Theory of Foragers, Networks, and the Evolution of Cooperation
AAA Session on Kinship
San Francisco, Nov. 2012
Doug White and Tolga Oztan
24 slides
Irvine Social Science Gateway (SDSC)
Kinsources, Project Simpa (French NSF)
Core concepts:
Structural cohesion
Pairwise cohesion
Clues & Data (Binford 2001)
We measure structural cohesion in kinship networks from actual
genealogical data, looking at the variable of structural endogamy.
This variable does not predict level of cooperativity for foragers. WHY
Unless foragers have extensive marine resources & trade, which go hand in
hand as in the Northwest Coast, their population density is usually light.
At these light densities, and with 5-person average nuclear family size (outside
Australia, 6.8), their kinship networks are often low in cohesion.
e.g., Inuit societies, whose resource base stretches over large distances,
have very low intra-community endogamy - spouses are often from
distant communities. This provides little local marriage cohesion.
Instead of marriage ties as a means of integration, in a maximal sample of 34
forager societies for which we have data, we find that kinship and affinal
roles play a major role in creating both cohesion and cooperation. The
idea here is pairwise cohesion.
Table 1 combines Binford's forager population density data with stereotyped kinship roles
coded by Murdock to show the importance of AFFINAL JOKING RELATIONS that are key
to forager reproductive success because joking and license open pathways to
sexuality among in-laws, i.e., pairwise cohesion. Parental in-law avoidances help
indirectly to reduce conflicts of interest such as whether to marry a wife's sister.
Table 1: below the packing threshold there are many more foragers with inlaw Joking and with more types of in-law joking ( !Kung upper left an outlier).
Vertical red line =
Packing density threshold at 9.1 people/kmsq at which
there is no longer unoccupied space into which mobile
hunter-gatherers could move (Binford 2001).
Horizonal red line = crossover to 0 or singular joking pair
Crossover 2x2 Fisher exact test p=.005
3
Table 2: population density with a packing threshold at 9.1 people/km2
is differentially related to Joking relations versus Avoidances (p=.008)
Joking high at low density & decreases
at higher densities p=.005, with
Avoidance more uniform with density.
All 34 societies have Joking or Avoidance,
triangularly limited due to the limited
number of kintypes.
4
Forager Cooperation: Binford 2001
Binford (p.469): “Below the packing threshold, hunter-gatherers are organized so
that all participating individuals have maximal access to the vital resources that are
accessible in their subsistence ranges. Participation in an economically integrated
group means that all individuals endeavor to minimize the risk and maximize the
return from cooperative labor that is directed toward obtaining the vital resources
needed to sustain the group as a whole.”
Sharing among near and distant kin “is very common among hunter-gatherer
groups that have not approached the packing threshold, as is the practice—when
necessary—of using tools and supplies that belong to other persons.” There are
“kin conventions extending food procurement rights to distant kinsmen,” –
including Joking cooperativity – rights that “tend to disappear” above the
packing threshold.
Cooperation is based on indirect reciprocity and easily emulated reputations.
Children are taken by their family members to learn the skills of related kin.
Differentiation is valued rather than competition. Cooperation is locally clustered,
with pairwise chains. Its genesis is easily simulated in a distributed network with
cooperative reinforcement based on reputation.
5
Simulations: What kinds of (kinship) networks do foragers have?
© Helbing, Dirk. 2012. Social Self-Organization]. Springer Berlin. Chapter 14. Systemic Risks in Society and Economics] 285-299
Fig. 14.10 Establishment of cooperation (blue squares= cooperators, red =
defectors/cheaters/free-riders). In a world with local interactions and
local mobility (left) in comparison with the breakdown of cooperation
(right) in a world with global interactions and global mobility (Helbing
p140). The loss of solidarity results from a lack of neighborhood
interactions, not from larger mobility. (see also Boorman and Levitt 1980 Chs. 2-5.
The Genetics of Altruism. NY: Academic Press) For Dawkins and Nowak, Prisoner's
Dilemma and Defection is the Universal Norm.
6
How Joking and Avoidance intermesh is illustrated by the
Tenino trading network, with Joking relations as cooperative
glue and Avoidances reducing conflict
The Tenino are foraging traders at the gulf of the Columbia River. In the sample of 34, including
Tenino, the six foragers groups with Br/Si Avoidance are predicted at p=.01 by “Fishing” as the
regressor. The other 5 foragers are also central
in trade networks.
7
These foragers were the major trading society at the mouth of the Columbia
River. Tenino brothers-in-law (WiBr/SiHu) form chains of trading partners
with special privileges; e.g., borrowing property and returning something
of lesser value. Chains of brothers-in-law operated the trading routes.
WiBr's daughters were also “Joking” relatives, could pass intimate
information; one jokes with WiBr's sons. WiBrDa, Da of a trade partner WiBr,
is “intimate but not sexually” with the FaSiHu trade partner. Between siblings-inlaw of opposite sex—BrWi & SiHu, “intimacy” occurs, even sexual intercourse.
(Murdock 1965). Formal kin-type expectations for Joking relatives generally
promote marriage and cooperation through affinal ties.
Tenino Brother and Sister reinforce trade-link cooperation with an avoidance
relation: they cannot even sit together or talk. WiBrWi is “like” a prohibited sister
and also entails that Br/Si avoid each other. By avoiding WiBrWi there is no
possibility of jealousy between WiBr and SiHu, the Tenino trade partners.
WBW avoidance is more widespread than Br/Si avoidance. Br/Si → WiBrWi is
an entailment!, showing that kinship cohesion is not always based on family tie
“extensions” (Murdock, Shapiro etc); sibling is not an extension of affine.
8
Interpreting these clues
The UNIVERSALITY of Joking and/or Avoidance in our 34-forager
sample IS A GOOD INDICATOR THAT THESE STEREOTYPED KIN RELATIONSHIPS
WERE PRESENT IN PROTOTYPICAL FORAGER SOCIETIES. THESE “REGULATORY
KIN BEHAVIORS” MIGHT HAVE BEEN COMMON EVEN BEFORE THE ADVENT OF
LANGUAGE. Joking links potential marriage partners and their siblings in an explicit
means of cooperation within generations and often an expression of grandparental
support rather than sexuality.
The more extended networks of populations that surpass the packing density contain
more non-kin, and Avoidances surpass Joking to provide indirect broadening of
cooperation by means of conflict resolution between such potential marriage
partners as siblings-in-law or same-generation links through chains of siblings-inlaw, as with the TENINO.
Avoidances manage potential conflicts associated with Joking
relations over sexual access. As management relations
they have precisely interlocked structures, shown the
next 'co-occurence and entailment' graphic.
Four-Dimensional
Dual Lattice
isomorphic with the
data: 100% fit
Hu's Mo
Hu's Fa
Wi's Fa
Wi's Mo
Wife's BrSi
Wife's Br
femMoBr
manFaSi
Hu's Sister So
Hu's Sister
Kin Avoidances
DRW(1995) “Kin avoidance entailments worldwide across kin types.” E.g., Br/Si entails → WiBrWi,
which goes against the universal nuclear family “extentionist” theory (WiBrWi a superset over Br/Si).
The entailments hold for foragers. Bottom to top co-occurrences are rare to frequent; top to bottom
cases, frequent to rare.
10
Kinship Data as a DAG (Dir Asym Graph):
Basic kin-net kinship networks: Nodes are parents, edges are gendered individuals
THIS HELPS US LOOK AT COHESION THROUGH MARRIAGE ALLIANCE
Here, married individuals are a single node but link up to separate parents
Kin-net graphs constructed from standard
genealogies or GED files, using PAJEK or a
number of other programs.
`
Femal
e edge
Marries
her MBS
FaFaSiDaSo
Male
edge
This type of graph allows us to study
cohesion in kinship networks. It has no
k-components with k > 2, hierarchically
embedded
Coefficients of biological relatedness ri,j
and pairwise cohesion ki,j can be coded
in matrices or graphs with individuals as
edges.
no time? cut to 18
11
This is the Agta genealogy made by Oztan, 7+ generations from the 1940s to the present,
87.0 people/km2 (9 times the density threshold). The structurally cohesive marriages are
shown in yellow. Binford classifies this as “a mutualist group that exchanged labor and forest
products with their neighbors in return for agricultural products.” Young women often
married non-Agta men who acquired rights in Agta land. Here, 100% of these (n=49) come
from parents in the (yellow) bicomponent (p=.0007), unlike many agricultural societies
where marginal women marry out. The “mutualist” marriages are at the center of the
society in the assimilation period.
DRW(1995)
12
Hypothesis: Among the !Kung (6.6 p/km2), are bicomponent (yellow) nodes more
likely “cooperators”? (among questions being explored by Oztan: maybe no!)
“Genealogical levels”
(This and the five next slides show various ways of viewing structural cohesion)
Just flip thru these quickly
13
Cohesive kinship networks are bicomponents with egalitarian structure (conducive
to low bullying). Incoming-arrow to parents, outgoing from children, dotted line for
daughter to parents, solid lines son to parents
Rarely a tri- or higher k-component:
Here again: !Kung san (Kalahari
desert). Red lines cut
the
cohesiveness.
“Layout
(arrows to parents)”
Degree centralities are also distributed:
no time?
14 cut to 20
!Kung band-wise kinship p-graph
solid lines male, dashed lines female, arrows point to parents
“Camps”
(Oztan) Research questions, e.g.: How do usufruct rights in
resource clusters map onto kin ties, marriage and movement
between groups, and band memberships?
15
This is the band-level pattern of !Kung Marriages (crosssided = Joking and Avoidances)
“Pairs of Camps”
!Kung Marriages have too little density of
offspring to form many cohesive cycles 16
But !Kung Joking and Avoidances and local “sides” are
ordered purely by the ego role-pattern
“Egocentric”
ego
17
Using graph theory cycles to measure cohesion between sides as a
possible predictor of cooperation in a foraging society (!Kung – result is
similar if females form the sides, men the links)
“Sides” e – n + 1 = No. of cycles
128 – 118 + 1 = only 11! - 5/11 are not sided, tho this looks like twosided marriages the sides are random. Within generations it is joking relatives across-sides that
generate pairwise cooperation. How Joking behaviors create cooperation between brothers-inlaw is further exemplified by the contrast with Pul Eliya farmers, with more children and
population density.
18
Pul Eliyan Sidedness (P-graph): brothers in-law Joke and cooperate, siblings compete over
inheritance of land and irrigation resources passed to son or daughter; gender ambiguity in sides.
This is not random; 146edges -103nodes+1=44 cycles with 8 “errors” (p=.002). But this network is
almost perfectly 2-sided for marriages of those with common ancestors (this can be seen visually in
the 77 red lines within generations between sides).
Can you spot the “wrong marriage”?
Foragers are not dense enough to have this level of cohesive sidedness
19
structural cohesion as a measurement concept:
Moody and White 2003
Menger’s 1927 theorem for a pair of isomorphic network measurements:
(1) Maximal subnetwork with no less than a (min) k-node separator cut  equals
(2) Maximal k-cohesive subnetwork with a minimum number k of node-independent paths
between any x, y pairs of nodes  isomorphic with above (hard proof)
Was a hard/slow algorithm (new work has made it a fast computation)
Red line in the graph: node cut of 3
separating the graph into 2 parts
(this graph is 3-cohesive)
Recent studies show that low structural cohesion (2-3) in school-friendship networks
are egalitarian; high structural cohesion (4-7) precipitates bullying.
Our measure of kinship structure is low-cohesion; piling on of other linkages may
become high-cohesion
20
Cohesion and behavior 3rd-4th grades
Links= self reported friendships
classes with egalitarian (low-k)
classes with hierarchical (hi-k)
cohesion have little bullying,
cohesion have bullying,
bullies liked,
aggressors unpopular
<--(no class size effect)--> victims unpopular
All: aggression corr. with popularity but
neg. corr. with social preference.
All: victimization neg. corr. with both pop.&pref but not corr.21
with aggression
UC Davis Faris & Felmlee bullying study: school-wide
Links= self reported
friendships
12th
green
9th
11th
yellow
8th blue
scattered
N ~ 6-700 more
bullying within
grades than
between
10th
orange
10th
dark
orange
Better interpretation in
the next slide where
variance is examined
http://vidi.cs.ucdavis.edu/projects/AggressionNetworks/
22
Summary of a Network Theory for Evolution of Cooperation among Foragers.
D.R. White & Tolga Oztan 2012.
*Definitions are given in the discussion.
(1) The perspective, evidence and simulation given here lead to a novel
conception of human evolution as emerging from generalized cooperativity
among archaic and later foragers, at variance with an intrinsic selfishness
thought to imply universal competitive gaming, as Dawkins and Nowak suggested.
(2) In general, for friendships, political & corporate alliances, growth of successful
family groups, and, in kin groups--residence, inheritance and lower outmigration--,
groups identified by structural cohesion* show consistent side effects not
replicable by other measures. White et al. citations.
(3) Forager evolution benefited from large brains, recognition of extensive biparental kinship networks, and of marriage within the group, i.e., .structural
endogamy (technically, 2-cohesive or bi-connected* networks of kinship). But
forager population density is often so low -- !Kung 6.6pl/km2, 21 Inuit average
2.4pl/km2 (Binford 2001)-- that stru-cohesion may be insignificant, with too few
effective cycles.
(4) Foragers at low densities have small tightly kin-integrated groups (family,
band, composites of bands) with near-universal access to resources and use-rights
mediated through kinship roles. Reputation for generosity is the basis for prestige
and attempts at leadership domination are punished. Children acquire skills
introduced by kin with diverse abilities and knowledge. Binford 2001.
23
(5) Stru-cohesion provides a basis for forager cooperation, augmented by pairwise
k-cohesion* between ancestors with many children (White & Oztan), while
stereotyped kinship roles (Murdock) such as Joking relations* can facilitate a
direct basis for cooperation that is either group-extended, as between two
subgroups marrying reciprocally, or as extended along chains, e.g., in trade
partnership circuits. Within-generation cooperation is a common result of
such role structures.
(6) A second type of stereotyped pairwise roles that ameliorate potential kinship
conflicts are those of Avoidance* of parents-in-law (which reduces conflict and
loosens access to within-generation spouses) or Avoidance in WiBrWi and in
Br/Si dyads (when siblings-in-law transitivity is at risk, e.g., in trader-circuits).
(7) The great majority of foragers worldwide utilize these various mechanisms to
facilitate cooperation, and have done so in the past. Below the forager packingdensity threshold (9.1/km2)*, Joking is most frequent, and declines with population
density; while Avoidance is less frequent, and increases with population density.
Both eventually decrease as complex societies develop with higher population
densities.
(8) As complex societies develop with high population density, local kinship
networks may densify due to greater numbers of children, and as other nonkin relationships develop with high structural levels of cohesion, often marked by
bullying others, success in defense of the group, and new conflict-avoidance
mechanisms.
24
NOTES
Agta population densities (Binford 2001: 118) are:
Casiguran
87.0 p376, p405 Mutualists Fishing 40%
Coastal Kagayan
p405 Mutualists Fishing 15%
Isabela
42.0
North Luzon
37.9
Casiguran
87.0 p376 “The Agta (Casiguran) (group 12), a mutualist group
that exchanged labor and forest products with their neighbors in return for
agricultural products, making them analogous to the Mbuti and Birhor as far as
population density is concerned.” 1.0 LPACKINX Log10 of the Group 1 size (:18)
Packing index.
Using our structural endogamy (cohesion) method, we discover 40 “mutualist”
marriages, where all the brides marrying outside have parents that are members of
the Agta bicomponent, confirming Binford's description.
25
Dwight Read: I was looking at the preface of a book available online:
"This book aims to address these questions and provide some ideas on how
we may understand the principles that guide the development, stability and
growth of complex social systems. The question which will be returned to is:
what forces create and sustain an integrated whole? In other words, what
exactly is ‘cohesion’, and why should we be concerned with its scientific
investigation." The word cohesion caught my eye and I recall that this is
something you have been concerned with.
Right.
The book is "The Making of Society" 2011 by Robert G. Hercock. He goes on
to say: → "We are looking for deeper clues as to what makes society work, i.e.
what processes foster cooperation, altruism and harmony in society. Some of
the specific themes that will be addressed revolve around the impact of trust,
consultation and cooperation, in the building of cohesive communities and
organizations."
Right. That's what Tolga and I
have been looking at for clues about the evolution of human cooperation.
With the absence of dominance hierarchies based on gender, compared to
our closest relatives, humans evolved to recognize mating pairs within the
band or community, to recognize fathers and father’s kin as well as the kin of
mothers. This could form a basis for social cohesion among human foragers
that differs from other primates. One hypothesis is that to the extent that
differences in cohesion can be recognized and measured in forager societies,
the more cohesive subgroups will also exhibit greater cooperation within the
community.
But wait...