Biased dispersal can explain fast human range expansions

Joaquim Fort

doi:10.1038/s41598-020-66045-2

Abstract

Some human fronts spread faster than expected by models based on dispersal and reproduction. The only explanation proposed so far assumes that some autochthonous individuals are incorporated by the expanding populations, leading to faster front speeds. Here we show that simple models without this effect are also consistent with the observed speeds of two fronts (a Khoi-khoi expansion of herders and a Bantu expansion of farmers), provided that the dispersal of individuals is biased (i.e., more probable) in directions closer to the front propagation direction. The physical models presented may also be applied to other kinds of social phenomena, including innovation diffusion, rumor propagation, linguistic fronts, epidemic spread, diffusion in economic space and the evolution of cooperation in spatial systems. They can be also adapted to non-human systems with biased dispersal, including biological invasions, cancer tumors and virus treatment of tumors.

Highlights

Some human fronts spread faster than expected by models based on dispersal and reproduction
The populations involved in these two studies are the Khoi-khoi that spread from about 2,300 until 1,100 yr Before Present (BP) and replaced hunting-gathering by herding in southwestern Africa[18] and the Bantu farmers that spread southwards from the Great Lakes area from about 3,400 until 1,400 yr BP and replaced hunting-gathering by farming in southeastern Africa[19]
In this paper we have shown that when a population expands its range, the front speed can be substantially faster if the dispersal of individuals is biased towards the front propagation direction, which seems a very reasonable assumption because individuals will presumably tend to move towards places with more free space than to places with less free space

Summary

Introduction

Some human fronts spread faster than expected by models based on dispersal and reproduction. This seems reasonable because humans in a population invading a landscape will likely tend to migrate to places where the population density is still low, i.e., the probability of dispersal or migration will increase for directions closer to that of the front propagation (lower values of θ) and this should lead to faster fronts than isotropic (i.e., non-biased) dispersal.

Results

Conclusion