The fundamentals of cultural adaptation: implications for human adaptation

Abstract

The process of human adaptation to novel environments is a uniquely complex interplay between cultural and genetic changes. However, mechanistically, we understand little about these processes. To begin to untangle these threads of human adaptation we use mathematical models to describe and investigate cultural selective sweeps. We show that cultural sweeps differ in important ways from the genetic equivalents. The models show that the dynamics of cultural selective sweeps and, consequently, their differences from genetic sweeps depend critically on cultural transmission mechanisms. Further, we consider the effect of processes unique to culture such as foresight and innovations in response to an environmental change on adaptation. Finally we show that a 'cultural evolutionary rescue', or the survival of an endangered population by means of cultural adaptation, is possible. We suggest that culture might make a true, genetic, evolutionary rescue plausible for human populations.

Figure 1

(A) The probability of a cultural selective sweep from standing variation generated by unbiased transmission (black solid line), conformity with $\theta =0.5$ (dashed-dotted line), anti-conformity with $\theta =-0.5$ (dashed line) or from de novo innovation (red line) after an environmental change.

Figure 2

Probability that variant a has frequency j shown on the x-axis at $T_0$ under (A) unbiased transmission, (B) conformity with $\theta =0.05$, and (C) anti-conformity with $\theta =-0.05$.

Figure 3

The difference in probability of a sweep from standing variation and a novel innovation with different strengths of ability for foresight (y axis) and directed innovation (x axis). We assume that foresight cannot perform better than directed innovation and so consider the bottom diagonal only.

Figure 4

An evolutionary rescue scenario where the ancestral variant causes excess mortality and the novel variant provides a survival benefit. $r=0.003,q=0.005,g=1,f=1,N_0=1000,i_0=1$.

Figure 5

(A) The mean time to evolutionary rescue and (B) the severity of the population bottleneck. $r=0.0004,g=1,N_0=1000,i_0=1$. Simulations ran until the population was extinct or exceeded its original size, indicating a cultural evolutionary rescue in this parameter range.

Figure 6

The time to population collapse, where cultural rescues do not occur, for different values of q. Threshold for extinction here is 5 individuals and is marked with a red solid line. Black and grey lines show total population sizes, red dashed lines show the frequency of the beneficial cultural trait. Higher frequencies of the beneficial trait delay population collapse—sometimes substantially. $r=0.05,f=2,g=1,N_0=1000$, initial frequency of derived cultural trait is 1/N, $i_0=1$.