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Flashcards in Disease Adaptation Deck (25)
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1

What is human ecology?

Human Ecology embraces all the mechanisms
by which humans adjust/react to their
environment to form an interdisciplinary field –
environmental physiology, growth and nutrition,
epidemiology, socio-cultural forces, genetics
and demography

2

What is disease?

-an impairment of health and well-being
- any condition that causes pain, dysfunction, distress, social problems, or death to the person afflicted
-a maladjustment of the human organism to the environment

3

What is health?

-absence of illness, pain or injury
-a state of complete physical, mental, and social well-being

4

What causes disease?

Humoral (hot/cold)
Miasma
Karma
Demonic/Sorcery
Punitive
Germ
Epidemiological Triad
Multifactorial causation
Web of causation

5

Anthropology and the study of disease

● We don’t all get the same diseases
● We don’t all get the same symptoms
● There’s a role for understanding of our biotic and social environments (and histories) in explaining some of this
○ Human biological and social variation
○ Impacts of the physical environment

6

Key concepts and approaches

● Species-level evidence basis for ‘normal’
○ Combatting ethnocentrism with data
● Need for both group- and individual-level explanations
● Our relationship with disease is dynamic not static
● Constraints due to our evolutionary past (evolutionary medicine)
● Trade-offs
○ Adaptability and accommodation (rather than just adaptation)

7

What is stress?

What are we talking about?
Nutritional/Energetic stress
Severe trauma
Psycho-social stress
Short term? Long term? - Seem to be different
Hard to pin down but seemingly important for health outcomes

8

(Pre)Historic perspectives/Evo Med

● We’ve always had contact with infectious life forms
○ Those might have mostly been parasites
● We’ve not always had this much disease
○ We can’t be sure but it seems likely
● Group sizes and mode of subsistence play important roles
○ cities (high population density, sedentarisation), livestock, land clearing
● A lot of what negatively affects our health is to do with changes that have occurred in our environments (broadly defined)

9

Trade offs?

An evolutionary concept
Basically, sometimes we can’t have it all growth vs survival vs reproduction it’s situation-specific, it could be...
● current survival vs future survival
● current reproduction vs future survival
● current survival vs future growth, etc.

10

Trade offs in Ethiopia

Problem: poor access to clean water leads to poor health outcomes (infant mortality) and huge time spent on carrying water
Solution: build wells!
Effect: reduction in infant mortality, shorter birth intervals (both of which mean more children and more competition for food in already impoverished families), thus poorer child health

11

Evolution and infectious disease

Disease is a powerful pathway for natural selection to act

12

The human immune system

Depends on the ability of the body to distinguish self from non-self. Is extraordinarily complex

13

Shared histories with parasites

Parasites and humans have co-evolved
•Natural selection has reduced the virulence of many pathogens (only a small % of microorganisms living in the body cause infectious diseases)
•Some pathogens are specific (have a lifestyle adapted entirely to one host) indicating a long evolutionary history e.g. gonorrhoea
•Humans, however, are constantly changing their environment, and thereby exposing ourselves to new pathogens

14

Schistosomiasis and Humans

First mentioned in Egyptian papyrus dating 1900BC - very specific relationship between Schistosoma, its intermediate Bulinus snail and human hosts

15

Pathogen evolution: strategy

• If a parasite is very virulent it can kill its host quickly, but it will be successful if it has managed to reproduce
• A benign parasite may reproduce more slowly, and leave fewer descendants
• The best strategy depends on the lifespan, and ecology of the host, the symptoms produced and the reproduction of the parasite
• Sometimes parasites are virulent, sometimes they become mutualists

16

Virulence

The ability of a pathogen to cause disease / the degree to which a pathogen causes a loss of fitness in its host

17

Specificity

The degree to which a pathogen can infect a range of hosts

18

Lability

A pathogen’s ability to change, usually down to rapid rates of reproduction (so evolution can occur quickly)

19

How did the common cold get to be
so common?

Labile pathogens constantly change due to rapid rates of reproduction
An important dimension to the success of some pathogens
e.g. common cold, influenza is that they are enormously labile with short generation times, and thus are able to remain a step ahead of the human immune system and antibody production

20

Chronic Non-infectious Disease

Infectious vs non-infectious
-is there an infectious agent involved?
Communicable/non-communicable
-Can it be passed from one person to another?
Acute vs chronic
- short term vs long term, persistent
- not a question of severity or threat to life
Some things straddle the borders of the categories

21

Melanin & rickets: backstory

● Ancestors = possibly no pigment (like chimps)
● Over time we lost hair and got darker skin
● The selective pressure might have been exerted through fetal losses (because of folate)
● As some humans left Africa, females might have struggled with pregnancy and lactation due to falling Vit D levels in body leading to selection for lighter skin
● Agriculture may have aggravated things by reducing nutrition from Vit D rich sources
● Result: humans have different levels of pigment in different parts of the world

22

A History of Disease

-First infectious disease transition
•Agriculture – Dietary shift/ clearing forests
•Settled lifestyles/ - increased population density
•Domesticated animals – contact with animals/zoonoses
•Urbanisation – endemic diseases (common person to person)
-Second disease transition
•Contact between populations
•Virulent epidemics e.g. the black death
-Third disease transition
•trans-oceanic contact with Columbus measles)
-Fourth transition?
● emerging and re-emerging pandemics e.g. HIV, avian flu
-Fifth transition?
● the rise of chronic diseases e.g. CVD, type 2 diabetes

23

Ten leading causes of death (USA)

-Rise in non communicable diseases –in the US
-Infectious diseases that were the most important causes of death at the beginning of the twentieth century have been replaced by non communicable diseases

24

Siberian people and chronic disease

-Very well-adapted to cold (culturally, biologically) USSR changes to modes of subsistence (collectivisation) more access to medical care and food
-Post-Soviet children more undernourished adults more overweight diet poorer quality fewer reindeer herders low lipids, high BP

25

Current limitations to be overcome

● Reluctance to pay attention to socio-political forces
● Difficulty keeping up with understanding changing environments (broadly speaking)
● Human focus dominates rather than One Health
● Hidden influence of values and effects on judgement & blame