No subject

[CM ICTP - Trieste]

									07/04

JOINT ICTP/SISSA CONDENSED MATTER SEMINARS
Academic Year 2006/07



Seminar Room - Main Building
(first floor)


Wednesday, 20 June -     4:00 p.m.



Morrel H. COHEN
(Exxonmobil Research and Engineering Company, Annandale)



" Cultural hitchhiking on the wave of advance of beneficial 
technologies "


Abstract

The wave-of-advance model was introduced to describe the spread of 
advantageous genes in a population. It can be adapted to model the 
uptake of any advantageous technology through a population, such as the 
arrival of neolithic farmers in Europe, the domestication of the horse, 
the wheel, iron tools, political organisation or advanced weaponry. Any 
trait which preexists alongside the advantageous one could be carried 
along with it, such as genetics or language, regardless of any 
intrinsic superiority. Decoupling of the advantageous trait from other 
“hitchhiking” traits depends on its adoption by the preexisting 
population. I shall describe work done by Ackland, Signitzer, Stratford 
and myself in which we constructed a wave-of-advance model for 
agriculture based on food production on a heterogeneous landscape with 
interaction of multiple populations.  Two key results arise from 
geographic inhomogeneity: the “subsistence boundary” at land so poor 
that the wave of advance is halted, and the temporary “diffusion 
boundary” where the wave cannot move into poorer areas until its 
gradient becomes sufficiently large. At diffusion boundaries, farming 
technology may pass to indigenous people already in those poorer lands, 
allowing their population to grow and resist encroachment by farmers. 
Ultimately, this leads to the halt in spread of the “hitchhiking” trait 
and establishment of a permanent “cultural boundary” between distinct 
cultures with equivalent technology.  These phenomena are illustrated 
by simulations of the transition between hunting and gathering and 
neolithic agriculture in Europe and in the Indian subcontinent and by 
the advance of European agriculture into Southern Africa much later.  
Physical concepts underlie the construction of the model--diffusion, 
mobility, and an Einstein relation between them; nonlinear wave 
propagation in an inhomogeneous medium; relaxation processes.  The work 
provides an example of the power of physical reasoning in an 
interdisciplinary context.