Chapter 13 Human Adaptation to a Changing World. Chapter Preview How Have Humans Adapted Biologically to Naturally Occurring Environmental Stressors?

Chapter 13

Human Adaptation

to a Changing World

Chapter Preview

How Have Humans Adapted Biologically to Naturally Occurring Environmental Stressors?

What Is Evolutionary Medicine?

How Are Humans Adapting in the Face of Globalization?

How Have Humans Adapted Biologically to Naturally Occurring Environmental Stressors?

The Ethics of Human Biological Research

When examining seemingly biological phenomenon such as disease, cultural factors must be considered at every level—from how that phenomenon is represented in each social group to how biological research is conducted.

This study denied medical therapy to African American men in order to study supposed differences in the disease in this population.

Public outcry about the study led to regulations that protect human subjects in biomedical research.

The Ethics of Human Biological Research: The Tuskegee Syphilis Study

Types of Human AdaptationHumans have biological mechanisms for adapting:

Genetic adaptation Described by Darwin’s theory of natural

selection. Developmental adaptation

Permanent phenotypic variation from interaction between genes and the environment during development.

Physiological adaptation Short-term physiological change in response

to a specific environmental stimulus.

Human Growth Curve

Franz Boas defined the features of the human growth curve. The graph on the left depicts distance, or the amount of growth attained over time, while the graph on the right shows the velocity, or rate of growth over time.

Human Growth Curve

Boas found that immigrant children had different growth curves than their genetically similar parents.

This is an example of a secular trend = a physical difference among related people from distinct generations that allows anthropologists to make inferences about environmental effects on growth and development.

Acclimatization

Long-term physiological adjustments made in order to attain an equilibrium with a specific environmental stimulus.

• It takes between 2 weeks and 2 months for your body to adapt to living at higher altitude. Most of it happens without an individual even being aware of the changes.

• In children, lungs naturally grow larger to accommodate the need for increased oxygen. At very high altitudes, this results in a more "barrel chest" appearance.

• In adults, lungs may have difficulty in high altitudes with low oxygen and air pressure so, the body produces additional red blood cells to carry oxygen more efficiently

• You also require more water at higher altitudes.

High Altitude Acclimatization (above 5000 ft.)

High Altitude Acclimatization (above 5000 ft.)

High Altitude Acclimatization

Observing that Kenyan runners have won most of the major marathon competitions over the past several decades, coaches have emulated the Kenyan approach.

Adaptation to the hot, dry yet mountainous region leads to a long lean build and increased oxygen-carrying capacity.

Adaptation to Heat and Cold: Bergmann’s Rule

From biology, it states that warm-blooded animals from colder climates usually have larger body masses than the equivalent animals from warmer climates.

Adaptation to Heat and Cold: Allen’s Rule

Also from biology, it states that warm-blooded animals from colder climates usually have shorter limbs than the equivalent animals from warmer climates.

Human Biological Diversity: For Class Discussion

Why would the stocky body and short limbs characteristic of populations adapted to the cold of the Arctic or high altitude, as in this person from the Andean highlands of Peru (left)?

Why would a tall, thin body, as seen in the Maasai of Kenya (right), be well adapted to the heat?

The Hunting Response

In extreme cold, the limbs need enough heat to prevent frostbite, but giving up heat to the periphery takes it away from the body core.

Humans balance this through the hunting response: When exposed to cold blood vessels constrict. Initial alternations between the open (warm)

and shut (cold) and the temperature of the skin range dramatically.

Oscillations become smaller and more rapid, allowing a hunter to maintain manual dexterity required for tying knots or sewing.

Physiological Adaptation to Heat The human body’s primary physiological

mechanism for coping with extreme heat is sweating or perspiring.

Sweating is a process through which water released from sweat glands gives up body heat as the sweat evaporates.

Without replacing sweat through drinking water, exposure to heat can be fatal.

What Is Evolutionary Medicine?

Medical Anthropology

A specialization that brings theoretical and applied approaches from cultural and biological anthropology to the study of human health and disease.

A medical system is a patterned set of ideas and practices relating to illness.

Disease and Illness

A disease is a specific pathology; a physical or biological abnormality.

An illness refers to the meanings and elaborations given to a particular physical state.

The term endemic is used to describe a disease that is widespread in a population.

Visual Counterpoint: For Class Discussion

Shamans and biomedical doctors both rely upon manipulation of symbols to heal their patients. The physician’s white coat is a symbol of medical knowledge and authority that communicates to patients just as clearly as does the shaman’s drum.

Visual Counterpoint: For Class Discussion

Both shamans and medical doctors also make use of restricted knowledge to help their patients.

Can you think of other ways in which cultural values and customs interact with disease and medical systems?

Problems with Modernization

Building the Aswan Dam in Egypt was a vital part of modernization for that country.

Unfortunately, the dam increased the rates of schistosomiasis in the Nile River by creating a massive artificial lake upstream from the dam that provides the ideal environment for water snails.

Evolutionary Medicine

Evolutionary medicine uses the principles of evolutionary theory to contribute to human health.

Basic to this approach is framing health issues in terms of the relationship between biological change and cultural change.

Symptoms of Disease as Defense Mechanisms

Evolutionary medicine proposes that many of the symptoms – fever, vomiting, coughing, and diarrhea -- that biomedicine treats are themselves part of the body’s defense mechanism against infections.

Battling Disease: Culture vs. Evolution

North American medical anthropologist Emily Martin has shown that scientific depictions of infectious disease draw upon military imagery common to the culture of the United States.

An evolutionary perspective suggests that the quick life cycle of microorganisms makes this “battle” a losing proposition for humans.

Evolution and Infectious Disease Viruses, bacteria, fungi, and parasites all have very

short life cycles compared to humans.

When competing on an evolutionary level, they will continue to pose new threats to health, because any new genetic variants appearing through a random mutation will become incorporated in the population’s genome more quickly.

While antibiotics will kill many bacteria, increasingly resistant strains of bacteria are becoming more common.

Prions

A prion is a protein lacking any genetic material that behaves as an infectious particle.

Prions are a kind of protein that can cause the reorganization and destruction of other proteins and result in neurodegenerative disease as brain tissue and the nervous system are destroyed.

Mad Cow Disease and Prions The beef supply of several countries in Europe and

North America became tainted by prions introduced through the cultural practice of grinding up sheep carcasses and adding them to the commercial feed of beef cattle.

Through the wide distribution of tainted feed, prion disease spread from sheep to cows and then to humans who consumed tainted beef.

Today countries without confirmed mad cow disease ban the importation of beef from neighboring countries with documented prion disease.

Medical Pluralism

The presence of multiple medical systems, each with its own practices and beliefs in a society.

Most individuals can reconcile different medical systems.

Medical pluralism may become increasingly necessary in areas of public health.

How Are Humans Adapting in the Face of Globalization?

Globalization and Human Adaptation

The term globalization refers to the increasing interconnectedness of humans to one another and to the environment.

Understanding globalization is critical for understanding human adaptation and disease.

By examining the political ecology of disease, we can

reveal its social causes, bringing us closer to finding long-lasting cures.

Structural Violence

Physical and/or psychological harm (including repression, environmental destruction, poverty, hunger, illness, and premature death) caused by exploitative and unjust social, political, and economic systems.

A Health disparity is a difference in the health status between the wealthy elite and the poor in stratified societies.

Economic Disparity After a natural disaster such

as Hurricane Katrina, the ability to recover is determined by the relative wealth and resources available to the community.

In the hard-hit Lower 9th Ward of New Orleans, for example, a year after water levels rose to above the rooflines of houses, much of the neighborhood is still in disarray.

Human Population Growth

Since the industrial revolution, human population size has been doubling at an alarming rate. The earth’s natural resources will not be able to accommodate ever-increasing human population if the rates of consumption seen in Western industrialized nations, particularly the United States, persist.

Diet and Health

The definition of malnutrition includes under nutrition as well as excess consumption of unhealthy foods. Obesity is common among poor working-class people in industrialized countries. Starvation is more common in poor countries or in those that have been beset by years of political turmoil, as evident in this emaciated North Korean child.

Decline in Sperm Counts

A documented decline in human male sperm counts worldwide may be related to widespread exposure to hormone-disrupting chemicals.

Health Education

These Gambian children are spending their Saturday in the school library to make up skits and songs about health issues that they will take out into their local community.

They are a part of a peer health educator group, a tradition that stretches throughout The Gambia and beyond.