Human biology

Human biology entails the study of human beings as physical, or biological, organisms. This is a highly complex field of study that encompasses many different fields of science and academic disciplines, including biology (the study of life in general), physical anthropology (the branch of anthropology that studies the biological dimensions of the human experience, such as our evolutionary past), primatology (the study of primates and their biological and evolutionary relationships to one another), genetics (the study of DNA), osteology (the analysis of bones and skeletal structures), epidemiology (the study of the origins and evolution of various diseases, along with the social and cultural dimensions of diseases), neurology (analysis of the nervous system), odontology (the study of teeth), paleontology (the study of ancient hominids and their impact on modern humans), and biochemistry (the study of chemical reactions within the body), among many others. Given the inherent intricacies of this subject, human biology is studied at several different levels, from that of the species as a whole (which focuses on the universal aspects of human biology that differentiate us from other forms of life), to that of the level of a population or group, to that of the individual (which focuses on the distinct and unique physical traits, features, genes, or biological makeup of a particular person).

The study of human biology is not new, as people throughout history have sought to better understand humans’ physical and natural characteristics since prehistoric times for nutritional, medical, scientific, and other purposes. The study of human biology serves several important functions. In addition to improving medical research and treatments, knowledge of human biology also increases the understanding of human evolution, as well as how humans’ unique biological features have given human beings the capacity for culture.

Brief History

All human beings today are members of the species Homo sapiens, the scientific nomenclature that translates from Latin as "wise man" or "man the thinker." However, to be more exact, all present-day humans belong to the even more specific subspecies Homo sapiens sapiens. The majority of physical anthropologists believe that Homo sapiens sapiens—in other words, modern humans—first evolved from earlier hominids in East Africa’s Rift Valley, located in present-day Ethiopia and Kenya, approximately 190,000 to 200,000 years ago and subsequently migrated throughout the rest of the African continent and into other regions of the world over time.

Modern humans likely coexisted with other Homo species, such as Neanderthals (Homo neanderthalensis), for several thousands of years, and some genetic studies suggest that these groups may have interbred with one other. This hybridization would have influenced human evolution, and therefore human biology. In any case, humans evolved into a highly adaptable species characterized by bipedalism (walking upright on two legs), a large brain, and other physical differences from other primates, including less body hair and less sexual dimorphism. Still, humans and chimpanzees—humans’ closest relatives, genetically speaking—share DNA that is more than 98 percent identical.

Genetic variation naturally leads to differences in phenotype, or observable appearance, within a species. As Homo sapiens spread out across the globe, different populations adapted to different climates and other conditions, leading to the development of certain characteristics that became associated with certain geographic regions, cultures, or other groupings of people over long periods of time. As people gained the ability to travel long distances, encountering other people from other lands with sometimes apparently drastic physical differences, the concept of biological races within the human species began to emerge. Such beliefs were dominant in the eighteenth century as modern biology developed and became deeply entwined with early theories of human biology. However, physical and genetic evidence indicates that the common racial categories that persist in society—and which often serve as a basis of identity for many people—are not, in fact, biological divisions of humankind but rather social labels that have been arbitrarily defined.

The belief in biological human races gained popularity in the context of European colonialism, in which explorers of Western European heritage encountered peoples living in other regions of the world—the Americas, Africa, Asia, and Oceania—who looked very different from themselves and had vastly distinct cultural, linguistic, and religious practices. Western European thinkers were simultaneously developing what would become modern science, so their racial views held sway as biology emerged as a distinct field of study. Before human genetics were understood, racial phenotypes were often misinterpreted and manipulated to serve social and political goals, blurring science with speculation and racism. No scientific or scholarly consensus has ever existed as to how many supposed human races there are, reflecting the inherently arbitrary nature of dividing humans into distinct racial categories. Some attempted to classify biological human races by continent (Europeans, Africans, Asians, American Indians, etc.), while others argued that each continent consisted of several or many different biological races (so that, in other words, southern or eastern Europeans would be considered distinct races from northern and western Europeans).

However, the discovery of DNA and the establishment of genetics as a key scientific field in the 1950s and 1960s enabled researchers in human biology to test longstanding assumptions about race and human biology. While modern genetics suggests that some groups commonly classified as races can potentially be identified by some genetic markers, such as predisposition to certain diseases, the great complexity of genes and phenotypes—and the subjective nature of race—means that the vast majority of scientists reject old models of racial biology. Many physical traits among humans, including skin color, eye color, hair color, and hair texture, are clinal in nature, meaning that they occur not just in a few distinct, sharp types but rather exist as a spectrum, gradient, or continuum that manifest in many different degrees. For example, human skin color—the trait most often used as the basis for racial categories—is a clinal trait that ranges from very light to very dark, with every possible shade or tone between. Furthermore, other traits that were once considered evidence of distinct biological races (such as the epicanthic eye fold, associated with East Asians, or even genetic markers such as the sickle-cell gene, associated with those of African descent) have been shown to also exist outside of the groups once associated with such traits.

Instead of race, biologists and physical anthropologists today analyze human biological variation through the framework of population genetics. Within biology, a population is a cluster of individuals who share a common geographic territory and most frequently choose their mates from within this cluster/territory than from outside of it. A biological population is not the same thing as a biological race; racial categories as we commonly know them are based on certain arbitrarily selected physical traits (such as skin color, eye shape, and hair texture) while ignoring other biological traits (such as blood type, eye color, or fingerprint shape). Both white and black people in the United States, for example, each consist of a variety of populations, and these different populations do not share identical genetic features because they have different geographic ancestries and histories.

The human genome (a genome is the total volume of DNA sequences within a species) was fully sequenced in 2003, the same year in which the fifty-year anniversary of the discovery of the model of DNA was celebrated. Within humans, the genome is approximately 3 billion base pairs long, but only a small portion of total human DNA appears to code for particular traits. A 2014 article published in the peer-reviewed scientific journal Human Molecular Genetics claimed that humans have only approximately 19,000 genes, far fewer than in predictions made before the sequencing of the human genome that estimated humans would have 100,000 or more genes.

Genetics remains critical to the advancement of biology in general and human biology in particular. However, it is not the only subfield that continues to expand knowledge of the human organism. Biologists are among the many scientists who frequently debate the classic "nature versus nurture" question, in which genetics is often understood to represent nature and biological imperatives while the various environmental and cultural influences on organisms represent nurture. The human environment, in particular, is profoundly shaped by social interaction, and the study of human biology benefits from ongoing research in fields such as demography, early childhood development, behavioral science, epidemiology, and nutritional studies. Groundbreaking studies in epigenetics further suggests that human biology is truly a product of numerous complex factors at both the individual and the species levels.

Overview

Although significant physical and genetic variations can be found among modern humans, certain universal features also exist. For example, a normal human cell has forty-six chromosomes (large, tightly coiled bundles of DNA located within the nucleus of cells), which occur in twenty-three pairs. Certain exceptions to this standard do exist, however, as a result of genetic mutations such as the insertion or deletion of an entire chromosome. Such variations cause a range of conditions and disorders, often with both physical and mental symptoms. Down syndrome, for example, results from an extra partial or full chromosome. Chromosomes also determine biological sex and the accompanying physiological differences; males have an X and a Y chromosome in the twenty-third pair, while females have two X chromosomes. The subfield of human genetics is among the most cutting-edge sciences and reveals how hugely influential genes are in human biology.

Above the level of genetics, the human body as a biological system is characterized by a number of subsystems that each carry out specific functions, such as the nervous system, respiratory system, and cardiovascular system. It can also be described based on different bodily regions, such as the head, chest, arms, and legs. The study of the body’s structure is known as anatomy, while the study of its functions is known as physiology. While the anatomical and physiological aspects of human biology are most commonly studied by health professionals, who must be familiar with the human body regardless of their subfield, they are also important to many research scientists, anthropologists, and others.

The skeleton, made up of bones, provides the basic structure of the human body. Bones also provide a measure of protection for many of the softer internal organs. Adult humans, both male and female, have 206 bones in their bodies, most in the hands and feet. Several of these are formed by the fusion of smaller bones that are initially separate at birth. The largest bone in a person’s body is the femur, more commonly known as the thighbone. Tooth enamel constitutes the hardest part of the human body, and adult humans normally have thirty-two teeth, aside from wisdom teeth. Further bodily structure is provided by the muscles, which allow movement of the body, as well as fatty tissue. While differences in individual body shape and appearance are influenced by the amount of muscles and fat (which in turn depend on genetic factors as well as activities levels and diet), the basic elements are the same in all humans.

The nervous system, perhaps the most complex biological system, involves the brain interpreting sensory signals via nerves and responding appropriately by triggering muscular movement or by other means. The respiratory system is responsible for bringing oxygen—a critical component of the cellular process—into the body, with the lungs as the key organ involved. The circulatory system, or cardiovascular system, provides nutrients and oxygen to the cells by using the heart to pump blood through veins and arteries. It also removes the waste products of cells. The digestive system brings in nutrients through food, which it breaks down, and removes waste from the body. Other systems of the human body include the endocrine system, the exocrine system (integumentary system), the lymphatic system, the renal system, and the reproductive system.

Bibliography

Chiras, Daniel D. Human Biology. Jones & Bartlett Learning, 2015.

Garcia, Richard. "The Misuse of Race in Medical Diagnosis." Chronicle of Higher Education, vol. 49, no. 35, 2003, pp. B15.

Harcourt, A. H. Humankind: How Biology and Geography Shape Human Diversity. Pegasus, 2015.

Lieberman, Daniel. The Story of the Human Body: Evolution, Health, and Disease. Pantheon, 2013.

Parrington, John. The Deeper Genome: Why There is More to the Human Genome than Meets the Eye. Oxford UP, 2015.

Relethford, John. Reflections of Our Past: How Human History is Revealed in Our Genes. Westview, 2004.

Ryan, Frank. The Mysterious World of the Human Genome. Prometheus, 2016.

"What Is Human Biology?" Michigan Tech, www.mtu.edu/biological/undergraduate/human-biology/what/. Accessed 10 Feb. 2025.