Cultural population differences, cumulative culture, and the

Cultural population differences, cumulative culture, and the

Models of cultural differences
and cumulative culture
Marius Kempe1, Alex Mesoudi1, Stephen Lycett2
1Department
of Anthropology, Durham University
2School
of Anthropology & Conservation, University of Kent
[email protected]
Cultural differences
Cumulative culture
Differences between different populations’ cultures,
e.g. in songbirds & great apes.
Cultural traits that build on other cultural traits,
e.g. in technology, science, mathematics.
Example
Example
2
3
6
7
8
9 10
1
2
3
4
1
6
7
8
9 10
6
13 14 15
16 17 18
20
31
34 35
40
36 37
15
16 17 18 19 20
16 17 18
20
22 23 24
26 27 28 29 30
31 32
34 35
40
36 37 38
27 28
30
31
34 35
36 37
39 40
Population 2
Population 3
Population 4
Population 5
Population 6
2
6
7
3
4
5
1
9 10
6
4
19 20
16
21
36
13 14
16 17 18
23
7
34
34 35
40
70
60
Trait level:
50
Timestep: 0
40
14 15
18
16
20
23
28 29 30
26
(a)
10
11
20
Hough (1922)
4
23 24
26 27 28 29 30
31 32
1
6
13 14 15
Whiten et al (1999)
8
Population 1
1
5
13
22 23 24
28 29 30
7
4
13 14 15
23 24
26
3
Average level l
1
26 27 28 29 30
31 32
34 35
36 37
Model simulation (N = 100, a = 0.9, u = 0.1, m = 0)
➤
➤
1
2
0.2
Accuracy of social learning a
Migration rate m
0.3
0.2
0.1
20
30
40
50
60
70
Population size N
80
90
9
10
0.8
0.8
0.6
0.4
0.2
0.0
100
0.4
0.6
Accuracy
of social learning a
Results
Mean complexity level maintained
(c)
0.4
0.0
10
Model
3
4
5
6
7
8
(We extend a model by Enquist et al 2010.)
Number of cultural models n
5
Results
0.5
3000
The population contains N individuals.
(b)
➤ The 30
cultural trait comes in better and worse levels.
➤ Learning a level requires learning all previous levels.
25
➤ Each timestep, individual death and birth happens.
20
➤ Every newly born individual:
115
. picks n cultural models at random,
210
. learns each level they know with probability a, and
3. invents the next level with probability u.
➤
0
Mean similarity between populations
2500
Average level l
➤
2000
Model simulation (N = 100, n = 3, a = 0.85, u = 0.1)
20
(We extend a model by Strimling et al 2009.)
➤
1500
30
0
There are p populations containing N individuals.
Many equally useful cultural traits can be invented.
Traits are invented in a fixed sequence of ‘obviousness’.
Each timestep, individual death and birth happens.
Every newly born individual:
1. picks a cultural model at random,
2. learns each of its traits with probability a,
3. invents a new trait with probability u, and
4. migrates to another population with probability m.
1000
10
Model
➤
500
1
2
3
4
5
6
7
Number of cultural models n
8
9
10
Empirical values: 0.46 for chimpanzees (Whiten et al, 1999), 0.32 for orangutans (van Schaik et al, 2003).
Empirical values: 3-7 for marine foraging tools in Oceania (Kline & Boyd, 2010).
Populations can have cultural differences despite individuals
migrating between populations and inventing the same traits.
The complexity of cumulative culture depends on both social
learning accuracy and the number of cultural models.
Discussion
The two models can be combined into a single model which has two regimes, depending on whether an > 1 (Enquist et al 2010): one with many traits
and cumulative culture, and one with few traits and no cumulative culture. We suggest that these regimes correspond to human and nonhuman culture.
References
Enquist et al. 2010 One cultural parent makes no culture. Anim. Behav. 79; Hough 1922 Synoptic series of objects in the United States National Museum illustrating the history of inventions. Proc.
United States National Museum 60; Kline & Boyd 2010 Population size predicts technological complexity in Oceania. Proc. R. Soc. B 277; Strimling et al. 2009 Accumulation of independent cultural
traits. Theor. Pop. Biol. 76; van Schaik et al. 2003 Orangutan cultures and the evolution of material culture. Science 299; Whiten et al. 1999 Cultures in chimpanzees. Nature 399.