NEOLITHIC FARMING IN EUROPE

Overview

The last glacial maximum, which occurred about 20,000 years ago, marked the height of the previous ice. Throughout this, and previous ice ages over some 2 million years, the early human population subsisted via hunting and gathering as best as local environmental conditions allowed with only rudimentary technology. The retreat of the ice sheets at about 10,000 years before present (BP), was accompanied by rapidly rising mean sea level and warmer wetter conditions at the mid-latitudes. This easing of climatic conditions not only allowed the re-occupation of more northerly regions abandoned to the advancing ice, but also saw the development of what is recognisable today as modern technology. From archeological evidence, this new farming technology is known to have originated in the middle east.

Remarkably, by 5,000 BP, a majority of the indigenous people in Europe were using the new farming technology, suggesting a rapid advance or adoption of the technology. In a seminal work, Ammerman and Cavalli-Sforza (1971) analysed this spread of farming technology in terms of a diffusive flow or displacement of population (which they termed a "demic" flow) which carried the new technology from the source region. Earlier work had considered diffusion as a mechanism, but only in terms of a `cultural' diffusion where technology was passed between indigenous peoples without significant actual movement of population. From the archaeological evidence, Ammerman and Cavalli-Sforza estimated the rate of advance of farming technology over the European mainland to be roughly 1 km per year.

Model

Single population

A simple computational model of the spread of a neolithic farming population has been developed by members of the NANIA group based on the work of Cohen (1992). The model solves the demic equation (essentially a diffusive spread of population plus a local logistic term representing population dynamics) on a realistic map of Europe. A given initial population grows and spreads in a way which can be made to reflect local conditions.

The figure on the left shows the time taken for a population in the model to expand from an initial source region in the middle east to occupy most of the European mainland (and north Africa). In this case the population takes 4000-5000 years to reach the westernmost regions (note there is no lnd correction between mainland Europe and the British Isles or northern Scandinavia in the model, so no population reaches these areas).

This model allows the saturation population to vary in space, here according to the local annual mean temperature. In the coldest regions, for example in the nest-east of the domain, no population can be supported. An arbitrarily complex environment model could be used, taking account of climate, land quality and so on.

More than one population

The model has been extended to include "technology diffusion" in addition to demic diffusion. This allows us to investigate scenarios where the movement of technology can outpace the movement of people. The model uses three separate populations - indigenous hunter-gatherers, neolithic farmers, and a "adopted farming" population of indigenous hunter-gatherers who have taken up the farming technology.

This figure shows the advance of a neolithic farming population (green) to regions occupied by indigenous hunter-gatherers (blue). At the point of contact, hunter-gatherers are able to "adopt" the farming technology and form a convert population (red). In this instance, the demic diffusion dominates over the technology diffusion and the convert population in overwhelmed by the advancing farmers.

This type of model allows the interplay of demic and technology diffusion to be investigated in addition to the affects of changes in local environment.

Code

The code used for the model is written in Java, and will be made available here soon, along with a preprint describing the work.

References


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