The Role of the Immune System from an Evolutionary Perspective

“Nothing in Biology makes sense, except in the light of evolution.” This famous citation of Theodosius Dobzhansky also underlies the integrative field of evolutionary medicine, which faces the challenge to combine (patho-)physiological mechanisms with evolutionary function. Here we introduce a concept from the study of animal behavior, which are the four questions of Tinbergen that consider: 1. the ontogeny of an individual describing its development, 2. its physiological machinery, which 3. has fitness consequences influencing 4. the evolutionary history (phylogeny) of future generations. It is shown how this concept can be applied to infectious disease and to chronic inflammatory systemic diseases. Evolutionary medicine takes lifetime reproductive success into account. The hypothesis to be tested is that mechanisms underlying a disease in old age might have higher fitness benefits in the pre-reproductive and/or reproductive life history stage, leading to an overall increased lifetime fitness.

An Evolutionary View of Homeostasis

Physiologists and evolutionary biologists have traditionally investigated different but complementary aspects of biological phenomena. Homeostasis, the maintenance of approximately constant conditions in bodily fluids, has been the purview of physiology. Evolutionary insights can, however, deepen our knowledge of homeostatic regulatory mechanisms. Bioenergetics has been of central concern to both physiology and evolution. Physiologists have been interested in the energetic content of foods, in the metabolic transformations of the energy derived from foods, and in the energetic costs of physiological processes, while evolutionary life history theory addresses the ways that organisms have evolved to acquire and allocate metabolic energy throughout their life course. Engineering control theory highlights the limitations as well as the benefits of different regulatory mechanisms and so helps to explain why we have evolved multiple integrated and cooperative homeostatic mechanisms. The physiological responses to pregnancy illustrate the ways in which an evolutionary perspective enriches our understanding of homeostasis.

Tinbergean Approach to Clinical Medicine

Among the most enduring and influential contributions of Nobel Laureate Nikolaas Tinbergen was the introduction of a four-part framework for understanding biological causation. Beyond traditional proximate-mechanistic explanations, Tinbergen asserted, a consideration of both phylogenetic and functional-adaptive perspectives was essential. The application of a framework derived from this Tinbergean structure to human medicine offers a novel approach to the development of theories of causation for high-impact somatic and bio-behavioral disorders. This perspective offers physicians and physicians-in-training an expanded understanding of the nature and origin of human vulnerability to disease. The phylogenetic perspective expands awareness of non-human animals who spontaneously develop the disorder and the functional-adaptive perspective considers what components of vulnerability to disease might have adaptive benefit. Both facilitate the development of novel testable hypotheses.

Optimizing Maternal-Infant Health

In this chapter, we use an evolutionary lens to deepen understanding of maternal and family needs in the early postpartum period so that health care can be more aligned with confronted realities. The discussion is centered around the concept of the 4th trimester, which is the period between birth and the first 3 months postpartum. This framework encourages a holistic understanding of perinatal health by drawing attention to evolved maternal-infant needs. By addressing these ultimate-level contributors to health issues, we can facilitate more effective clinical support, comprehensive research, and a fuller “village” to enable new families to thrive. Core to this approach is the concept of trade-offs between parents and offspring, exemplified by lactation as a prime example of the complexities of dyadic needs and gap between the current culture of health and optimal support.

Introduction

Evolutionary medicine is an integrative discipline, combining the fields of evolutionary biology, experimental research, and clinical medicine. Contributors to the field of evolutionary medicine today come from many schools of study. Anthropologists, biologists, physiologists, and ecologists work alongside historians of science and physician scientists, all of whom are represented in the present volume. A full integration of evolutionary thought into the education of medical students and seasoned physicians has been voiced by most of the field’s contributors. Incorporating an evolutionary perspective into medicine will most likely not change the daily activity of physicians, but it will help guide the thinking and types of questions a physician-scientist should ask, by adding an evolutionary dimension. Our aim for this volume is to support medical education that teaches evolutionary medicine as a seamless component of medical practice, rather than be considered a separate school of thought.

Ecological Rationality and Evolutionary Medicine

A notion of rationality represents a structure that can be used to explain, evaluate, and recommend a certain course of action. Full rationality, independent of context, builds such a structure based on the rules of logic and statistical inference. Ecological rationality, on the other hand, focuses on the interaction between the human mind and the task environment. This chapter argues that ecological rationality can provide an operational framework for evolutionary medicine based on compatible foundational concepts. Risk literacy and numeracy methods developed on the basis of an adaptive toolbox approach constitute effective education tools. An evolutionary approach to medical education facilitates the integration of these accessible and well-retained educational tools for physicians and their patients, and can enrich public health policymaking.

Darwin’s Impact on the Medical Sciences

In early nineteenth century medicine, the concepts of organic evolution and natural selection emerged in different contexts, partly anticipating Darwinian revolution. In particular, the anatomical concept of disease favored the perception that men and animals were very similar from a morphological, physiological and pathological point of view, and that this could indicate a certain degree of kinship between them. The debate around human races and human pathological heredity saw first formulations of the principle of natural selection, even if without a full appraisal of its evolutionary implications. Charles Darwin took many inspirations from these medical theories. The impact of the theory of evolution formulated by him in 1859 was only apparently slight in medicine. It is even possible to support that evolutionary concepts contributed in a significant way to the most important medical issues, debates and new discipline in the period between 1880 and 1940.

Can Evolution Inform Insights into Normal and Adverse Pregnancy Outcomes and Ultimately Improve Maternal and Fetal Care?

Human survival, like all mammals’, is dependent upon successful pregnancy, the characteristics of which have been subjected to strong evolutionary pressures. This selection process for optimizing reproductive outcomes is unique in that two individuals are affected at the same time, the mother and fetus, and their respective interests may be either congruent or divergent. In this chapter, we provide an overview for considering evolutionary influences on pregnancy, general physiology of human pregnancy, and interactions of the mother and fetus that can either shape a healthy pregnancy or result in complications of pregnancy. Moreover, in considering research into mechanisms of pregnancy maintenance and parturition, we discuss the challenges and opportunities of differing reproductive strategies between species, altering selection in distinct ways, and making pregnancy in women unique amongst mammals.

Evolutionary Medicine Viewed Through the Lens of Pregnancy and the Obesity Epidemic

The rapid rise of the global obesity epidemic is one of the most significant microevolutions of the past century. Identification, evaluation and weight-altering interventions are sustainable only with an understanding that evolution occurs both at a macro level over centuries as well as on a micro level across a decade. Among the genes related to metabolism, on a global level, variation at the DNA coding level is to be expected. The unique distribution of these variants is shaped through hundreds of years of macroevolution to mature a population for survival of the fittest based on reproductive success. Over shorter time periods, these varied gene pools are further influenced by proximate response mechanisms within microevolution and co-inheritance. Microevolution prompts individuals’ responses to internal and external environmental pressures by changing gene activation and silencing.

The Functions of MicroRNA in Female Reproduction

MicroRNA (miRNA) are small RNA molecules of about 20–25 nucleotides in length which act to regulate gene expression post-transcription primarily by blocking the translation of messenger ribonucleic acid (mRNA). miRNA play important roles in the pathology of cancer, and also during normal pregnancy and lactation. The study of miRNAs related to cancer screening and treatment is perhaps the most developed of the clinical applications regarding miRNA, particularly for breast cancer. Evidence miRNAs affect pregnancy is strong, but the specifics remain poorly understood as the relationship between mother and neonate is complex. Within this relationship, miRNA in milk remain the most unknown, but it is hypothesized that milk miRNA play a role in regulation of both the mammary gland and in the neonate. This chapter describes ways biomedical researchers would gain from viewing miRNAs from an evolutionary perspective, specifically for research involving potential therapeutic interventions for women.