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Is Religion Adaptive?
Integrating cognition and function
Robin DunbarBritish Academy Centenary Project
Institute of Cognitive & Evolutionary Anthropology
University of Oxford
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?
Four [Traditional] Functions for Religion
• gives coherence to a complex world [Freud]
• psychological wellbeing
• social bonding [Durkheim]
• enforces conformity
[moral codes] [Marx]
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….
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
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]
Humans and the Social Brain
• Predicted group size for humans is ~150
[Dunbar‟s Number]
…BUT primate societiesare very intimate
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
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
The Twin Pincers of Primate Sociality
• The intensity of intimacy
• Mentalising [understanding other‟s minds]
1st 2nd 3rd ....order
The Levels of Intentionality
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
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
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
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
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
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
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]!
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)
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]
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
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)
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)
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)
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)
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
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
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
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
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