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.
Highlights
The process of human adaptation to novel environments is a uniquely complex interplay between cultural and genetic changes
While the field of cultural evolution has provided deep insights into the processes of cultural transmission[5,7], we still understand little about how cultural adaptation to novel environments might proceed, what if any, evidence of past selection might be found in cultural data, and how this might interact with genetic adaptation or interfere with genetic signatures of selective events
In analogy with the genetic case described above, does cultural adaptation generally occur from existing variation or from an innovation-limited process? It may be reasonable to assume that the process of cultural innovation proceeds more rapidly than genetic mutation but what does this mean for our understanding of adaptation and the signatures of adaptation? Understanding these dynamics demands close examination of the way in which we typically model innovation in cultural evolutionary systems
Summary
We assumed that the level of cultural adaptation to changed environmental conditions has no influence on the survival of the population or on population demography more generally, since, by definition, the population size is constant at N even after an environmental change. We assume that a cultural response to challenging environmental conditions may be more likely to prevent death rather than increase fertility (taking, again, the example of cold weather clothing above) To model this link between cultural adaptation and survival we relax the assumption of constant population size and define the following the birth-death process. The increase depends on the probability of spread of the cultural variant as well as the protection against death, quantified by q, that it confers compared to variant A This lends credence to the idea that the spread of a weakly beneficial cultural trait may facilitate true evolutionary rescue for human populations by prolonging the time a population can wait for a beneficial genetic mutation to arise and spread. Culture alone may be able to rescue a population, prevent or mitigate population bottlenecks, or extend the survival time of a declining population during which true evolutionary rescue may be possible in a way rare (or unique) for large, long-living organisms
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