The rise and fall of cultures: modeling the evolution of cultural capacity, and the consequent collapse of populations

Hal Whitehead
Dalhousie University

Peter J. Richeron
UC Davis (Emeritis)

Patterns of environmental variation influence the utility, and thus evolution, of different learning strategies. We use stochastic,individual-based evolutionary models to assess the relative advantages of 15 different learning strategies (genetic determination,individual learning, vertical social learning, horizontal/oblique social learning, and contingent combinations of these) when competing in variable environments described by 1/f noise. When environmental variation has little effect on fitness, then genetic determinism persists. When environmental variation is large and equal over all time-scales ("white noise") then individual learning is adaptive. Social learning is advantageous in "red noise" environments when variation over long time-scales is large. Climatic variability increases with time-scale, so that short-lived organisms should be able to rely largely on genetic determination. Thermal climates usually are insufficiently red for social learning to be advantageous for species whose fitness is very determined by temperature. In contrast, population trajectories of many species, especially large mammals and aquatic carnivores, are sufficiently red to promote social learning in their predators. The ocean environment is generally redder than that on land. Thus, while individual learning should be adaptive for many longer-lived organisms, social learning will often be found in those dependent on the populations of other species, especially if they are marine. This provides a potential explanation for the evolution of a prevalence of social learning, and culture, in humans and cetaceans.

We used this individual-based model to show that, in environmental conditions dominated by red noise, extirpation may be an outcome of the evolution of cultural capacity. In red noise environments individual learning may be selected from the population. If the social learning system comes to lack sufficient individual learning or cognitively costly adaptive biases, behavior ceases tracking environmental variation. Then, when the environment does change, fitness declines and the population may collapse or even be extirpated. The modeled scenario broadly fits some human population collapses and might also explain nonhuman extirpations. Varying model parameters showed that the fixation of social learning is less likely when individual learning is less costly, when the environment is less red or more variable, with larger population sizes, and when learning is not conformist or is from parents rather than from the general population. Once social learning is fixed, extirpation is likely except when social learning is biased towards successful models. Thus, the risk of population collapse may be reduced by promoting individual learning and innovation over cultural conformity, or by preferential selection of relatively fit individuals as models for social learning.

Slides and References:

Download a PDF version of the slides for this talk.

Download Whitehead and Richerson, The evolution of conformist social learning can cause population collapse in realistically variable environments, Evolution and Human Behavior 30 (2009) 261-273.

About the speakers:

Hal Whitehead is a University Research Professor in the Department of Biology at Dalhousie University. He was educated at Cambridge University (BA Mathematics; Diploma in Mathematical Statistics; PhD Zoology). His research focuses on social organization and cultural transmission in the deep-water whales, but he also works on their their ecology, population biology and conservation. Field work is mainly carried out in the North Atlantic and South Pacific Oceans from a 12-m sailing boat. He has developed statistical tools and software for analyzing vertebrate social systems. He uses individual-based stochastic computer models to study cultural evolution, gene-culture coevolution and mating strategies. Hal coedited "Cetacean Societies: Field Studies of Whales and Dolphins" (University of Chicago Press; 2000) and has written "Sperm Whales; Social Evolution in the Ocean" (University of Chicago Press, 2003) and "Analyzing Animal Societies: Quantitative Methods for Vertebrate Social Analysis" (University of Chicago Press, 2008).

Peter J. Richerson Is Distinguished Professor Emeritus in the Department of Environmental Science and Policy at the University of California—Davis. His research focuses on the processes of cultural evolution. His 1985 book with Robert Boyd, Culture and the Evolutionary Process, applied the mathematical tools used by organic evolutionists to study a number of basic problems in human cultural evolution. His recent books with Boyd include Not By Genes Alone: How Culture Transformed Human Evolution, an introduction to cultural evolution aimed at a broad audience and The Origins and Evolution of Cultures, a compendium of their more important papers and book chapters. His recent publications used theoretical models to try to understand some of the main events in human evolution, such as the evolution of the advanced capacity for imitation (and hence cumulative cultural evolution) in humans, the origins of tribal and larger scale cooperation, and the origins of agriculture. He collaborates with Richard McElreath and Mark Lubell in an NSF funded research group devoted to the study of cultural transmission and cultural evolution in laboratory systems. He learned about red noise in a parallel career as an aquatic ecologist.

Contact Information:

Hal Whitehead
Department of Biology
Dalhousie University
Halifax, Nova Scotia, Canada
902-494-3723
902-494-3736
hwhitehe@dal.ca