The pace of cultural evolution

Abstract

Today, humans inhabit most of the world's terrestrial habitats. This observation has been explained by the fact that we possess a secondary inheritance mechanism, culture, in addition to a genetic system. Because it is assumed that cultural evolution occurs faster than biological evolution, humans can adapt to new ecosystems more rapidly than other animals. This assumption, however, has never been tested empirically. Here, I compare rates of change in human technologies to rates of change in animal morphologies. I find that rates of cultural evolution are inversely correlated with the time interval over which they are measured, which is similar to what is known for biological rates. This correlation explains why the pace of cultural evolution appears faster when measured over recent time periods, where time intervals are often shorter. Controlling for the correlation between rates and time intervals, I show that (1) cultural evolution is faster than biological evolution; (2) this effect holds true even when the generation time of species is controlled for; and (3) culture allows us to evolve over short time scales, which are normally accessible only to short-lived species, while at the same time allowing for us to enjoy the benefits of having a long life history.

Figure 1. Box-and-whisker plot of the distribution of the absolute values of rates on a natural log scale.

On a linear scale, the distribution of biological rates (n = 503) has a mean and standard deviation of 3,187±14,457d, respectively, and a range of 0.003–298,103.5d. The distribution of cultural rates (n = 573) has a mean of 4,709±27,069d and a range of 7–614,969d.

Figure 2. Biological rates and cultural rates plotted against the interval of time over which the rates are measured.

Biological rates (black circles) and cultural rates (gray squares) are inversely correlated to the interval of the time over which the rates are measured. The solid lines represent the linear mixed model of interaction that best fit the biological (black line) and cultural (gray line) distributions (Table 2).

Figure 3. Rates of cultural evolution are inversely correlated with their age.

The age of a rate corresponds to the midpoint, in years Before Present (BP), of the time interval over which the rate is calculated. The solid line represents the linear mixed model of interaction of rates with age (Table 3).

Figure 4. Biological rates and cultural rates calculated as change per generation.

Biological rates (black circles) and cultural rates (gray squares), calculated as change per generation, are inversely correlated to the interval of the time over which the rates are measured. The solid lines represent the linear mixed model of interaction that best fit the biological (black line) and cultural (gray line) distributions (Table 5). The conversion of rates from an absolute time scale to a generational time scale impacts mostly the biological rates from species with a short generation time. For any given amount of phenotypic change observed over any given time interval, the difference between rate of change per millions of years and rates of change per generation time increases as generation time of species increases. This effect explains why the difference between the slopes of the two linear models, although significant, is smaller (Table 5) than that shown in Figure 2.