However, within each of these periods of relative stasis, smaller punctuations have been detected between relatively short periods of stasis. In the prehistoric record of stone tools, for example, there are long periods of little change, interspersed with sudden dramatic cultural shifts, such as the Neolithic revolution or the transition between the Middle and Upper Paleolithic.
Importantly, upon close scrutiny, the punctuation in some cultural records exhibits an additional characteristic: within the long periods of seemingly little broad-scale cultural change, there are cultural shifts of a smaller scale. Reasons for the sudden changes in cultural repertoires continue to be debated, but this pattern of change has usually been attributed to external events, such as environmental changes or the evolution of new cognitive capacities. However, depending on the timescale studied and the time-resolution in which it is analyzed, changes in tool repertoire may appear punctuated and stepwise for example, in the prehistoric archaeological record, long periods of little change are separated by “cultural explosions,” brief periods of rapid cultural accumulation. The archaeological record indicates that cultural traits can accumulate exponentially over time and dramatic cultural losses can also occur. Our results suggest that the common attribution of sudden cultural shifts to external processes such as cognitive or environmental change may be unwarranted. This occurs, for example, through innovations that change the availability of food and lead to an increased population size or innovations that increase the effectiveness of cultural transmission. In our model, these changes of steady state occur when cultural processes can change the parameters of their own evolution. We suggest that the two types of punctuation may result from two processes: small punctuations are driven by innovations that trigger invention of related tools, and large punctuations reflect changes in the steady state of the size of the population’s tool repertoire.
Within these periods of relative stasis smaller punctuations occur, with sudden gain or loss of suites of tools.
The record shows long periods of little technological change, interspersed with abrupt increases in cultural complexity. We develop a computational model that incorporates characteristics of human innovation and offers an explanation for one of the puzzling observations in the archaeological record of stone tools: its extreme punctuation. Yet, understanding of the processes that drive cultural evolution is limited. The ability to accumulate culture is unique to hominids. Our model suggests that common interpretations of cultural shifts as evidence of biological change, for example the appearance of behaviorally modern humans, may be unwarranted. The smaller and more frequent punctuated cultural changes, on the other hand, are brought about by innovations that spur the invention of further, related, technology, and which occur regardless of whether the population is near its cultural steady state. These parameter-changing cultural innovations occur very rarely, but whenever one occurs, it triggers a dramatic shift towards a new cultural steady state. This steady state can be regarded as a cultural carrying capacity.
It also incorporates a realistic aspect of cultural evolution: cultural innovations, such as those that increase food availability or that affect cultural transmission, can change the parameters that affect cultural evolution, thereby altering the population’s cultural dynamics and steady state. Our model includes interdependent innovation processes that occur at different rates. Here we propose a dynamic model of cultural evolution that accommodates empirical observations: without invoking external factors, it gives rise to a pattern of rare, dramatic cultural bursts, interspersed by more frequent, smaller, punctuated cultural modifications. To explain these sharp cultural bursts, researchers invoke such external factors as sudden environmental change, rapid cognitive or morphological change in the hominids that created the tools, or replacement of one species or population by another. Punctuation on multiple timescales and magnitudes is also found in cultural trajectories from historical times. Within each such period, small punctuated cultural modifications take place. One of the most puzzling features of the prehistoric record of hominid stone tools is its apparent punctuation: it consists of abrupt bursts of dramatic change that separate long periods of largely unchanging technology.