Chapter 3 Outline

Introduction

• Sleeping is one of the most important aspects of human life. We spend about a third of our lives doing it, and our daily well-being is shaped by how much of it we get, and sleep deprivation can lead to more serious maladies like memory loss, depression, chronic illness, and even death.
• Sleep also has complex cultural and behavioral dimensions. How, when, where, and with whom people sleep are patterned by collective social expectations, moralities, and available paraphernalia such as bedding, head rests, and sleep practices are a key site of enculturation in every society.
• From a holistic anthropological perspective, sleep is a complex phenomenon that intertwines human biology with the processes of culture, something anthropologists refer to as biocultural: a phenomenon that intertwines dynamics of human biology with processes of culture.
• Among hominins, sleep evolved under particular environmental and social conditions and sleep patterns were especially affected by bipedalism, which generated two conflicting evolutionary trends, one of structural refinements that saw the pelvis and birth canal get smaller to support bipedalism, and the other of increasing brain size to accommodate greater learning and social complexity.
• The resulting adaptive compromise was the birth of neurologically immature infants for whom the majority of brain growth occurs outside the womb which in turn created the need for increased and sustained parental contact with infants, a “dynamic, co-evolving interdependent system” between infant needs and parental response, which includes parents and infants sleeping together in close contact. Co-sleeping, along with breastfeeding, seem to have evolved as critical elements of human infant development, and both are involved in our reproductive success as hominins.
• While the majority of human societies continue close-contact sleeping with infants, in post-industrial Western countries, the prevailing belief is that babies should sleep alone. From an evolutionary perspective, this belief and the behaviors that stem from them put mothers and babies at odds with their bodies.
• At the heart of these issues is a larger question: How should we make sense of the biological and cultural factors that together shape our evolutionary trajectories? Embedded in this broader question are the following problems:
• Life changes. But what does it mean to say it evolves?
• What are the actual mechanisms through which evolution occurs?
• How do biocultural patterns affect evolution?
• Are modern humans evolving and where might we be headed?

Life Changes. But what does it mean to say it evolves?

• Living thigs change over time because of how they interact with environments and other life forms. But when is this change evolution and not simply change?
• Evolution is both a body of factual evidence—observable and verifiable truth—and a theory—a set of well-supported, testable hypotheses that explain how such changes occur.
• All societies give some form of classification to their worlds, explaining how things came to be and why there are similarities and differences between groups of people, animals, plants, and landscapes. Underlying these concerns is a key question: how can we explain the origins and diversity of life?
• Until recently, the dominant explanation in Western culture about the origins and diversity of life on earth combined Classical Greek and Roman philosophy and Judeo- Christian-Islamic theology. Another key concept was essentialism, which holds that organisms each have an ideal form, and that actually living versions of any organism are minor deviations from the ideal type.
• This enduring explanation for the diversity of life on earth holds that everything is ranked in a specific order, things do not change too much from their essential form, and it had all been done flawlessly by God so there is no reason to question it.
• During the sixteenth and seventeenth centuries a new emphasis on the careful observation of nature, sensory evidence, measurement, hypothesis building, mathematical proof, and experimentation contributed to radical new ways of thinking about these old questions.
• By the mid-1800s the table was set for a new and refined scientific theory to account for the diversity and origins of life on earth. Two naturalists, Charles Darwin and Alfred Russel Wallace, drew on elements of this intellectual history to make this new theory. Based on observations made during his travels of different plant and animal forms in different environments, Darwin saw these varieties as the result of interaction between organisms and their environment. Darwin argued that variations do not arise from a desire to change but are found in the pre-existing traits of individuals within a population.
• By 1844, Darwin had detailed his new theory, which he called “descent with modification via natural selection.” He did not use the term “evolution” because it might imply progress, improvement, and the possibility of an ultimate and perfect creation, all of which he rejected.
• One of Darwin and Wallace’s key interventions was the idea that change over time is intimately tied to variation in the present.
• Variations between physical traits that interest us from an evolutionary point of view are at the population level, as opposed to the individual level, and come about because of particular environmental challenges.
• Variations in physical traits are closely related to a life form’s survival. What also interests us from an evolutionary perspective are changes that come about through adaptation: the development of a trait that plays a functional role in the ability of a life form to survive and reproduce.
• For Darwin, that mechanism of adaptation was natural selection, which is not a force or a guided process, but a process of selection among traits that provide fitness in a particular environment. This means that evolution is non-directional: not progressive, linear, or necessarily leading toward improvement. Environmental changes can make a physical trait work against the population’s survival and not all changes are adaptive. What counts is the extent to which any changes enable a population to survive under very specific environmental conditions.
• Another key principle is that those traits that enable successful adaptations are inherited, that is, passed on across generations. Mendel’s earlier work connected traits of the offspring to specific parents, and thus characteristics of the offspring could be controlled by selective breeding. Mendelian inheritance provides a general understanding of the inheritance of physical traits, including the idea that each parent passes separate genetic material to their offspring and that dominant traits will mask recessive traits.
• Evolution also directs our attention to relational change. Changes always happen in relationship with other factors, primarily environmental conditions and what other life forms are up to, but also the specific biological and genetic factors unique to a population’s common ancestry. Understanding those relationships of common ancestry is thus critical to understanding the evolution of any life form.
• To establish common ancestry, it is necessary to have some way of naming populations. Development of the taxonomic system by Linnaeus that we use to organize and name organisms, called biological nomenclature, allows us to group together organisms with similar form into a genus (plural, genera) and those with more specific features into a species. Using the methods established by Linneaus, scientists are able to produce a taxonomy of all living forms on earth.
• Morphological similarities alone do not provide useful information about evolutionary processes because they do not capture the dimension of time, or the relationship between descendants and their ancestors. To describe those relationships, scientists create a phylogeny, a chart that looks somewhat like a family tree and traces the evolutionary history of a species or group, focusing specifically on points when an evolutionary event or change happens, such as the creation of a new species.
• Phylogenies are constructed using morphological, molecular, and fossil data. In creating phylogenies scientists look for three features:
• Shared characteristics, which are traits or structures that are shared by all or most species in a group because they are inherited from a common ancestral species.
• Derived characteristics, which are unique to a species, and evolved after two or more species who have shared a common ancestor diverged
• Shared derived characteristics, which are traits that evolved after all the species being compared shared a common ancestor, but prior to some more recent speciation events.
• Understanding distinctions between traits that are shared, derived, or shared derived helps us understand the evolutionary relationships between species.
• Evolution helps anthropologists understand our origins as a species, identify the evolutionary changes that make our species distinctive, and specify traits we share with other creatures with whom we have common ancestry. It also helps us make sense of biological and cultural variations between human populations.
• See “Classic Contributions: Clyde Kluckhohn and the Role of Evolution in Anthropology”
• Anthropology brings some very important things to evolution. It challenges the biological reductionism of much evolutionary theory, offering the holistic (“embracive”) perspective that Kluckhohn called for. Anthropology also brings culture into play, which also plays a critical role in human evolutionary history. Through culture, humans actively construct the worlds we live in. The selective processes emphasized in Darwin’s approach are not the sole—or necessarily even most important—means through which human populations evolve.

What Are the Actual Mechanisms Through Which Evolution Occurs?

• Since Darwin and Wallace’s time, we have learned a great deal about the relationship between evolution and genetic processes. Non-genetic processes are involved in evolution too, but we begin with an explanation of key genetic mechanisms.
• Darwin’s ideas were adopted in scientific fields during the late nineteenth century, including anthropology, because they offered a coherent theoretical framework with explanatory power, one that was open to empirical testing.
• By the 1930s and 1940s, new scientific fields like molecular biology and population genetics had shown there was a close relationship between genetics and evolution. The expanded description of evolution put forward by these scientists has been called the modern synthesis: the view of evolution that accepts the existence of four genetically- based processes of evolution: mutation, natural selection, gene flow, and genetic drift.
• A key feature of the modern synthesis is that evolution can only be measured across generations and within a population: a cluster of individuals of the same species who share a common geographical area and find their mates more often in their own cluster than in others.
• Individuals do not evolve in their lifetime, evolutionary change is only observable across generations, and this change is driven at the genetic level.
• The building block of our bodies, the basic unit of information for living things, and the primary means by which individuals pass on biological information to their children is the gene: a segment of DNA that contains the code for a protein.
• Genes, found in the nucleus of every cell, are the main unit of construction in our bodies. Variation in genes is at the heart of biological variation in organisms and acts as the basic source for biological change. Genes are segments of the filaments of Deoxyribonucleic Acid (DNA): spiral-shaped molecule strands that contains the biological information for the cell.
• DNA is inherited from our parents, and with it the genes that make up the DNA. A significant part of what DNA does is related to its physical and chemical structure.
• DNA has two main functions.
• Replication: the process by which DNA makes copies of itself.
• Protein synthesis: how DNA assists in the creation of the molecules that make up organisms (proteins).
• DNA copies—accomplished by replication—are necessary for two of the primary functions of cells:
• Mitosis: the process of cell division and replication.
• Meiosis: the process of gamete production.

• The organic structures of our bodies are made up of proteins, which are strings of amino acids, thus the function of protein synthesis.
• Parents pass on to their offspring DNA segments that provide the information for constructing proteins.
• A gene can be further defined as a segment of DNA that contains the sequence, or message, for a protein. All humans have the same genes, but for most genes, a number of different nucleotide sequences make up the protein message, each producing slight variants on the same final product, which are the observable physical traits. These are called alleles: the variants in the DNA sequences for a given gene.
• Comparing the DNA sequences of individuals, groups, or species can help us understand molecular patterns. This approach provides a method independent of morphological comparison for testing hypotheses about the taxonomic status and evolutionary histories of different species—in other words, whether creatures are connected through common ancestry.
• The modern synthesis accepts that there are four major processes that contribute to biological change in groups of organisms over time. These processes are involved in the creation, movement and shaping of genetic material, as well as the shape and function of living things. At the core of these processes is genetic variation, which arises through four evolutionary processes— mutation, natural selection, gene flow, and genetic drift.
• Variation initially arises with mutation: change at the level of the DNA (deoxyribonucleic acid).
• Our cells normally repair these changes, which usually have neutral or no effects anyway. An organism with negative mutations may not survive. Sometimes, however, changes are not repaired, creating variation. If there were no mutations among organisms in a population, each generation could only have the exact same genetic structure as its parent generation.
• Getting enough food, avoiding predators, and finding a mate for reproduction are difficult, and some individuals do better than others at these things. Biologists sometimes speak of the “survival of the fittest,” which really means competition for reproductive success—an organism’s number of surviving offspring.
• The greater the number of offspring that reach maturity and have offspring themselves, the better their reproductive success. If some individuals are better able to produce offspring than others, because of factors related to specific heritable traits, then over time the more successful (or “fit”) genetic variants will become more common in the population. This mechanism of change is called natural selection: the process through which certain heritable traits become more or less common in a population related to the reproductive success of organisms interacting with their environments.

• According to natural selection, over many generations the interactions between organisms and their environment result in gradual genetic shifts within a population. We can understand these shifts as changes in phenotype: the observable and measurable physical traits of an organism.
• Phenotype, not DNA, interacts directly with the environment. The physical traits of an organism must successfully pass through the environmental filter by reproducing successfully so it can leave more copies of its genotype: an organism’s genetic component.

• Gene flow is the movement of genetic material (DNA) within and between populations. Choosing a sexual partner affects the pattern and process of moving genetic variation around in two ways, through migratory movement and who individuals choose as their mates. Distant populations tend to experience less gene flow, nearby groups usually experience more. Gene flow can also occur through non-random mating.
• Other factors that can impact changes in the genetic component of a population include genetic drift: a change in genetic variation across generations due to random factors.
• Small populations offer opportunities to see genetic drift in action, because random events are more likely to have a genetic impact. The island population of Tristan de Cunha is a good example. Inbreeding on the island, as well as little gene flow, resulted in the high frequency of the alleles for the disease. This situation is known as the founder effect: a form of genetic drift that is the result of a dramatic reduction in population numbers so that descendent populations are descended from a small number of “founders.”

• While the modern synthesis revolutionized evolutionary theory, today many scientists, including anthropologists, argue that there are many non-genetic processes involved in evolution. This approach is called the extended evolutionary synthesis.
• Organisms are not simply like robots programmed by their genes, but also constructed during the developmental process of life itself. They might not “fit” into natural environments, but can shape those environments or co-evolve along with them.
• One non-genetic mechanism of evolution is seen in developmental bias: the idea that not all variations are random, but a function of the developmental processes organisms undergo during their lives that tend to generate certain forms more readily than others.
• Developmental processes can also explain how organisms adapt to their environments and become multiple species. Adaptation may happen over varying periods of time, sometimes within the life of an organism. This is referred to as plasticity: a particular form of developmental bias in which an organism responds to its environment by changing during its lifetime.
• Organisms are still influenced by environmental dynamics, but their ability to control certain environmental factors plays a role in their success. For example, termites build mounds in systematic and repeatable ways, reflecting previous selective processes, but the mounds they actually build in turn shape future selective processes. This is referred to niche construction: when organisms play an active role in their evolution by reshaping the environment to suit their own needs.
• As a species, humans are master niche constructors as we modify our environments through agriculture, technology, and other means in ways that have shaped our own evolution.
• The interplay between evolution and parenting is another type of non-genetic force in evolution that we call extra-genetic inheritance: the socially-transmitted and epigenetic factors that can aid in the adaptive success of organisms.

How Do Biocultural Patterns Affect Evolution?

• Building on the modern synthesis and the extended evolutionary synthesis, the approach presented here is known as a constructivist approach, which emphasizes that a core dynamic of human biology and culture is processes of construction: the construction of meanings, social relationships, ecological niches, and developing bodies.
• Jablonka and Lamb point out that explanations of human evolution have traditionally focused on only one system of inheritance—the genetic system—which relies on explanations at the level of genes. But human evolution also works in the epigenetic, behavioral, and symbolic inheritance systems.
• One such system is the epigenetic system of inheritance: the biological aspects of bodies that work in combination with the genes and their protein products, such as the machinery of the cells, the chemical interactions between cells, and reactions between types of tissue and organs in the body.
• The epigenetic system helps the information in the genes actually get expressed, and therefore it impacts genes as well as the whole body by altering an individual’s physical traits. Offspring may inherit those altered traits due to the past experiences of their parents.
• Another such system is the behavioral system of inheritance: the types of patterned behaviors that parents and adults pass on to young members of their group by way of learning and imitation.
• In humans there is also a symbolic system of inheritance: the linguistic system through which humans store and communicate their knowledge and conventional understandings using symbols.
• A critical aspect of our biocultural existence involves changing and constructing the world around us. A niche is the relationship between an organism and its ecology, which affects how that organism makes a living within a particular environment and leads to the construction of niches. The scale of niche construction and niche destruction can occur at the narrow local level or on a global scale and can change the kinds of natural selection pressures placed on the organisms involved. Many different types of organisms engage in niche construction.
• Much of what we take as “natural” in a landscape is actually an artifact of human niche construction and its effects. That human influence over ecosystems is the defining dynamic of our world today leads a number of scholars to adopt the term Anthropocene: the geological epoch defined by substantial human influence over ecosystems.
• Humans reorganization of ecosystems creates conditions for a co-evolutionary process in which humans, plants, animals, and microorganisms can mutually shape each other’s evolutionary prospects. Thus, niche construction creates a kind of “ecological system of inheritance”.
• Another foundation of the biocultural perspective is the shift in thinking about evolution that came with the introduction of Developmental Systems Theory (DST.
• DST focuses on the development of biological and behavioral systems over time rather than on genes as the core of evolutionary processes and rejects the idea that there is a gene “for” anything. Evolutionary processes are fundamentally open-ended and complex because they involve the ongoing assembly of new biological structures interacting with non-biological structures.
• In this sense development comes from the growth and interaction of several distinct systems: genes and cells, muscles and bone, and the brain and nervous system. All develop over the lifetime of the individual. Thus, evolution is not a matter of the environment shaping fundamentally passive organisms or populations, as suggested by natural selection theory, but consists of many other developmental systems simultaneously changing over time.
• Genetic mechanisms are not the sole force in human evolution. The constructivist approach here acknowledges that biocultural dynamics are open-ended and involve interactions between diverse forces and agents, which help us understand how humans are currently evolving.

Are Modern Humans Evolving, and Where Might We Be Headed?

• A common notion circulates around evolution suggesting that “it happened in the past.” This is not the case, because evolution continues, unabated, until a species becomes extinct. Humans are continuing to evolve. Human evolutionary patterns are complex and there is often a fuzzy line between biological and cultural influences.
• Disease has an impact on evolution. Consider the common cold which is widespread in our species and for which we have no cure. The SARS virus, a variant of the common cold which first appeared to us in 2002, may have been passed to humans through close contact, butchering, or undercooked meats. Human cultural behavior combined here with an evolving virus to threaten members of our species, creating a new evolutionary pressure on humans.
• For every major disease outbreak (for example, Bubonic plague, smallpox, flu, or cholera) in which members of a population die, a set of genetic complexes disappears from that population. Evolution is taking place here: when the epidemic subsides, the surviving population is genetically different from before because there has been a change in allele frequencies.
• Note, however, that biocultural practices strongly shape the experience and effects of disease. Consider the human immunodeficiency virus, or HIV, which causes AIDS. While there is no cure, medicines make it possible for some afflicted individuals to stay alive. The selective impacts of HIV are decreased if those individuals reproduce. Since the effects of any disease and access to those biocultural medical practices are uneven, AIDS remains a fatal disease in many less economically developed nations, and is not the manageable chronic condition it is in North America and Europe.
• What is important here is that the evolutionary pressures of diseases affect different populations differently because of the differential access people have to healthcare, a product of broader socioeconomic and political relationships and processes.
• Cultural practices, such as diet, body modifications, and patterns of daily activity, have the capacity to alter human morphology, which refers to the shape and form of the human body.
• Although all humans need certain basic nutrients and calories to survive, grow, and reproduce, different populations get those nutrients in varying quantities. Variable access to nutrition may help explain differences in bodily shape and form between and within human populations. While an individual’s height and weight range are inherited, dietary practices, interacting with both physiology and morphology, strongly shape the body’s actual form. Relative caloric, dietary fat, and carbohydrate contents of any given diet does affect body shape and physiology.
• See “Anthropologist as Problem Solver: Clarifying the Biocultural and Evolutionary Dimensions of Obesity”
• In addition to diet, humans have long adorned themselves with things that change their appearance. People usually modify their bodily appearance because of cultural beliefs about attractiveness. While these can enhance an individual’s reproductive fitness, unless the practice actually affects fitness, it may not have any long- term evolutionary impact.
• Daily activity patterns can have evolutionary consequences, since they can directly affect reproductive physiology. The consequences of migration, modern transportation or sitting for long periods, can greatly impact individual physiology, and can be seen in a range of conditions such as chronic high blood pressure and heart disease to reduced fertility.
• Gene flow is our most easily observable evolutionary process today. High rates of transnational migration, which bring diverse populations into contact, produce important changes in alleles. Cultural changes contribute to migration and the movement of alleles.
• The overall effects of such migrations for modern humans include reduced differences in allele frequencies between populations and increased overall genetic variation within populations. Long-term impacts of cultural practices of diet, body modification, and daily activity level are less predictable.

Looking to the Future

• Over the past 50,000-40,000 years, most evolutionary changes have occurred through gene flow, adaptive immune responses to new diseases, and cultural changes in behavior. However, evolutionary change is a constant of nature, and looking ahead, three biocultural issues could affect our evolutionary future as a species: population growth, genetic manipulation, and adaptive behaviors.
• The global human population has grown dramatically in recent decades. Ten thousand years ago, between 5 and 20 million humans inhabited the planet. Today, it is 7 billion. Unequal distributions of technology, wealth, and access—not genetic causes—will shape how human populations adapt to the challenges of a rapidly growing global population.
• We do know that as a population grows, genetic diversity tends to increase. This has adaptive potential for the species, but only as long as individuals reach reproductive age and have children to pass on that genetic material.
• Humans have added yet another force of evolution: direct genetic alteration. We can alter allele frequencies, and even create new alleles for transgenic (across species) insertion into organisms.
• From an evolutionary perspective, hundreds of generations will probably have to pass before we can tell if genetic manipulations have long-term effects on our species. One effect of the hype around genetic manipulation is the increasing extent of geneticization: the use of genetics to explain health and social problems over other possible causes.
• When a behavior emerges that gives individuals within a population some kind of reproductive advantage, it is considered adaptive. We do not know how much how much of current behavioral patterns emerged during our evolutionary past and how much expresses our broad behavioral potential that is made possible by specific current environments.
• When a behavior emerges that gives individuals within a population some kind of reproductive advantage, it is considered adaptive. We do not know how much how much of current behavioral patterns emerged during our evolutionary past and how much expresses our broad behavioral potential that is made possible by specific current environments.
• Some researchers argue that many human behavioral patterns were adaptive responses of humans who lived as hunter-gatherers many thousands of years ago. Others argue that most modern human behavior emerges through the life experiences of individuals and the political, economic, and historical contexts in which they live and are not a reflection of specific past adaptations.
• It is hard to predict our behavioral futures because our behaviors are not purely genetically determined and inflexible. It is simply too hard to separate biology from culture, which is why anthropology’s holistic and integrative approach is so important.

Conclusion

• Patterns of evolutionary change are complex. Understanding them through a biocultural lens may be new, but it builds on foundations of evolutionary theory.
• The biocultural lens allows us to focus on both genetic and non-genetic evolutionary processes, emphasizing that biocultural dynamics are open-ended, emergent, and shaped by many different kinds of interactions.
• Humans are still evolving and many forces, such as disease, diet, and migration, are affecting our morphologies. It is unclear as to what the evolutionary impacts of these forces may be, and it is too hard to predict because of the complex interplay between culture, behavior, and biology.