Topic 1

Darwinian Medicine

• Uses evolutionary theory and natural selection → why humans get diseases and why the human body is not perfectly designed.

• Recognizes that adaptations can involve trade-offs:

  • A trait that was beneficial in one environment may become harmful in another.

• Health and illness can be understood as an emergent property of interactions between humans and their physical environment.

Evolutionary Medicine

• Applies the principles of natural selection to understand health and disease.

• Developed particularly through the work of Randolph Nesse and George Williams.

• Explains why diseases exist rather than assuming every disease reflects a biological "design flaw.”

• Focuses on both the mechanisms of disease and the evolutionary reasons those mechanisms exist.

Natural Selection

• Organisms within a population have different levels of fitness.

• Fitness refers to the ability to survive and reproduce.

• Individuals with traits that improve reproductive success contribute more to the gene pool.

• Over generations, differential reproduction can change populations.

Requirements for Natural Selection

1. Variation must exist within a population.

2. Variation must be heritable across generations.

3. Different variations must produce differences in survival or reproductive success.

Fitness

• Refers primarily to an organism's ability to survive long enough to reproduce.

• Natural selection maximizes reproductive success, not necessarily health or longevity.

• A trait can therefore increase fitness even if it has negative effects on health later in life.

Evolutionary Trade-Off

• A trait can provide an important benefit while also creating a disadvantage.

• Natural selection favors traits that improve reproductive success, even if they have health costs.

• This helps explain why the human body is adapted but imperfect.

Disease

• A statistically subnormal biological functioning for a given species.

• From an evolutionary perspective, disease does not necessarily mean the body is poorly designed.

• Natural selection does not directly "select for disease"; it can instead leave organisms with vulnerabilities to disease.

Why doesn’t natural selection maximize health

• Natural selection primarily maximizes the probability of survival to reproduction.

• There is less evolutionary pressure to maintain perfect health after reproduction.

• Traits that benefit reproduction can persist even if they cause health problems later.

Proximate vs Ultimate Explanations

• Proximate explanations ask how a trait or disease works.

  • What is the mechanism?

  • What is the ontogeny?

• Ultimate explanations ask why the trait exists from an evolutionary perspective.

  • What is its phylogeny?

  • What is its selective advantage?

Ontogeny

• The development of an individual or of a particular anatomical/behavioral feature.

• Examines how a trait develops during an individual's lifetime.

• Example: childhood excess caloric consumption can affect satiety pathways later in life.

Phylogeny

• The evolutionary development and diversification of a species or trait.

• Can involve comparing humans with other related species.

• Helps explain how particular characteristics developed over evolutionary time.

Evolutionary Explanation of Obesity

• Mechanism: excess calories are converted into stored fat.

• Ontogeny: childhood caloric excess can alter brain pathways involved in satiety.

• Phylogeny: humans evolved the ability to maintain substantial fat stores.

• Selective advantage: stored fat provided energy during periods of food shortage.

Thrifty Gene Hypothesis

• Humans evolved mechanisms that encouraged eating and storing calories as fat during periods of food scarcity.

• These mechanisms were advantageous when food was unpredictable.

• In modern environments with abundant food, the same adaptations can contribute to obesity.

• Obesity may therefore reflect an evolutionary mismatch, rather than simply laziness or lack of willpower.

Evolutionary Mismatch

• Occurs when traits adapted to an ancestral environment become disadvantageous in a modern environment.

• Human biology changed relatively slowly while human culture and environments changed rapidly.

• Example: adaptations for surviving food scarcity can contribute to obesity when food is constantly available.

• Helps explain many modern diseases of civilization.

Appetite Regulation and Food Shortage

• Human appetite regulation evolved to help us survive food shortages.

• Food shortages can increase appetite and raise the body's defended weight.

• Dieting can activate similar mechanisms as the body attempts to regain lost weight.

• This helps explain why maintaining weight loss can be difficult.

Food Cravings as an Evolutionary Adaptation

• Humans tend to strongly prefer salt, sugar, and fat.

• These resources were relatively scarce in the environment of evolutionary adaptedness (EEA).

• Seeking calorie-dense foods would have been beneficial when food was unpredictable.

• In modern environments, abundant high-calorie foods can make this adaptation harmful.

Anxiety as an Adaptive Response

• Anxiety and fight-or-flight responses evolved to help organisms respond to danger.

• When triggered appropriately, anxiety can increase the chances of survival.

• When triggered at inappropriate times, the same response can become maladaptive.

• Evolutionary medicine therefore distinguishes between an adaptive response and a disorder caused by its inappropriate activation.

Symptoms as Defenses

• Some symptoms of illness may actually be evolved defense mechanisms.

• Examples include:

  • Fever

  • Coughing

  • Vomiting

  • Diarrhea

  • Pain

• Suppressing a symptom without addressing its cause can sometimes interfere with the body's defenses.

Pathogen Virulence

• Natural selection favors the level of virulence that maximizes a pathogen's reproduction and transmission.

• Pathogens are not necessarily selected to become less harmful.

• The optimal level of virulence depends partly on how the pathogen is transmitted.

Rhinoviruses and Virulence

• Rhinoviruses can spread more effectively when infected people are up and moving around.

• Their transmission is therefore connected to the host's behavior.

• This demonstrates how pathogen evolution can be influenced by the conditions that promote transmission.

Plasmodium and Virulence

• Plasmodium can spread more effectively when its host is relatively sedentary.

Antibiotic Resistance

• Antibiotics create selection pressure on bacterial populations.

• Susceptible bacteria are killed or inhibited while resistant bacteria are more likely to survive.

• Resistant bacteria can then reproduce and become more common.

• This is an example of natural selection occurring in response to human behavior.

Public Health and Evolution

• Public health interventions can change the evolutionary environment experienced by pathogens.

• Improvements such as clean water and sanitation can alter transmission.

• Changing transmission conditions can create selection pressures that favor different levels of virulence.

Paleolithic Genes vs. Postmodern Lifestyle

• Eaton, Konner, and Shostak argue that humans remain broadly adapted to a Paleolithic hunter-gatherer lifestyle.

• Humans evolved over millions of years in environments characterized by hunting and gathering.

• Agriculture, domestication, industrialization, and urbanization dramatically changed human lifestyles.

  • This creates an evolutionary mismatch between our biology and modern lifestyles.

• Cultural change is rapid, while genetic evolution is comparatively slow.

• Our biology may therefore be poorly matched to aspects of modern life.

Diseases of Civilization

• Chronic diseases that became particularly common in industrialized societies.

• Examples include:

  • Obesity

  • Diabetes

  • Hypertension

  • Heart disease

  • Atherosclerosis

  • Some cancers

• Related to the concept of evolutionary mismatch

Paleolithic Lifestyle

• Characterized by greater physical activity and diets that differed from modern industrialized diets.

• Hunter-gatherer diets generally contained:

  • More protein and fiber

  • Less fat and sodium

Diabetes in industrialized populations

• Diabetes was reported as being substantially more prevalent among industrialized Western populations.

• This supports Eaton et. al’s argument about the relationship between Westernization and chronic diseases.
  
  

Atherosclerosis

• Arteriosclerosis: hardening of the arteries.

• Atherosclerosis: a form of arteriosclerosis involving the innermost part of an artery.

• Involves calcified deposits that can narrow or close the blood vessel.

Human Biological Variation

• Refers to differences in biological traits within and between human populations.

• Variation can occur at the:

  • Population level.

  • Group/population frequency level.

  • Individual level.

• Both genes and environment contribute to biological variation.

Population

• A community of breeding partners.

• Defined largely through reproductive relationships.

• Anthropologists examine:

  • Differences within populations.

  • Differences between populations.

  • Commonalities shared by populations.

• Variation can be explained through genes, environment, migration, natural selection, and history.

Polymorphic Trait

• A trait that exists in two or more forms within a population at appreciable frequencies.

• The different forms are called alleles.

• Examples include:

  • ABO blood types.

  • Freckles.

• A trait is considered polymorphic when the less common allele occurs in more than ~2% of the population.

• This differs from a rare trait, which occurs in roughly 1 in 10,000 people.

Causes of Human Biological Variation

• Differences in allele frequencies between populations can result from:

  • Natural selection.

  • Genetic drift.

  • Migration/gene flow.

  • Shared evolutionary history.

• These processes can cause populations to become genetically different over time.

Genetic Drift

• A change in allele frequencies due to random chance rather than natural selection.

• Particularly important in small populations.

• A trait can become more or less common simply because of random differences in reproduction.

Migration / Gene Flow

• Movement of individuals between populations can introduce new alleles.

• This can change the genetic composition of a population.

• Migration can therefore increase or decrease genetic differences between populations.

Tay-Sachs Disease

• A genetic disorder involving the buildup of GM2 gangliosides that damages nerve cells.

• Causes progressive:

  • Loss of muscle control.

  • Seizures.

  • Loss of vision.

  • Mental impairment.

  • Paralysis.

  • Difficulty swallowing and breathing.

• It is inherited through an autosomal recessive pattern.

• The disease occurs at different frequencies in different populations.

Autosomal Recessive Inheritance

• A person must inherit two copies of a recessive allele to develop the condition.

• If both parents are carriers (Rr × Rr):

  • 25% → RR, unaffected.

  • 50% → Rr, carrier.

  • 25% → rr, affected.

• This inheritance pattern explains why a disease can remain hidden in a population through carriers.

Balanced Polymorphism

• An evolutionary state where natural selection actively maintains multiple alleles or distinct phenotypes.

• A harmful allele can remain common because heterozygotes receive an advantage.

  • Natural selection maintains both alleles because the heterozygous condition provides a benefit.

• Tay-Sachs has been discussed as a possible example involving Ashkenazi Jewish populations.

  • Heterozygotes were proposed to have increased resistance to tuberculosis.

Genotype × Environment → Phenotype

• A person's genotype interacts with their environment to influence their phenotype.

• The same genotype can produce different outcomes under different environmental conditions.

• Therefore, biology cannot always be understood by looking at genes alone.

Plasticity

• The ability of an organism to change its biology or behaviour in response to environmental conditions.

• Humans are highly plastic because we are generalists capable of living in many environments.

• Plasticity can occur:

  • Within an individual's lifetime.

  • Across populations exposed to different environments.

• Examples include changes in height, lung capacity, blood characteristics, and metabolism.

Human Plasticity: Height

• Human height can change substantially in response to environmental conditions.

• Dutch males were historically among the shortest Europeans but are now among the tallest.

  • ~5'4" → ~5'10".

• First-generation Mayan immigrants to the U.S. were on average about 2.2 inches taller than Mayans in Costa Rica.

• Better nutrition and health conditions can contribute to increased height.

• This demonstrates that biological characteristics are not completely fixed by genes.

Lactase Persistence

• The continued production of lactase into adulthood.

• Most humans naturally produce less lactase after childhood.

• Some populations maintain lactase production because of a long history of milk consumption.

• Especially common among some:

  • Northern European populations.

  • East African populations.

• Demonstrates interaction between culture, environment, and genetics.

Gene-Culture Coevolution

• Culture can change the environment in ways that create new selective pressures.

• Those pressures can influence genetic evolution.

• Example:

  • Humans begin herding and consuming milk.

  • Milk becomes an important food source.

  • Lactase persistence provides an advantage.

  • Genes allowing adult lactose digestion become more common.

• Culture can therefore change the evolutionary environment.

Why Race Is Not a Biological Proxy

• Human biological variation does not fit neatly into racial categories.

• Variation is generally continuous, rather than divided into discrete racial groups.

• There is often more genetic variation within socially defined racial groups than between them.

• Racial categories therefore cannot reliably predict an individual's genetic characteristics.

• Race can still have important effects on health through social and environmental processes.

Continuous Variation

• Biological traits often vary along a continuum rather than forming distinct categories.

• Example: height has many possible values rather than a few fixed types.

Nonconcordant Variation

• Different biological traits tend to vary independently of one another.

• Having one trait associated with a supposed racial category does not mean a person will have all the other traits associated with that category.

• Example:

  • Skin colour does not reliably predict other physical or behavioural traits.

• Visible traits like skin colour do not correlate with internal or complex traits like intelligence, athleticism, or overall genetic makeup.

Within-Group vs. Between-Group Variation

• A large amount of human genetic variation exists within populations rather than between socially defined races.

• This means two people classified within the same "race" can be genetically quite different.

• People classified into different races can be genetically similar.

The Six Problems With Biological Race

1. The concept assumes fixed biological types.

2. Human variation is continuous.

3. Human variation is nonconcordant.

4. There is greater genetic variation within groups than between races.

5. There is no consistent way to classify people by race.

6. There is no clear agreement about what race actually is biologically.

“Double Error” in Race and Health

• The first error is assuming a difference in disease rates is caused primarily by genes.

• The second error is assuming racial groups have distinct genetic differences that explain those rates.

• Race therefore should not automatically be treated as a genetic explanation for health disparities.

The effect of race on health

• Race itself does not necessarily cause biological disease differences.

• However, being socially classified into a racial group can expose people to different:

  • Environments.

  • Socioeconomic conditions.

  • Healthcare systems.

  • Experiences of racism and discrimination.

Evolution of Human Skin Colour

• Skin pigmentation evolved largely in response to ultraviolet (UV) radiation.

• Humans became increasingly hairless, creating a need for another form of UV protection.

• Different environments created different selective pressures:

  • High UV → darker pigmentation.

  • Low UV → lighter pigmentation.

• Skin colour is therefore an example of adaptation to environment, not evidence of biological races.

Homo ergaster and Hairlessness

• By around 1.6 million years ago, Homo ergaster had:

  • Less body hair.

  • More sweat glands.

  • A body better suited for long-distance walking.

• Increased sweating helped prevent overheating of the brain.

• Once body hair decreased, pigmentation became increasingly important for UV protection.

Folate and Skin Pigmentation

• Excessive UV exposure can break down folate (vitamin B).

• Folate is important for:

  • Fetal development.

  • Reproduction.

  • Sperm production.

• In high-UV environments, dark pigmentation helps protect folate.

• This provides an evolutionary explanation for darker skin near the equator.

Vitamin D and Skin Pigmentation

• UV radiation is necessary for the body to produce vitamin D.

• Very dark pigmentation can reduce UV penetration.

• In regions with low UV, lighter skin allows more efficient vitamin D production.

• Vitamin D deficiency can contribute to rickets.

• This creates an evolutionary trade-off between folate protection and vitamin D production.

Evolutionary Trade-Off of Skin Colour

• Skin pigmentation balances two competing needs:

  • Protect folate from excessive UV.

  • Allow enough UV penetration for vitamin D production.

• High UV environments favour more pigmentation.

• Low UV environments favour less pigmentation.

• Skin colour therefore reflects adaptation to local environmental conditions.

Culture and Skin Colour

• Biology is not the only way humans adapt to UV radiation.

• Cultural adaptations include:

  • Clothing.

  • Shelter.

  • Changes in diet.

• Example:

  • Designing houses with shade.

  • Inuit diets that are reliant on mammal fats and oils (helps with vitamin D).

  • Wearing wide-brimmed hats, turbans, veils to cast shadows on the face.

Migration and Skin Colour

• Human migration exposed populations to new UV environments.

• Skin pigmentation adapted over evolutionary time to local UV conditions.

• Recent migrants may initially experience a mismatch between their pigmentation and their new environment.

• This can increase risks such as:

  • Folate depletion.

  • Vitamin D deficiency.

  • Skin damage.

Determinants of Health

• Health is influenced by much more than medical treatment.

• Important determinants include:

  • Nutrition.

  • Environment.

  • Living conditions.

  • Personal behaviour.

  • Medical care.

• The key question is not only how to treat disease, but what makes populations healthy or unhealthy.

McKeown Thesis

• Thomas McKeown argued that major improvements in health occurred before many modern medical treatments existed.

• Declining mortality was strongly influenced by:

  • Better nutrition.

  • Improved sanitation.

  • Better living conditions.

  • Improved hygiene.

  • Changes in family size.

  • Rising standards of living.

• Medical treatment is important, but it is not the only or always the main determinant of population health.

Prevention vs. Treatment

• Treatment attempts to address disease after it occurs.

• Prevention attempts to reduce the conditions that produce disease.

• McKeown emphasized greater attention to:

  • Nutrition.

  • Environment.

  • Living conditions.

  • Personal behaviour.

  • Preventative measures.

• Population health cannot be improved simply by adding more medical services.

Bioarchaeology

• The study of human biological remains to understand health, disease, and life in the past.

• Researchers can examine:

  • Bones and teeth for pathology.

  • Documentary evidence.

  • Archaeological artifacts.

  • Biological samples.

• Helps reconstruct historical patterns of morbidity and mortality.

Paleopathology

• The study of disease and injury in past populations, especially through skeletal remains.

• Can reveal:

  • Nutritional stress.

  • Trauma.

  • Infectious disease.

  • Degenerative disease.

• Provides evidence about how health changed through human history.

Heirloom Pathogens

• Pathogens that humans inherited from earlier primate ancestors.

• Examples include:

  • Lice.

  • Pinworms.

  • Yaws.

  • Salmonella.

  • Staphylococci.

• These pathogens could affect hunter-gatherer populations even before agriculture.

Zoonotic pathogens

• “Souvenir” pathogens.

• "Diseases that originate in animals and are transmitted to humans.

• Examples include:

  • Sleeping sickness.

  • Tularemia.

  • Leptospirosis.

  • Schistosomiasis.

• Hunter-gatherers could encounter these pathogens through their interactions with animals and environments.

Why Hunter-Gatherers Had Fewer Large Epidemics

• Hunter-gatherer populations were generally:

  • Small.

  • Mobile.

  • Spread over large areas.

• This made it difficult for diseases requiring large, dense populations to persist.

• Diseases such as measles and influenza require enough susceptible hosts to maintain transmission.

• Agriculture and permanent settlements changed this dramatically.

Epidemiological Transition

• Describes changes in the major causes of disease and death as societies and environments change.

• Traditionally involves a shift from:

  • Infectious disease → chronic/noncommunicable disease.

• Different populations can experience different stages simultaneously.

First Epidemiological Transition

• Associated with the development of agriculture ~10,000 years ago.

• Agriculture led to:

  • Larger populations.

  • Permanent settlements.

  • Population density.

  • Animal domestication.

  • Environmental disruption.

  • Increased social inequality.

• These changes increased infectious disease transmission.

Agriculture and Infectious Disease

• Agriculture changed disease ecology by creating:

  • Dense populations.

  • Permanent settlements.

  • More contact with animals.

  • Contaminated water and waste.

  • Greater parasite exposure.

• Reliance on staple crops could also reduce dietary diversity.

• Agriculture therefore produced both nutritional stress and infectious disease risks.

Urbanization and Disease

• Cities increased disease transmission because of high population density.

• Crowded populations allowed:

  • Respiratory diseases to spread.

  • Waterborne diseases to spread.

  • Parasites to spread through waste.

• Trade and travel connected previously isolated populations, allowing pathogens to spread over large geographic areas.

Industrialization and Health

• Industrialization created major environmental and social changes.

• Rapid urbanization often produced:

  • Crowded housing.

  • Poor sanitation.

  • Industrial pollution.

  • Contaminated water and air.

  • Poor working conditions.

• These conditions contributed to diseases such as TB, pneumonia, typhoid, smallpox, and diphtheria.

Second Epidemiological Transition

• Infectious diseases began to decline because of:

  • Improved sanitation.

  • Better nutrition.

  • Immunization.

  • Medical advances.

  • Improved living conditions.

• People lived longer.

• As populations aged, chronic and degenerative diseases became more important.

• This transition did not occur equally across all populations.

Third Epidemiological Transition

• Infectious diseases have not disappeared.

• Some diseases are reemerging while new diseases are appearing.

• Important factors include:

  • Globalization.

  • International travel.

  • Urbanization.

  • Environmental disruption.

  • Deforestation.

  • Climate change.

  • Agricultural development.

  • Breakdown of public health systems.

  • Antibiotic resistance.

Double Burden of Disease

• Occurs when a population experiences infectious and chronic diseases simultaneously.

• Common during epidemiological transition.

Social Inequality and Health

• Social inequality affects access to:

  • Food.

  • Clean water.

  • Sanitation.

  • Healthcare.

  • Education.

  • Safe environments.

  • Economic resources.

• Poverty can create a cycle:

  • Poverty → unhealthy conditions → disease → reduced economic opportunity → continued poverty.

Macroparasitism

• A concept describing how powerful groups can benefit at the expense of less powerful groups.

• Social stratification can allow elites to accumulate resources that improve their own health.

• Helps explain how social inequality becomes part of the disease process.

Medical Ecology

• An approach that views health and disease as reflections of ecological relationships.

• Examines relationships:

  • Within populations.

  • Between populations.

  • Between organisms and their physical environments.

• Health can be understood as a measure of how well a population has adapted to its environment.

Homeostasis

• The maintenance of a relatively stable state of balance within a biological system.

• In medical ecology:

  • Organisms interact with their environments.

  • Different parts of the system are interdependent.

  • These relationships help maintain equilibrium.

• Health is associated with balance/equilibrium.

Disequilibrium

• A state of imbalance between an organism and its environment.

• In medical ecology, disease can be understood as a state of disequilibrium.

• Example:

  • A host encounters a pathogen.

  • The ecological relationship becomes disrupted.

  • Disease results.

Adaptation

• The shaping of biological or cultural traits to fit particular environments.

• An adaptation improves an organism's ability to survive and reproduce in a particular environment.

Maladaptation

• A trait or phenomenon that jeopardizes survival or reproduction.

• Something can be adaptive in one environment but maladaptive in another.

Cultural Ecology

• A microlevel approach examining relationships between people, culture, and the environment.

• Health and sickness are analyzed through the lens of ecological adaptation and maladaptation.

Political Ecology

• Examines how power, inequality, economics, and politics influence human-environment relationships.

• Assumes that environmental resources and risks are not distributed equally.

• Has roots in Marxist theory.

• Goes beyond the local environment to examine larger social structures.

Cultural Ecology vs. Political Ecology

• Cultural ecology:

  • Microlevel.

  • Focuses on local human-environment interactions.

  • Emphasizes adaptation/maladaptation.

• Political ecology:

  • Macrolevel.

  • Examines political and economic structures.

  • Focuses on inequality and power.

  • Considers historical processes such as colonialism, migration, and social stratification.

Sickle-Cell Anemia

• A genetic disorder involving abnormal hemoglobin.

• Red blood cells become sickle-shaped rather than normally shaped.

• Abnormal cells can block blood vessels and cause:

  • Severe pain.

  • Organ damage.

  • Strokes.

  • Early death.

• Occurs when an individual inherits two sickle-cell alleles.

Sickle-Cell Trait

• Occurs when individuals with two different alleles have higher fitness than either homozygous form under certain environmental conditions.

• In sickle-cell populations:

  • AA → susceptible to severe malaria.

  • AS → increased malaria resistance.

  • SS → sickle-cell disease.

• In malaria-endemic environments, the AS genotype can therefore be favoured by natural selection.

Malaria

• An infectious disease caused by Plasmodium parasites.

• Transmitted by female Anopheles mosquitoes.

• Parasites reproduce in:

  • Human liver cells.

  • Red blood cells.

  • Mosquitoes.

• Malaria can create strong natural selection for genetic traits that provide resistance.

Engineering metaphor

• The human body → a machine.

• Optimum health: the body's normal structure and function.

• Disease is treated like a mechanical problem that can be fixed through intervention.

• Physicians act somewhat like mechanics, identifying problems and intervening to correct them.

• McKeown argues that this metaphor can misdirect medical science by emphasizing technological and biomedical interventions while underemphasizing major determinants of health such as environment, nutrition, sanitation, and behaviour.

Sub-fields in Anthropology

• Cultural Anthropology: Studies living human societies, behaviors, and cultural traditions using fieldwork and participant-observation.

• Biological (Physical) Anthropology: Explores human evolution, genetics, biological variation, and non-human primates.

• Archaeology: Examines past human cultures through material remains, artifacts, and structures.

• Linguistic Anthropology: Investigates how language shapes communication, social life, and cultural identity.

Neolithic Revolution

• The transition from primarily hunting and gathering to food production and agriculture, beginning roughly 10,000 years ago.

Culture

• Culture includes beliefs, values, traditions, ideas, and learned ways of understanding and interacting with the world.

• It acts as a lens through which people understand life.

• Humans are cultural beings, so culture influences how people understand:

  • Health.

  • Illness.

  • Disease.

  • Healing.

  • The body.

Sickness

• Sickness refers to unwanted variations in the physical, social, and psychological dimensions of the self.

• Robert Hahn’s definition.

• It can be understood as a perturbation or disruption that causes a person to diverge from their normal baseline.

• Unlike disease, which emphasizes an objective biological condition, sickness encompasses broader dimensions of the person's experience.

Malaysian Agricultural Complex

• An agricultural system associated with tropical forest environments, particularly in Southeast Asia.

• Relied heavily on root and tree crops, including:

  • Yams.

  • Taro.

  • Bananas.

  • Coconuts.

• Different agricultural practices can create different environmental conditions and therefore different disease pressures.

• Agricultural practices could create environments favourable to mosquito breeding, increasing exposure to malaria.

• This connects cultural practices to the selection for sickle-cell trait in populations exposed to malaria.