Increasing population size can inhibit cumulative cultural evolution

Significance Cumulative cultural evolution (CCE)—the social-learning process through which adaptive modifications accumulate over historical time—is crucial to the advancement of the human species, and yet little is known about the factors important to CCE. Larger populations may enhance CCE, although this is contentious. We report a large-scale experiment that manipulates population size and tests its effect on artefact performance using a paper plane construction task. Over the experimental generations, smaller populations showed the strongest improvements in plane performance (indexed by flight distance). We conclude that larger populations do not enhance artefact performance via CCE and that it may be only under certain specific conditions that larger population sizes enhance CCE. The extent to which larger populations enhance cumulative cultural evolution (CCE) is contentious. We report a large-scale experiment (n = 543) that investigates the CCE of technology (paper planes and their flight distances) using a transmission-chain design. Population size was manipulated such that participants could learn from the paper planes constructed by one, two, or four models from the prior generation. These social-learning conditions were compared with an asocial individual-learning condition in which individual participants made repeated attempts at constructing a paper plane, without having access to any planes produced by other participants. Larger populations generated greater variation in plane performance and gave participants access to better-adapted planes, but this did not enhance CCE. In fact, there was an inverse relationship between population size and CCE: plane flight distance did not improve over the experimental generations in the 2-Model and 4-Model conditions, but did improve over generations in the 1-Model social-learning condition. The incremental improvement in plane flight distance in the 1-Model social-learning condition was comparable to that in the Individual Learning condition, highlighting the importance of trial-and-error learning to artifact innovation and adaptation. An exploratory analysis indicated that the greater variation participants had access to in the larger populations may have overwhelmed their working memory and weakened their ability to selectively copy the best-adapted plane(s). We conclude that larger populations do not enhance artifact performance via CCE, and that it may be only under certain specific conditions that larger population sizes enhance CCE.