[ExI] High population density triggers cultural explosions

Emlyn emlynoregan at gmail.com
Fri Jun 5 06:44:30 UTC 2009

This makes all kinds of sense to me.

High population density triggers cultural explosions

Increasing population density, rather than boosts in human brain
power, appears to have catalysed the emergence of modern human
behaviour, according to a new study by UCL (University College London)
scientists published in the journal Science. High population density
leads to greater exchange of ideas and skills and prevents the loss of
new innovations. It is this skill maintenance, combined with a greater
probability of useful innovations, that led to modern human behaviour
appearing at different times in different parts of the world.

In the study, the UCL team found that complex skills learnt across
generations can only be maintained when there is a critical level of
interaction between people. Using computer simulations of social
learning, they showed that high and low-skilled groups could coexist
over long periods of time and that the degree of skill they maintained
depended on local population density or the degree of migration
between them. Using genetic estimates of population size in the past,
the team went on to show that density was similar in sub-Saharan
Africa, Europe and the Middle-East when modern behaviour first
appeared in each of these regions. The paper also points to evidence
that population density would have dropped for climatic reasons at the
time when modern human behaviour temporarily disappeared in
sub-Saharan Africa.

Adam Powell, AHRC Centre for the Evolution of Cultural Diversity,
says: "Our paper proposes a new model for why modern human behaviour
started at different times in different regions of the world, why it
disappeared in some places before coming back, and why in all cases it
occurred more than 100,000 years after modern humans first appeared.

"By modern human behaviour, we mean a radical jump in technological
and cultural complexity, which makes our species unique. This includes
symbolic behavior, such as abstract and realistic art, and body
decoration using threaded shell beads, ochre or tattoo kits; musical
instruments; bone, antler and ivory artefacts; stone blades; and more
sophisticated hunting and trapping technology, like bows, boomerangs
and nets.

Professor Stephen Shennan, UCL Institute of Archaeology, says: "Modern
humans have been around for at least 160,000 to 200,000 years but
there is no archaeological evidence of any technology beyond basic
stone tools until around 90,000 years ago. In Europe and western Asia
this advanced technology and behaviour explodes around 45,000 years
ago when humans arrive there, but doesn't appear in eastern and
southern Asia and Australia until much later, despite a human
presence. In sub-Saharan Africa the situation is more complex. Many of
the features of modern human behaviour - including the first abstract
art - are found some 90,000 years ago but then seem to disappear
around 65,000 years ago, before re-emerging some 40,000 years ago.

"Scientists have offered many suggestions as to why these cultural
explosions occurred where and when they did, including new mutations
leading to better brains, advances in language, and expansions into
new environments that required new technologies to survive. The
problem is that none of these explanations can fully account for the
appearance of modern human behaviour at different times in different
places, or its temporary disappearance in sub-Saharan Africa."

Dr Mark Thomas, UCL Genetics, Evolution and Environment, says: "When
we think of how we came to be the sophisticated creatures we are, we
often imagine some sudden critical change, a bit like when the black
monolith appears in the film 2001: A Space Odyssey. In reality, there
is no evidence of a big change in our biological makeup when we
started behaving in an intelligent way. Our model can explain this
even if our mental capacities are the same today as they were when we
first originated as a species some 200,000 years ago.

"Ironically, our finding that successful innovation depends less on
how smart you are than how connected you are seems as relevant today
as it was 90,000 years ago."


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