Abstract
In the last few million years, the hominin brain more than tripled in size. Comparisons across evolutionary lineages suggest that this expansion may be part of a broader trend toward larger, more complex brains in many taxa. Efforts to understand the evolutionary forces driving brain expansion have focused on climatic, ecological, and social factors. Here, building on existing research on learning, we analytically and computationally model the predictions of two closely related hypotheses: The Cultural Brain Hypothesis and the Cumulative Cultural Brain Hypothesis. The Cultural Brain Hypothesis posits that brains have been selected for their ability to store and manage information, acquired through asocial or social learning. The model of the Cultural Brain Hypothesis reveals relationships between brain size, group size, innovation, social learning, mating structures, and the length of the juvenile period that are supported by the existing empirical literature. From this model, we derive a set of predictions—the Cumulative Cultural Brain Hypothesis—for the conditions that favor an autocatalytic take-off characteristic of human evolution. This narrow evolutionary pathway, created by cumulative cultural evolution, may help explain the rapid expansion of human brains and other aspects of our species’ life history and psychology.
Highlights
In the last few million years, the cranial capacity of the human lineage dramatically increased, more than tripling in size [1,2,3]
We develop an analytic model and agent-based simulation based on the Cultural Brain Hypothesis (CBH): the idea that brains have been selected for their ability to store and manage information via some combination of individual or social learning [16,17,18,19,20,21]
The analytical adaptive dynamics model we present in the Supplementary Materials allows us to understand the evolution of brain size, adaptive knowledge, and reliance on social learning as a function of transmission fidelity, asocial learning efficacy, and survival returns on adaptive knowledge without the complexities of co-evolutionary dynamics and explicit evolution of oblique learning and learning biases
Summary
Humans have extraordinarily large brains, which tripled in size in the last few million years. We present a theory, captured in an analytic and computational model, that explains these increases in brain size: The Cultural Brain Hypothesis. Cultural Brain Hypothesis learning by yourself), group size, mating structure, and the length of the juvenile period, which co-evolve with brain size The model captures this co-evolution under different conditions and describes the specific and narrow conditions that can lead to a take-off in brain size—a possible pathway that led to the extraordinary expansion in our own species. We call these conditions the Cumulative Cultural Brain Hypothesis. These theories are supported by our tests using existing empirical data
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