Is Religion Adaptive?€¦ · Feral goats on Rum. Back To The Beginning ... illness rates in...
Transcript of Is Religion Adaptive?€¦ · Feral goats on Rum. Back To The Beginning ... illness rates in...
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Is Religion Adaptive?
Integrating cognition and function
Robin DunbarBritish Academy Centenary Project
Institute of Cognitive & Evolutionary Anthropology
University of Oxford
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Two Evolutionary Questions about Religion
Nothing as costly as religion could possibly be a maladaptation or a mere by-product
• What does [did] religion do for us?
• Why did religion [apparently] evolve only in humans?
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Four [Traditional] Functions for Religion
• gives coherence to a complex world [Freud]
• psychological wellbeing
• social bonding [Durkheim]
• enforces conformity
[moral codes] [Marx]
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Does Religion Benefit You?
Frequent claims that religion has no adaptive benefits at the individual level notwithstanding...
Compared to others, actively religious people:
• live longer
• are more content/happier
• are less stressed
• suffer fewer psychological problems
• recover faster from surgery
[Data from extensive sociological and
epidemiological studies in past decade]
BUT, even if none of these was true….
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The World of Multilevel Selection• Multi-level social systems are common in
mammals• When sociality involves an implicit social
contract….Fitness accrues at the level of the individual, but through benefits generated by the group
• It requires a more subtle understanding of fitness – Hamilton‟s original concept [neighbour-modulated fitnesses]
• This is NOTgroup selection
Elephants at Amboseli
Human social networks
scale hierarchically
Old World monkeys
Feral goats on Rum
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Back To The Beginning….
• Social Brain Hypothesis
• An explanation for the evolution of large brains in primates
• Evidence: group size [and many aspects of “smart” behaviour] are a function of neocortex volume
Apes
Dunbar 1992, 1998
Neocortex ratio = neocortex vol/rest of brain
[i.e. “thinking” part of brain]
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Humans and the Social Brain
• Predicted group size for humans is ~150
[Dunbar‟s Number]
…BUT primate societiesare very intimate
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HumanSocial Groups
All these have mean sizes of 100-200
Neolithic villages 6500 BC 150-200 Modern armies (company) 180Hutterite communities 107„Nebraska‟ Amish parishes 113business organisation <200ideal church congregations <200Doomsday Book villages 150C18th English villages 160GoreTex Inc‟s structure 150Research sub-disciplines 100-200
Small world experiments 134Hunter-Gatherer communities 148Xmas card networks 154
Maximum Network Size
350-374
325-349
300-324
275-299
250-274
225-249
200-224
175-199
150-174
125-149
100-124
75-99
50-74
25-49
0-24
Nu
mb
er
of
Ca
se
s
10
9
8
7
6
5
4
3
2
1
0
“Reverse”Small World Experiments
Killworth et al (1984)
1
10
100
1000
10000
0 10 20 30
Hunter-Gatherer Societies
Dunbar (1993)
Xmas Card Networks
Hill & Dunbar (2003)
Individual Tribes
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The Freerider Problem
Barrett, Dunbar & Lycett: Fig 9-6
0
2
4
6
8
10
0 2 4 6 8 10 12
Coalition Time
Searc
h T
ime
Freeriders are not
successful
T = 0%
T = 25%
T = 100%
Freeriders
are
successful
Enquist & Leimar (1993)
All primate societies are based on animplicit social contract [cooperation]
All such systems are susceptible to freeriders
Dispersed social systems are especially susceptible
Punishment [stick] has attracted mostattention...
BUT it’s only as effective as thedetection rate
Voluntary commitment [carrot] ismuch more effective
Barrett, Dunbar & Lycett: Fig 9-9
0
20
40
60
80
100
0 5 10 15 20 25 30 35
Number of Generations
Fre
eri
de
rs (
% o
f P
op
ula
tio
n)
50%
30%
10%
Rate of dialectic change per generation
Nettle & Dunbar (1997)
Freeriders very
quickly drive
cooperators to
extinction
Freeriders are more successful
over a wide range of conditions
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The Twin Pincers of Primate Sociality
• The intensity of intimacy
• Mentalising [understanding other‟s minds]
1st 2nd 3rd ....order
The Levels of Intentionality
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The Intensity of Intimacy
• Social bonding primate-style
• Intimacy influences trust and obligation
• Grooming increases with group size
• Grooming releases endorphins and creates an opiate “high”
Group Size
160140120100806040200
So
cia
l T
ime
(%
)
50
40
30
20
10
0
Predicted for Humans
Mean grooming
time vs mean
group size for
individual primate
species
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Grooming Time in Humans?
• Grooming as the bonding agent in primates
• Grooming time is a linear function of group size
Group Size
160140120100806040200
So
cia
l T
ime
(%
)50
40
30
20
10
0
Predicted for Humans
Actual
social
time in
humans
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Three Ways to Bridge the Gap?
Millions Years BP
3.53.02.52.01.51.0.50.0-.5
Pre
dic
ted G
room
ing T
ime (
%)
50
40
30
20
10
Laughter
a cross-cultural trait
shared with chimpanzees
Singing and dancing
Religion and its rituals
Australopiths
Modern humans
H. erectus
Archaic humans
The
Bonding
Gap
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Laughter… the Best Medicine?
0
0.5
1
1.5
2
2.5
3
3.5
4
Strangers Acquaintances
Cooperation(in GBP)
Neutral
Comedy
Ss were more generous to strangers
(but not “friends”)
after watching a comedy video
In a Public Good Game P=0.559 p<0.001
Procedure:
pain test – video/activity – pain re-test
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Musical Endorphins
Procedure:
pain test – activity – pain re-test
Musical performance
facilitates endorphin
release, but listening
to music
does not
Dunbar, Kaskatis, MacDonald &
Barra (submitted)
Singing Drumming Dancing Listening
to music
Sing/No sing
Drum
circle
music
shop
video
Fast
Slow
Dance
group
Music
practice
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An Opium for the Masses?
Religious practices are often well suited
to stimulate endorphins
Stigmata of
Padre Pio
Ecstatic states:
make you relaxed
enhance sense of
communalityMedieval flagellants
Whirling dervish
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So, why not get your kicks on your own?
….because creating a sense of
“bondingness” [commitment to
community and prosociality] requires
doing it together [i.e. interacting]!
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Synchony Ramps up the Endorphins
Alone Group Alone Group
Change in pain threshold
before and after 45 mins
rowing work-out on
ergometers in the gym:
Alone vs in a virtual boat
Cohen et al (2008)
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Why Does Religion Have This Effect?
There are two likely mechanisms:
• direct influence of endorphins [endorphins seem to “tune” the immune system]
• sense of belonging and communality acting directly OR indirectly through support from network members
Mean Relatedness in Plymouth Colony
(winter 1620)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Survived Died
… being a member of a large
kinship group reduces
(1) illness rates in children
[Newcastle and Trindad]
(2) death rates in adults
[the Mayflower colonists
in 1620 and the Donner
Party of 1846]
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The Transcendental Edge…?
Sosis & Alcorta (2003)
Something about a transcendental dimension
raises commitment to the project
C19th US utopian cults
Religious cults last longer than secular ones
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The Ecology of Community Size
• Small communities in the Tropics, larger ones at higher latitudes
• Religion density and collectivism are a function of disease prevalence [aka latitude]
Fincher & Thornhill (2008)
Fincher et al (2008)
Barrett, Dunbar & Lycett: Fig 13-4
-7
-6
-5
-4
-3
-2
-1
0
0 2 4 6 8 10 12
Mean Growing Season
Lo
g R
esid
ual N
um
ber
of
Lan
gu
ag
es
Nettle (1999)
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Cults are a Small-Scale Phenomenon
• Foundation size for C19th US utopian cults
• Against expectation (scale-free effect from Zipf‟s Law), N<30 is uncommon, and 150>N>400 is the most common
Dunbar & Sosis (in prep)
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Is There an Optimal Cult Size?
• Very small and very large foundations don‟t survive well
• Optimum size ~150
• For secular communes, optimal size may even be smaller (~50)
50
Dunbar & Sosis (in prep)
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The Role of Social Cognition
• Intentionality as a reflexively hierarchical sequence of belief states
• …that may be very costly in information processing terms
Level of intensionality
9th8th7th6th5th4th3rd2nd1st
Fre
quency o
f fa
ilure
20
10
0
Level of intensionality
1086420
Clique s
ize
30
20
10
0
Kindermann et al (1998)
Stiller & Dunbar (2007)
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Religion at the Limits of Cognition…?
Belief as a personal phenomenon“I believe that God wants us to act
with righteous intent” [3]
Belief as a social phenomenon“I intend that you believe that God
wants us to act with righteous intent” [4]
…. BUT why should you care?
Belief as a communal phenomenon:“I intend that you understand that we believe that
God wants us to act with righteous intent” [5]
Level of intensionality
9th8th7th6th5th4th3rd2nd1st
Fre
quency o
f fa
ilure
20
10
0
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0 1000 2000 3000 4000 5000 6000
Frontal Lobe Volume (cc)
1
2
3
4
5
Ac
hie
vab
le In
ten
tio
na
lity
Lev
el
Monkeys
Apes
Humans
Dunbar (2003)
Why is Religion Unique to Humans?
• If achievable level of intentionality really is determined by capacity of frontal lobe…
• …only humans have sufficient capacity for 5th order
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Can We Date the Origins of Religion?
• Maybe….
• If we can estimate frontal lobe volume from cranial capacity…
…then we can estimate achievable level of intentionality
0
1
2
3
4
5
6
0 200 400 600
Frontal Lobe Vol. (cc)
Ach
iev
ab
le I
nte
nti
on
ali
ty
0.00 1.00 2.00 3.00
date (millions of years BP)
300.0
600.0
900.0
1200.0
1500.0
1800.0
cc
0 200 400 600 800 1000 1200 1400
Total Brain Volume (cc)
0
200
400
600
800
1000
Fro
nta
l L
ob
e V
olu
me
(c
c)
Cranial volume
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Dating the Origins of Religion
• Sufficient frontal lobe volume appears very late
• … not earlier than the appearance of Homo sapiens
[Don‟t get too excited about the Neanderthals] 0
1
2
3
4
5
6
7
0 2 4
Million of Years Ago
Ach
ieva
ble
In
ten
tion
alit
yAustralopiths
H. erectus
Archaic humans
Modern humans
Neanderthals
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Conclusions
• Social contract societies risk collapse from freeriding unless mechanisms are in place to enforce social cohesion
• In primates, this involves both cognitive and psychopharmacological mechanisms
• Voluntary commitment [carrot] works better than punishment [stick]
• Religion and ritual seem to function in just these ways
• Religion is: a small scale phenomenon, very susceptible to fragmentationwell designed to reinforce
in-group/out-group effects [Durkheim was basically right]
• Other benefits are by-products
• Religion may be a very recent evolutionary phenomenon