives enhanced by anthropogenic alteration of selection regimes

Changes in environmental conditions often reverse outcomes of competitive interactions among species. Such context dependency implies that the speed, persistence, and ubiquity of anthropogenic habitat alterations may suddenly put even previously well-adapted native species at a competitive disadvantage with non-native species. That is, anthropogenic disturbance may so drastically alter environments that a native species finds itself in an environment that in key ways is just as novel as it is to a non-indigenous species. Extreme disturbances may thereby erase a native species' prior advantage of local environmental adaptation accrued during its long-term incumbency over evolutionary time. I document examples from two areas of dramatic human alteration of selection regimes – eutrophication and the selective removal of top predators – that support this mechanism. Additionally, I highlight ways in which this mechanism is experimentally testable. Alteration of selection regimes may prove to be a powerful explanation for the enhanced success and impact of biological invasions in our globally disturbed biosphere.     

The Replicator in Retrospect

The history and theoretical role of the concept of a ``replicator'is discussed, starting with Dawkins' and Hull's classic treatmentsand working forward. I argue that the replicator concept is still auseful one for evolutionary theory, but it should be revised insome ways. The most important revision is the recognition that notall processes of evolution by natural selection require thatsomething play the role of a replicator.     

Evolution of heterogeneous perceptual limits and indifference in competitive foraging

The collective behaviour of animal and human groups emerges from the individual decisions and actions of their constituent members. Recent research has revealed many ways in which the behaviour of groups can be influenced by differences amongst their constituent individuals. The existence of individual differences that have implications for collective behaviour raises important questions. How are these differences generated and maintained? Are individual differences driven by exogenous factors, or are they a response to the social dilemmas these groups face? Here I consider the classic case of patch selection by foraging agents under conditions of social competition. I introduce a multilevel model wherein the perceptual sensitivities of agents evolve in response to their foraging success or failure over repeated patch selections. This model reveals a bifurcation in the population, creating a class of agents with no perceptual sensitivity. These agents exploit the social environment to avoid the costs of accurate perception, relying on other agents to make fitness rewards insensitive to the choice of foraging patch. This provides a individual-based evolutionary basis for models incorporating perceptual limits that have been proposed to explain observed deviations from the Ideal Free Distribution (IFD) in empirical studies, while showing that the common assumption in such models that agents share identical sensory limits is likely false. Further analysis of the model shows how agents develop perceptual strategic niches in response to environmental variability. The emergence of agents insensitive to reward differences also has implications for societal resource allocation problems, including the use of financial and prediction markets as mechanisms for aggregating collective wisdom.     

Profile of Numbers of Sequence Differences Among V-Genes Coding for the Variable Regions of T Cell Receptor for Antigen Alpha and Beta Chains

When human T cell receptor for antigen (TCR) alpha chain V-genes were compared pair-wise, the numbers of nucleotide differences showed a characteristic distribution; most were in the range of 100 to 200 differences out of a total of about 300 bases. The same distribution was observed for mouse TCR alpha chains. Even more interesting was that comparing human alpha chains and mouse alpha chains gave essentially the same nucleotide difference pattern. It is inferred from the large number of differences and from the nonspecificity of trans-species (human and mouse) nucleotide sequence differences of TCR V-genes that TCR alpha chains probably diverged early during evolution. The same feature was also observed for human and mouse TCR beta chains, although the alpha and beta chain V-genes were distinct. This evolutionary preservation could be of vital importance to the fidelity of the complicated trimolecular interactions among TCR alpha and beta chains, the processed peptide, and the major histocompatibility complex (MHC) class I or II molecules. Received: 22 January 1996 / Accepted: 9 September 1996     

Long term backache after childbirth: prospective search for causative factors.

OBJECTIVES--To assess in a prospective randomised study the association between motor block resulting from high and low dose epidural infusions of bupivacaine in labour and the incidence of long term backache after childbirth, and to compare the incidence of backache in women not receiving epidural analgesia. DESIGN--Women requesting epidural analgesia in labour between October 1991 and March 1994 were randomised to receive infusions of either bupivacaine alone or low dose bupivacaine with opioid. Data were collected during labour and the immediate postpartum period from these women and from women recruited at random over the same time from those who had laboured without epidural analgesia. A postal questionnaire about symptoms was sent three months after childbirth to all women. Further data were collected one year after childbirth from those who had reported new backache at three months. SETTING--St Thomas''s Hospital, London. SUBJECTS--599 women were recruited, of whom 450 (75%) replied to a follow up questionnaire. RESULTS--152 women (33.8% of responders) reported backache lasting three months after delivery and, of these, 33 (7.3%) had not previously suffered with backache. There were no significant differences between the treatment groups in the incidence of postnatal backache overall or of new backache or any symptoms after childbirth. Among all demographic, obstetric, and epidural variables examined the only factors significantly associated with backache after childbirth were backache before and during pregnancy. CONCLUSIONS--The incidence of new long term backache was not significantly increased in women who received epidural analgesia in labour. Motor block resulting from epidural local anaesthetic administration was not a significant factor in the development of backache.     

Evolutionary biology of language

Language is the most important evolutionary invention of the last few million years. It was an adaptation that helped our species to exchange information, make plans, express new ideas and totally change the appearance of the planet. How human language evolved from animal communication is one of the most challenging questions for evolutionary biology The aim of this paper is to outline the major principles that guided language evolution in terms of mathematical models of evolutionary dynamics and game theory. I will discuss how natural selection can lead to the emergence of arbitrary signs, the formation of words and syntactic communication.     

Developmental perspective on size change and allometry in evolution

The evolution of changes in body size is one of the most important patterns in the history of life. Its importance arises from both the frequency of the pattern and the biological implications of size change itself, which affects myriad aspects of an organism's structure and function through well-known scaling relationships. Yet relatively little attention has been focused on the underlying genetic and developmental controls of size change or their implications with regard to other morphological changes. Here, I review the endocrine growth axis and show that variation in several key growth-control substances, particularly growth hormone (GH) and insulin-like growth factor I (IGF I), is clearly linked to intraspecific differences in postnatal growth rates and terminal body size. I intentionally review a considerable amount of literature on nonprimate mammals because this research is vital to an understanding of the general topic. Research on human pygmies, giant transgenic mice, and other models of growth disturbances indicates that shifts in GH and/or IGF I levels not only yield the expected changes in terminal body size, but also result in simple truncations or extensions of underlying allometric patterns. These data provide a possible developmental basis for the common finding of ontogenetic scaling and coordinated transformations in series of closely related fossil or living species that differ in body size. At present, however, this must be viewed as a hypothesis that requires testing through interspecific analyses. A consideration of previous interpretations of the morphological distinctions of human pygmies and some other organisms demonstrates the novel information that a developmental perspective brings to morphological comparisons. Clearly, knowledge of the genetic and developmental controls of morphogenesis will greatly enhance our understanding of a multitude of evolutionary patterns, processes and mechanisms, for it is perturbations in these these controls that ultimately produce the raw material for evolutionary transformations.