Problems of survival (1): Outline

I Hunter-gatherer lifeI mortalityI causes of deathI nutrition

I Darwinian medicineI senescenceI why we get sick

I The behavioral immune systemI disgustI group bias (ethnocentrism and xenophobia)

Staying alive: Life as a hunter-gatherer

We evolved as hunter-gatherers. How was life different?

I higher mortality, different causes of death

I diet of wild foods

I little anonymity; small mobile groups

Mortality as a hunter-gatherer

What does an “expectation of life at birth of 32 years” mean ?

Ache mortality Canada mortality

Mortality as a hunter-gatherer: Causes of death

Differences in causes of death?

I InfectionI !Kung: infection and parasites 70-80% of deaths; Howell

I Trauma

I Efe: 63% health complaints concerned trauma; Bailey

I Violence?

I Ache: cause of death, 15-59 years due to: ((Hill and Hurtado)I violence: 46%I illness: 28%I accidents: 23%I degenerative: 3%

The real paleo diet: Good or bad?

(except the hunter-gatherer is walking, not riding)

Hunter-gatherer nutrition

The good:

I no nutritional deficiencies (mobile, foraging !Kung)

I ↓ sugar, ↓ saturated fat, ↑ fiber

The not-so-good: calorically marginal (!Kung, Ache)

I costs in illness, work

I costs in fertility

Hunter-gatherer birth seasonality

more !Kung children conceived in the “fat time” (Ache similar)

Implications for evolutionary psychology

Strong selection for

I avoiding infection and accidents

I coping with violence

I finding calorie-rich foods

Problems of survival (1): Outline

I Hunter-gatherer lifeI mortalityI causes of deathI nutrition

I Darwinian medicineI senescenceI why we get sick

I The behavioral immune systemI disgustI group bias (ethnocentrism and xenophobia)

Why do we get sick?

I trade-offs

I constraints

I conflicts

I defenses

I smoke-detector theory

I novel environments

Why do we senesce?

Senescence is the deterioration of the body with age.

late-life effects on reproduction and survival have smaller effects onDarwinian fitness than at earlier ages.

Evolutionary theories about aging

deleterious alleles that are expressed at older ages can accumulatethrough mutation and not be selected out (e.g., Huntington’s)

Antagonistic pleiotropy: (pleiotropy = gene that affects more thanone trait)

I a gene positive in youth, deleterious when old

I will selection favor?

I testosterone in males?

I tumor suppressor gene p53 ( too much → aging, too little →cancer)?

Why do we get sick?

I trade-offs (sickle-cell, senescence. . . )

I constraints

I conflicts

I defenses

I smoke-detector theory

I novel environments

Why do we get sick?

I trade-offs (sickle-cell, senescence. . . )

I constraints

I conflicts

I defenses

I smoke-detector theory

I novel environments

Why do we get sick?: Conflicts

Toxoplasmosismakes rats fearless, especially aroundcats!

may affect human behavior also(by-product)

other examples?

Why do we get sick?

I trade-offs (senescence, sickle-cell)

I constraints

I conflicts (rabies, toxoplasmosis in rats)

I defenses

I smoke-detector theory

I novel environments

Why do we get sick?

I trade-offs (senescence, sickle-cell)

I constraints

I conflicts (rabies, toxoplasmosis in rats)

I defenses (coughing, fever, iron-poor blood, anxiety,depression?)

I smoke-detector theory

I novel environments

Why do we get sick?

I trade-offs (senescence, sickle-cell)

I constraints

I conflicts (rabies, toxoplasmosis in rats)

I defenses (coughing, fever, iron-poor blood, anxiety,depression?)

I smoke-detector theory

I novel environments

Why do we get sick?

I trade-offs (senescence, sickle-cell)

I constraints

I conflicts (rabies, toxoplasmosis in rats)

I defenses (coughing, fever, iron-poor blood, anxiety,depression?)

I smoke-detector theory

I novel environments (diabetes, allergies? SIDS? depression?)

Problems of survival (1): Outline

I Hunter-gatherer lifeI mortalityI causes of deathI nutrition

I Darwinian medicineI senescenceI why we get sick

I The behavioral immune systemI disgustI group bias (ethnocentrism and xenophobia)

The behavioral immune system: Disgust

We have an evolved psychology to detect and avoid disease

I disgust: expression in infants associated with bitter taste

I generalized later: what do you find disgusting?

I e.g: feces, rotten food, bodily secretions, signs of illness

I reduced by exposure, culturally modifiable

disgust face: clenched nostrils,squinty eyes, pursed lips:decreases sensory exposure?

The behavioral immune system: disgust and immunity

Exposure to pictures of guns or diseaseincreased immune marker in whiteblood cells (not to threatening stimuliin general). From Schaller et al. 2010

The behavioral immune system: social bias

Does avoiding outsiders reduces exposure to novel pathogens?Looked at:

1. people who naturally felt more vulnerable to disease (q’aire)2. people primed to feel vulnerable to disease

5.00

5.25

5.50

5.75

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6.25

6.50

Accidents Diseases

Salient Threat

End

orse

men

t

Nigerian Immigrants

Scottish Immigrants

Figure2. Interaction between disease salienceand geographical origin of immigrantson endorsement ofpotential immigration (Study5).

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40

45

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60

65

Accidents Diseases

Salient ThreatPe

rcen

tAllo

catio

nof

Fund

s Foreign ImmigrantsFamiliar Immigrants

Figure3. Interaction between disease salienceand foreign-nessof geographical areason allocation ofimmigration advertisingbudget (Study6).

from Faulkner et al.

The behavioral immune system: social bias

does sensitivity to disease lead to in-group bias? (Maybe)

I people who feel vulnerable to disease: more in-group bias

I pregnant women in 1st trimester: more sensitive to disgust

I pregnant women, 1st trimester: more in-group bias

from Navarrete et al 2007

Fig. 1. Intergroupbias andnauseaover thecourseof pregnancy. Thesolidlinedepicts the relativeattraction for theAmerican over the foreign targetacrossweek of pregnancy. Thedashed linedepicts self-reported nausea.

from Fessler et al 2005

Problems of survival Summary

Hunter-gatherers: threats to survival

I high infant and child mortality (but normal lifespan)

I deaths from infection, accidents, aggression (not degenerativedisease)

Darwinian medicine

I senescence due to lower selection at older ages

I illness from an evolutionary perspective: defenses, trade-offs,novel-environments, smoke-detector principle

The behavioral immune system

I disgust: elicited by things that might make you sick

I sensitivity to disease may enhance group bias