Slides from a talk presented at the 2014 London Evolutionary Research Network (LERN) conference. Abstract: An evolutionary interpretation of cooperative behaviours must ultimately include an increase the inclusive fitness of actors as well as recipients. At the proximate level, mechanisms for encouraging and maintaining cooperation include factors such as kin discrimination, limited dispersal as well as direct and indirect reciprocity. However humans are also known for co-operating with individuals who are not necessarily close relatives, and often in co-operative groups. Here, we aim to quantify the relative importance of kinship and social group membership as mediators of cooperative behaviour. Using a modified, externally valid Dictator Game, we test whether indigenous Saami reindeer herders in Norway preferentially give gifts to genetic relatives or to members of their cooperative herding group (the ‘siida’). Membership of the same siida strongly increased the odds of receiving a gift. Kinship had a small (and not statistically significant) effect, even for close relatives. Gifts were not preferentially given to younger family members. These patterns suggest that social grouping can trump genetic factors in mediating cooperative behaviour in this population. This is likely due to the importance of herding groups in day-to-day subsistence.

1. Gift games among Saami pastoralists show
group membership can be more important
than genetic kinship
Matthew G. Thomas
Bård-Jørgen Bårdsen
Marius Warg Næss
Ruth Mace

2. Who do herders help?
Cooperative herding
- sharing, defending, loaning, exchanging
- lowest cost strategy
- pooling risk
- presence of relatives associated with increased herd size
Cooperation influenced by mix of genetic (kin selection)
and social factors (reciprocity)
Aktipis et al. 2011; Apicella et al. 2012; Gerkey 2013; Lamba & Mace 2011; Næss et al. 2010

3. What makes people more likely to receive gifts?
Hypotheses:
Genetic kinship > cultural kinship
 gifts to relatives
Cultural kinship > genetic kinship
 gifts to cooperative group
Wealth flows: gifts given to younger family members
Kaplan 1994; Hamilton 1964; Trivers 1971

4. Study site: Finnmark, Norway
~3,500 Saami reindeer herders
533 license owners
(75 in study district)

5. Saami reindeer husbandry

6. Households form cooperative
groups: the siida
Summer siidas contain
from 10 to 100+ people
Summer siidas split into
smaller, family-oriented
winter siidas
70°
65°
60°
10° 20°
From Næss (2009)
100 km

7. Methods
Interviewed 30 (out of 75) licensed herd owners in a district
Externally valid, culturally salient experimental game:
anonymous gifts of petrol
Assembled complete kinship network for district

8. Results

9. Gift network
Colours are siidas
Circles = 75 license owners
(Size is no. gifts received)

10. Gift network
Colours are siidas
Circles = 75 license owners
(Size is no. gifts received)
Filled circle = 30 interviewees

11. Gift network: 71 gifts given. 45 given within siida.
Colours are siidas
Circles = 75 license owners
(Size is no. gifts received)
Filled circle = 30 interviewees
Lines = gifts
(Thickness is gift size)

12. Breakdown of gifts:
Same siida? Related?
Gift?
Yes
Yes
Yes 30
No 15
No
Yes 3
No 23

13. Breakdown of gifts:
Highest proportion given to kin in same siida
Same siida? Related?
Gift?
Yes No
Yes
Yes 30 74
No 15 153
No
Yes 3 88
No 23 1,834
Total of 2,220 potential gifts
given from 30 interviewees
to any of 75 people
Yes
No
Yes
No
Yes
No
Yes
No

14. Most of the 23 gifts to non-kin in other siidas are for ‘good’ or new herders
Good herders: 8
Young/new owners: 5
Lazy: 3
Old friend: 1
Current or future reciprocity:
2
Need help: 1
Family: 2
(No reason given): 1

15. Siida membership is strongest predictor of receiving a gift
Model Predictors Odds ratio p value ΔAIC
(the best model)
Close family only
Member of same summer siida? (ref: no) 24.29 0.004
0.000
Close family ( )? (ref: no) 6.05 0.24
All relatives
Member of same summer siida? (ref: no) 19.11 <0.001
1.006
Genetic relative ( )? (ref: no) 4.66 0.068

16. Gifts not preferentially given to younger family
Gifts to kin Gifts to non-kin
to younger
herders
to older
herders
to younger
herders
to older
herders

17. Siida membership makes people more likely to receive gifts
Hypotheses:
Genetic kinship > cultural kinship
 gifts to relatives
Cultural kinship > genetic kinship
 gifts to cooperative group
Wealth flows: gifts not given to younger family members

18. Summary
Belonging to the same siida is strongest predictor of receiving gifts
But gifts given to non-kin in other siidas
- reputation and reciprocity
No age bias in gift giving
Studies of cooperation to understand high reindeer death rate

19. Thanks
Ruth Mace
Andrea Migliano
Human Evolution Ecology Group at UCL
Katharina Olsen
Jon Mikkel Eira
The herders of Finnmark
ERC
Framsenteret
Norsk Institutt for Naturforskning
CICERO

20. References
Aktipis, C. A., Cronk, L., & Aguiar, R. (2011). Risk-Pooling and Herd Survival: An Agent-Based Model of a Maasai Gift-Giving
System. Human Ecology, 39, 131–140
Apicella, C. L., Marlowe, F. W., Fowler, J. H., & Christakis, N. A. (2012). Social networks and cooperation in hunter-gatherers.
Nature, 481, 497–501
Gerkey, D. (2013). Cooperation in context: Public goods games and post-Soviet collectives in Kamchatka, Russia. Current
Anthropology, 54, 144–176
Lamba, S., & Mace, R. (2011). Demography and ecology drive variation in cooperation across human populations.
Proceedings of the National Academy of Sciences of the United States of America, 108, 14426–30
Næss, M. W., Bårdsen, B.-J., Fauchald, P., & Tveraa, T. (2010). Cooperative pastoral production — the importance of kinship.
Evolution and Human Behavior, 31, 246–258
Ohtsuki, H., Hauert, C., Lieberman, E., & Nowak, M. A. (2006). A simple rule for the evolution of cooperation on graphs and
social networks. Nature, 441, 502–5
Trivers, R. (1971). The evolution of reciprocal altruism. Quarterly Review of Biology, 46, 35–57
West, S. A., Griffin, A. S., & Gardner, A. (2007). Evolutionary explanations for cooperation. Current Biology, 17, R661–72