Haematopoietic System

The haematopoietic system provides numerous essential functions for animals, including transport of gases and nutrients, wound repair, and host defence. Given the fundamental importance of the blood system, these roles are conserved across animals, with specific features shaped by the unique needs and adaptations of different organisms. While even the simplest organisms have haematopoietic systems, increasing size and complexity of organisms has necessitated the evolution of more efficient clotting and oxygen transport systems, more complex circulatory systems, and more diverse blood cell lineages for immune defence. Evolution has sculpted haematopoietic systems for different animals by modification of previously existing programmes and developmental systems, with striking examples of conservation and convergent evolution in the blood systems of distantly related organisms suggesting common adaptive solutions to a range of selective pressures. Notably, our own haematopoietic system recapitulates many features found in ancestral organisms. This chapter discusses how blood and vascular systems have evolved together and share common endothelial heritage, as well as how different blood lineages are produced and how they have evolved to meet new challenges from pathogens. Moreover, it examines how pathogenic threats to blood cells have influenced modern population genetics for humans and in turn impact our susceptibility to various disorders of the blood system. Finally, the chapter suggests how evolved life histories to maximise reproductive success have influenced ageing and disease patterns, such as for blood cancers.

Musculoskeletal System

This chapter on the musculoskeletal system aims to give an overview of the evolutionary implications for health and diseases of this body system. Using specific examples, the chapter shows how musculoskeletal diseases develop from an evolutionary point of view, with a specific emphasis on mismatches between the evolved human body and the modern environment, as well as on consequences of human bipedal gait. The chapter discusses the evolutionary aetiology of common musculoskeletal disorders as a consequence of mismatch to the modern world, such as carpal tunnel syndrome, flat feet, osteoporosis, and impacted third molars. As a consequence of the passage to bipedalism, the evolutionary background of low back pain, and knee and hip arthritis is examined. The chapter concludes with a discussion of implications for treatment and prevention of musculoskeletal diseases, focusing on the life course approach to health. In fact, every life stage shows specific needs and asks for specific interventions in order to optimally maintain musculoskeletal health up to old age.

Growth and Development

An evolutionary and biocultural approach is taken to the study of human growth and development. The evolutionary perspective focuses on the unusual process of human postnatal growth and development, a process that takes two decades to complete and traverses the stages of infancy, childhood, juvenility, and adolescence. Human childhood and adolescence are highly unusual even compared to our closest living relatives, perhaps unique. The biocultural perspective of human development focuses on the constant interaction taking place during all phases of human development between genes and hormones within the body and the sociocultural environment that surrounds the body. While humans are often considered to be cooperative breeders, depending on social group helpers to successfully rear offspring, it may be more accurate to understand humans as practising biocultural reproduction as an adaptation to minimise risks to health.

Endocrinology

This chapter on endocrinology aims to shed light on the biology of hormones within the context of human life history evolution. An evolutionary perspective contributes to not only our understanding of human evolution, but also to the contemporary and emerging health challenges across the spectrum of ecologies and environments. Evolutionary endocrinology extends our understanding of human biology and health through the engagement of gene–environment interactions, social dynamics, human variation, and how hormones regulate life history traits such as growth, immune function, metabolism, and ageing. This chapter describes key aspects of endocrinology that are specific to men and women, while also being mindful of the importance of human variation. For example, men and women exhibit reproductive states that deploy specific functions. In women, these are menstruation, gestation, and lactation. These processes are governed largely by the hypothalamic–pituitary–ovarian axis and how it responds to environmental challenges such as nutritional demands, activity, and social stresses. Men also exhibit reproductive states, although they are mostly in the form of investment in sexually dimorphic tissue and behavioural variation. These states are governed by hormones which allocate resources between tissues that are indicative of different forms of reproductive effort. These include sexually dimorphic muscle tissue and adiposity. Spermatogenesis is obviously key but has differential effects on fertility compared to gametogenesis in women. Additional aspects of human evolutionary endocrinology include stress homoeostasis and metabolism, which involve the hypothalamic–pituitary–adrenal axis as well as the thyroid and other metabolic hormones.

Digestive System

Digestive tracts vary considerably because animals have evolved different processes to convert foods to essential molecular building blocks. Differences in digestive strategies distinguish, for example, foregut and hindgut fermenters, and animals utilising different dominant food types, for example herbivores, carnivores, and folivores. Neither the modern human diet nor the size and proportions of the human gut resemble those of other primates. The human digestive system has evolved and diverged in response to introduction of new food types and food preparation techniques. For example, persistence of lactase activity into adulthood occurred in populations that maintained cattle to harvest milk. Humans have utilised non-thermal food preparation for over 2 million years and cooking for 300,000–400,000 years. For most extant humans, prepared food comprises over 70% of the diet. The modern human digestive system is suited to pre-prepared food because of its smaller volume, relative to other species, and because of differences in dentition and masticatory muscles that results in lower bite strength. Adaptations of human digestion in response to diet involved genetic selection over thousands of years. However, transmissible changes linked to diet occur in a single generation. These are best documented for epigenetic changes related to obesity, and are maladaptive in some cases. Diets for most humans have changed substantially in the last half century, too rapidly for evolutionary change in digestive physiology. The capacity to adapt to recent dramatic dietary changes has proven insufficient to avoid deleterious effects leading to obesity, diabetes, fatty liver disease, and metabolic syndrome.

Cardiovascular System

Cardiovascular (CV) disease is the leading killer of our species. Various evolutionary lenses can be applied to better understand human vulnerability to CV disorders. The evolutionary origins of a healthy human heart—its myocardial, electrophysiologic, valvular and vascular systems—offers a history of the selective pressures, trade-offs and adaptations leading to the normal mammalian CV systems. Beyond these evolutionary-developmental perspectives, the application of a framework based on Tinbergen’s four questions offers a novel evolutionary lens for understanding our species’ vulnerability to CV pathology. This is done by a consideration of comparative information about non-human animals who spontaneously develop the same CV diseases. This phylogenetic information can then be used to develop trade-off-based adaptive hypotheses to explain the nature and origins of vulnerability to a range of CV pathologies including atherosclerosis, heart failure, valvular heart disease and arrhythmias.

Immune System

As humans move from the natural environment in which we evolved into modern urban settings, there are striking increases in chronic inflammatory and psychiatric disorders. To understand and eventually take control of this phenomenon we have to understand how humans, and in particular our immune systems, evolved in partnership with microorganisms in the environment and in our own bodies. Humans are holobionts, composed of human cells containing the human genome passed on via the germline, but also a much larger number of microbial cells acquired from mother, family members, and the environment. This microbiota provides signals involved in the development of essentially all organ systems, including the brain, and provides data and signals that regulate metabolism and the immune system. The immune system evolved to perform the dual functions of managing this microbiota, while simultaneously protecting us from pathogens. By considering the evolution of the immune system and the ways in which lifestyle changes have altered our exposures to, and colonisation by microorganisms, we can identify the crucial factors leading to the modern urban pattern of disease.

Cellular Signalling Systems

Effective reception, delivery, and processing of information is fundamental to all life forms. Physical and chemical signals are perceived from both outside and inside an organism. The nature, duration, and intensity of signals are processed into information, mainly encoded as concentration differences of ions and molecules that ultimately lead to a reaction of the organism. Although the advent of the first and most primitive signalling system will remain unknown, it probably existed already in the first hours of life. Disturbances of well-orchestrated signalling systems are often the basis of diseases. Understanding the complexity of signalling networks is required for rational intervention in different disease stages. Understanding the evolutionary history of signalling systems can help us unveil the requirements for proper functioning of a given signalling network. This chapter provides an overview of how cellular communication evolved, works, and contributes to our understanding of human diseases in the light of evolution.

Respiratory System

The lung is the gas-exchange organ that provides oxygen and removes carbon dioxide from the blood. The environment in which animals live and their metabolic needs determine the evolved design of their gas exchange system. Gills are the primordial respiratory organs that evolved for water ‘breathing’, while other adaptive solutions evolved for bimodal breathing, that is, the ability to extract oxygen from both water and air. The transition to fully terrestrial life was accompanied by significant changes in dimensions of respiratory units (alveoli) which decreased in size, whereas the number of units and total lung volume increased, leading to more efficient gas exchange and oxygen supply. While the shape and make-up of lungs in humans suggest adaptations to long-distance running and possibly to the exposition of smoke caused by fire, the exposure of the human respiratory system to novel environments has brought about a diverse array of disease patterns, including lung cancer, autoimmune diseases, and infectious diseases.

Brain, Spinal Cord, and Sensory Systems

The central nervous system (CNS) comprising the brain and the spinal cord is the control system of bodily functions and processes incoming information from the external environment via diverse sensory systems. Incoming information from the body (interoception) and from the environment (exteroception) is integrated and utilised in complex patterns of action and re-action (allostasis) to maintain homoeostasis and ensure survival and reproduction. The brains of primates are larger than expected for their body weight, whereby the human brain is not exceptional in terms of the number of neurons. However, connectivity and cross-talk between different brain areas has increased during human evolution. The adult human brain consumes about 20% of total energy intake, which is needed to maintain complex excitatory and inhibitory mechanisms with the aid of glia cells and microglia. Abnormal amounts of stress during different stages of development may expose the CNS to an excess of toxic and inflammatory metabolic products, which may cause neuropsychiatric disease and disorders. Such stressors may include, among other factors, adverse events such as abuse or neglect during childhood, immunological mismatches between ancestral and current environments, and a plethora of social challenges related to ‘modern’ cultural peculiarities. Gene–environment interactions involved in CNS disease processes are far from being fully understood. Preventive measures to protect the CNS from premature functional deterioration may include safe-guarding child development, a reduction of toxic waste products, and mental and physical exercise.