ANT208 Lecture 8: Biosocial Interactions and Health Disparities

Communicable diseases (CD): infection, co-evolution, changing environments (Infectious Diseases)

Communicable diseases (CD)

diseases caused by pathogens that can be transmitted between individuals, either directly or indirectly; dynamic systems shaped by evolution, environment, and human behavior, involving continuous interaction between humans and pathogens

CD is preferred over infectious disease

• emphasizes transmission between hosts

  • focuses on spread within populations, not just infection

What is required for a communicable disease to spread

a biological agent (pathogen) that enables transmission

Examples of disease agents

• bacteria

• viruses

• parasites

• fungi

What is a vector

an organism that transmits a pathogen between hosts - mosquitos transmitting malaria

Why are vectors and pathogens important evolutionarily

they are biological organisms subject to natural selection, constantly evolving

How were diseases explained before germ theory

they were thought to be spread through social or environmental factors (ex. bad air or miasma)

What changed with germ theory

recognition that microorganisms (pathogens) cause disease

What is co-evolution int he context of disease

the reciprocal evolutionary relationship between humans and pathogens

• humans evolve immune defenses

• pathogens evolve ways to evade themoh

how has the Human relationship with pathogens changed over time

due to:

• changes in environment

• agriculture

• urbanization

• global travel owh

how does the Anthropocene affect communicable diseases

human-driven changes (climate change, urbanization) alter:

• pathogen spread

• vector distribution

• disease emergence

• ex. warming climates expand mosquito habitats

How are CDs connected to evolution

• pathogens evolve rapidly

• human populations adapt over time

• disease pressures shape human biology

Why are CDs always changing

because of ongoing co-evolution between humans, pathogens, and the environment

What is an infectious disease agent (pathogen)

microorganism that causes disease by infecting a host and exploiting its resources

How are pathogens related to parasites

many pathogens are microscopic parasites; they live in or on a host and benefit at the host’s expense

pathogen vs vector

• pathogen - causes diseases (ex. bacteria, virus)

• vector - transmits the pathogen (ex. mosquitos, ticks)

  • mosquito (vector) → malaria parasite (pathogen)

why are parasites important in human evolution

humans have always coexisted with parasites, shaping our:

• immune systems

• behaviors

• survival strategies

*humans are not separate from pathogens -we are in a constant evolutionary relationship

why aren’t infectious diseases always lethal

humans have evolved adaptations that allow survival

two main types of adaptations to disease

• physiological (inside the body) → immune system

• behavioral (outside the body) → hygiene practices

Role of immune system

detect and fight pathogens inside the body

why is immune system variation important

• individuals have different immune responses

• this variation helps populations survive diverse infections

What is hygiene in an evolutionary/anthropological sense

broad set of behaviors and social systems that reduce disease transmission

• hand washing

• waste management

• city design

• public health campaigns

hygiene vs immunity

• hygiene = outside the body (prevention)

• immunity = inside the body (defense)

Macro-level vs micro-level disease control

• macro - behavior, society, environment (ex. sanitation systems)

• micro - biological processes (ex. immune response)

why is history important in understanding communicable diseases

shows how disease spread is shaped by:

• migration

• trade

• colonialism

• human interactions

how do human movements affect disease spread

movement spreads pathogens to new populations with little immunity (ex. colonization spreading diseases to Indigenous populations)

What was the belief about CDs ~50 years ago; why was it incorrect

they would be eradicated an replaced by non-CDs (NCDs); pathogens evolve rapidly and adapt to new environments and treatmentshy W

Why do infectious diseases evolve faster than humans?

• short life cycles

• rapid reproduction

• high mutation rateCnaW

Can humans completely eliminate infectious diseases

no - but we can control and manage them

Why is preparedness important in infectious disease control

• diseases evolve

• new outbreaks emerge

• past knowledge helps guide future responses

What dies the study of infectious disease reveal about humans

it reflects the interaction between

• biology

• behavior

• environment

• history

• politics

extrinsic mortality

death causes by external factors (ex. infection, environment) that are often beyond individual control

What are biotic risks

risks from living organisms, especially

• pathogens

• parasites

why is infection a major source of extrinsic mortality in humans

because pathogens:

• are widespread

• evolve rapidly

• can be highly lethal

Key tradeoff in exposure to pathogens

• too much exposure → risk of death

• too little exposure → weak immune system

*immune system needs early-life exposure to develop properly

Why are infants especially vulnerable to infection

their immune system is not fully developed yet

How is the immune system similar to the brain

both require early-life stimulation and development to function optimally

How can the immune system itself become a problem

it can cause autoimmune diseases when it attacks the body’s own tissues (ex. inflammatory bowel disease)

Why might autoimmune diseases be more common today

due to reduced exposure to pathogens in cleaner (high-hygiene) environments

What is the trade-off related to hygiene

• high hygiene → fewer infections

• but → less immune system “training”hW

Why is some exposure to pathogen beneficial?

helps build immune resilience and proper immune regulation

When is infection risk especially high

in environments with

• poor hygiene

• limited health education

• high parasite presence

• weak healthcare systems

how does infection shape human life history

• increases early life mortality risk

• drives evolution of:

  • immune systems

  • caregiving behaviors

main takeaway about infection and human adaptation

humans evolved to balance a trade-off between pathogen exposure and immune development, where both too much and too little exposure can be harmful

why is predation a low source of mortality in humans

humans are apex predators, and no species has evolved to specialize in hunting us

when does predation on humans occur?

occasionally from large mammalian carnivores

• rare and not a major evolutionary pressure on modern humans

Competition as a source of extrinsic mortality

conflict over:

• food

• resources

• mates

why is competition especially important in humans

humans often compete violently, including:

• war

• resource hoarding

• social inequality

Why is conflict one of the biggest modern health problems

it causes both

• direct deaths (violence)

• indirect deaths (system collapse)

how does conflict indirectly increase mortality

• destroying healthcare systems

• causing famine (food control)

• displacing populations

• increasing infectious disease spread

Why do infectious diseases increase during conflict

• poor sanitation

• crowding

• breakdown of healthcare infrastructure

  • ex. cholera outbreaks

  • increased HIV transmission

Who is most affected by competition and conflict

individuals facing structural inequities (poverty, lack of access to care)

How has competition changed over time?

• small scale societies → less large-scale conflict

• state-level societies → more organized, large scale conflict

why is competition considered a major driver of mortality today

because human behavior (violence, inequality) amplifies its effects

what are the main causes of injury-related mortality

• accidents

• violence (*conspecific - human on human)

how does human sociality affect injury rates

• reduces injury through cooperation and care but increases injury during conflict

how do human child rates compare to chimps

• humans - 20-3o%

• chimps - 75%

why do humans have lower mortality rates

• shared caregiving and social systems

how are competition and injury related

conflict → increases injury and mortality

how do predation, competition, and injury compare to infectious disease

infectious disease = highest risk

competition and injury = moderate

predation = low

adaptive systems in humans

biological and behavioral systems that help us survive and reduce mortality risks

what is somatic repair

the body’s ability to heal and restore itself after damage

Examples of somatic repair

• healing after childbirth

• recovery from injury

• repair from nutritional stress

what limits somatic repair

• severe injury

• aging (senescence)

role of immune system

detect and eliminate pathogens inside the body

how does immune defense relate to survival

primary defense against infectious disease, the biggest mortality risk

what is the near-endocrine threat response

the fight-or-flight system that responds to immediate danger (ex. touching a hot pan and pulling away)

what hormones are involved

• cortisol - primary stress hormone, increases blood sugar and suppresses non-essential functions to sustain energy

• adrenaline - instant energy, increasing HR and alterness

Why is neuroendocrine threat response adaptive

allows rapid reaction to threats reducing risk of injury or death

what is social coordination

organizing into groups for cooperation and protection

how does grouping reduce mortality

• protection from predators (ex. being in a group reduces risk of being attacked)

• shared resources

• reduced infection exposure

Major downside of social coordination

exclusion and “othering” (*adaptive behavior can become socially harmful if exaggerated)

othering

treating outsiders as different or dangerous, often leading to exclusion (ex. isolation of individuals with diseases)

theory of mind

ability to understand and predict others’ thoughts and intentions

Why is theory of mind adaptive

it helps with:

• cooperation

• conflict resolution

• planning strategies

how is the human brain an adaptive system

it allows

• anticipation of threats

• complex social strategies

  • problem-solving

how do the body systems work together

• somatic repair - fixes damage

• immune system - fights infection

• neuro-endocrine - responds to threats

• social systems - prevent risks

CDs vs NCDs

• CDs - caused by infectious agents and can spread

• NCDs - not caused by pathogens and are not transmissible

Infection vs Disease

• infection - presence of microorganism in the body

• disease - when that infection causes harm or symptoms

subclinical infection

an infection that is present but causes not noticeable symptoms

are all parasites harmful

no - some can be benign or beneficial

continuum of host-microbe relationships

• pathogen → parasite → commensal → symbiont

  • pathogen causes harm

  • parasite benefits, host is harmed

  • commensal - benefits, host is unaffected

  • symbiont - both benefit

• ex. gut microbiome organism may have evolved from harmful ancestors

why don’t all pathogens kill their host quickly

because they need the host to survive long enough for transmission

fast-acting vs slow-acting pathogens

• fast = highly contagious, may kill quickly

• slow = persist longer, case gradual damage

Germ theory

the idea that microorganisms cause disease; provides framework to link specific pathogens to diseases

what are Koch’s Postulates used for

identify whether a microorganism causes a specific disease; defines a CD

What are the four postulates (Koch)

1. pathogen is associated with disease

2. can be isolated and grown

3. causes disease in a. healthy host

4. can be re-isolated from the infected host

limitation of Koch’s postulates

don’t account for asymptomatic or subclinical infections

why aren’t pathogens the only factor in disease

disease also depends on host condition and environment

• a person can carry malaria but only get sick under stress (ex. altitude, exertion)

Why do new pathogens tend to be more harmful

hosts are less adapted, so damage is greater

In what ways are humans similar to pathogens

humans can act like ecological disruptors:

• exploit environments

• deplete resources

• move to new areas

why are some diseases more stigmatized than others

due to:

• social beliefs

• historical context

• associations with behavior

*ex. HIV/AIDS has historically been more stigmatized than malaria

Are all pathogens equally important

no - a small number cause most illness and death

• malaria

• tuberculosis

• HIV/AIDS

• Influenza

• Measles

why are some infectious disease re-emerging

• vaccine hesitancy

• changing environments

• pathogen evolution

What are major categories of infectious disease

• respiratory (lungs)

• gastrointestinal - food or touch

• parasitic (worms/helminths)

are medical categories of disease always clear cut

no - there is often a gray area between health and disease

importance of distinguishing between pathogen groups

different pathogens require different treatments and prevention strategies

viruses

infectious agents that replicate inside host cells (pox, influenza)

Why don’t antibiotics work on viruses

antibiotics target bacterial structures, which viruses do not have

how are viral infections controlled?

• immune system

• vaccines