Original Articles
Experimental models for testing hypotheses about cumulative cultural evolution

https://doi.org/10.1016/j.evolhumbehav.2007.12.001Get rights and content

Abstract

The rapid appearance (over evolutionary time) of the cognitive skills and complex inventions of modern humans has been attributed to “cumulative cultural evolution” (CCE), the accumulation of knowledge and skills over generations. To date, researchers have only been able to speculate about the reasons for the apparent absence of this phenomenon in nonhumans, and it has not been possible to test hypotheses regarding the mechanisms underlying it. Here, we show that it is possible to demonstrate CCE under laboratory conditions by simulating generational succession through the repeated removal and replacement of human participants within experimental groups. We created “microsocieties” in which participants were instructed to complete simple tasks using everyday materials. In one of our procedures, participants were instructed to build a paper aeroplane which flew as far as possible, and in the other, they were instructed to construct a tower of spaghetti which was as tall as possible. We show that, in both cases, information accumulates within the groups such that later generations produce designs which are more successful than earlier ones. These methods offer researchers a window to understanding CCE, allowing for experimental manipulation and hypothesis testing.

Introduction

The rapid appearance (over evolutionary time) of the cognitive skills and complex inventions of modern humans has been attributed to “cumulative cultural evolution” (CCE) (Boyd and Richerson, 1996, Richerson and Boyd, 2005, Tomasello, 1999). The term CCE is used to describe the way that knowledge accumulates in human populations over time, such that each generation makes use of behaviours and artefacts invented by previous generations, which they would be unlikely to have been able to invent by themselves (Boyd and Richerson, 1996, Richerson and Boyd, 2005, Tomasello, 1999). It has been argued that, although social learning is relatively common in the animal kingdom, CCE is extremely rare, possibly restricted to humans (Boyd and Richerson, 1996, Galef, 1992, Tomasello, 1999). It has also been suggested that CCE may even be dependent on learning mechanisms which are unique to humans and is consequently not possible in nonhumans (Tomasello, 1999), although this remains contentious (e.g., see Whiten, Horner, & Marshall-Pescini, 2003). Understanding CCE may therefore represent an important element in understanding human nature, particularly as it has allowed humans to develop powerful technologies, assemble complex societies, use symbolic forms of communication, and exploit an unusually wide range of habitats (Boyd & Richerson, 1996). However, to date, research on CCE has been restricted to historical approaches, such as those which classify and sequence human artefacts (Basalla, 1989, O'Brien et al., 2001), and comparative approaches, which draw comparisons between human behaviour and that of other animals, such as chimpanzees (Boesch, 2003, Tomasello et al., 1993, Tomasello et al., 1993, Whiten et al., 2003). Therefore, researchers have only been able to speculate about the reasons for its apparent absence (or at least its relative rarity, e.g., see Boesch, 2003) in other species and the abilities upon which it depends in humans.

This has led to considerable debate (Whiten, 2005) and little consensus. For example, Boyd and Richerson (1996) and Tomasello (Tomasello, 1999, Tomasello et al., 1993, Tomasello et al., 1993) have suggested that CCE may depend on specific social learning mechanisms, in particular, imitation and/or teaching. Since imitation and teaching have traditionally proven notoriously difficult to identify in animals (Caldwell and Whiten, 2002, Caro and Hauser, 1992), their arguments have provided a conveniently neat explanation for the apparent absence of CCE. However, this has not gone undisputed (Heyes, 1993, Laland and Hoppitt, 2003). Laland (2004) has suggested that CCE may instead depend on an ability to appraise the relative effectiveness of behavioural alternatives and that this could be beyond the capabilities of nonhumans. In contrast, Whiten, 2005, Whiten et al., 2003) has proposed that the crucial factor may be the unusual complexity of human behaviours and that this accounts for CCE rather than particular social learning mechanisms.

Our aim was to demonstrate that CCE could be studied under laboratory conditions. Such a demonstration would allow this debate to move from theoretical speculation into the realms of empirical testability. We therefore wanted to show that improvement in performance on a task could be passed on within groups over miniaturised “generations” of learners. We used a microsociety design, in which generational succession is simulated through the repeated removal and replacement of participants within groups (e.g., Baum et al., 2004, Jacobs and Campbell, 1961). This method also has similarities with the transmission chain method, originally pioneered by Bartlett (1932) and more recently applied by Mesoudi (e.g., Mesoudi, 2007, Mesoudi and Whiten, 2004, Mesoudi et al., 2006). We presented groups of participants with challenges involving the construction of simple artefacts. In one of our tasks, groups of participants were asked to build a paper aeroplane from a sheet of paper that would fly as far as possible. In the other task, 10 groups of participants were asked to construct a tower from spaghetti and modelling clay, which was as high as possible. It was predicted that the performance of these chains of individuals would improve over successive generations. It was also predicted that the artefacts produced by participants would themselves show physical evidence of social learning in that structures would be more similar within chains than across them.

Section snippets

Participants

Participants were recruited on campus at the University of Stirling and from two local secondary schools. For the paper planes study, 10 chains of 10 participants took part. Their mean age was 20 years (S.D., 6.02, youngest=13, eldest=48), and the ratio of males to females was approximately 50:50 (53 males, 47 females). Ten chains of 10 participants also took part in the spaghetti towers study. Their mean age was 21 years (S.D., 7.14, youngest=11, eldest=47), and the ratio of males to females

Results

Consistent with the idea that information accumulated within the groups, later artefacts were more successful in terms of the goal measures (of distance flown and height) than earlier ones. The planes produced by the first participants in each group flew a mean best distance of 226.5 cm (S.D., 104.1), and those produced by the tenth participants flew a mean best distance of 714.6 cm (S.D., 334.9). A related t test confirmed a significant difference between the first and 10th planes (t9=4.706, p

Discussion

We conclude that our results show that it is possible to demonstrate CCE under controlled laboratory conditions. We found improvement in performance over generations of learners within the group, consistent with the accumulation of knowledge and skills (or a “ratchet effect,” Tomasello, 1999). We also found evidence of descent with modification within the chains, as we found clear evidence that designs were more similar within chains than across them and, also, that designs that were closer

Acknowledgments

We thank C. Hill and J. Davies for help with data collection and pilot work. We are very grateful for the cooperation of staff at Lornshill High School and Grangemouth High School.

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    This work was supported by a grant from the Economic and Social Research Council (ESRC) to C.A.C. (RES-061-23-0072).

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