Geoscience Reference
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Europe around 45-40 ka ago, where they were associated with the development of
very distinctive Upper Palaeolithic industries (the Dabban in North Africa and the
Aurignacian in Europe) (Olivieri et al.,
2006
). These conclusions seem secure, but
it should always be borne in mind that errors can occur as a result of the 'founder
effect', which involves the loss of genetic variation that arises when a relatively small
number of individuals establish a new population. Refined
14
C-dating shows that
anatomically modern humans had reached southern Italy by 45-43 ka (Benazzi et al.,
2011
) and south-west England by 41-39 ka (Higham et al.,
2011
), bringing new stone
tool-making methods with them.
The Last Glacial Maximum (LGM: around 21 ka ago) was a time of extreme
global environmental stress. The Y chromosome genetic evidence suggests that dur-
ing the extreme environment of the LGM, there was a drop in population numbers
and people sought refuge in isolated areas (Underhill et al.,
2001
), from which refugia
they branched out as the ice caps and glaciers retreated, temperatures became warmer
and conditions improved for
H. sapiens
but not necessarily for the Neanderthals. The
evidence from securely dated river and lake deposits, dunes, dust mantles, periglacial
and glacial features, plant and animal fossils, marine cores and oxygen isotope studies
(all reviewed in earlier chapters), taken together, points to colder global temperatures
and greater-than-present aridity between latitudes 30
S during and imme-
diately after the LGM. Peak aridity appears to have coincided with early postglacial
warming and the release of abundant meltwater into the North Atlantic, which led
to a weakening of the oceanic thermohaline circulation system. Precipitation min-
ima and evaporation maxima may have been slightly out of phase with maximum
wind intensities, so the dune and dust records need to be interpreted with care. This
late Pleistocene phase of aridity was broadly synchronous in both hemispheres and
marked the greatest expansion of our deserts since the advent of
Homo sapiens
(and
the associated Middle Stone Age cultures) some 200 ka ago. Earlier intervals of major
Pleistocene aridity also coincided with global temperature minima. Glacial maxima
were times of low atmospheric carbon dioxide content, low atmospheric water vapour
content, high ultraviolet radiation, greater windiness, lower temperatures, lower pre-
cipitation and increased evapotranspiration, which means that physiological stress to
plants and dependent animals would have been great. Given these extreme conditions,
it seems probable that prehistoric hominids occupied the great tropical deserts, such as
the Sahara and Arabia, during milder climatic intervals, especially the relatively short-
lived interglacial phases, when water, plants and animals were more easily available,
rather than during the glacial maxima (Williams et al.,
1987
; Osborne et al.,
2008
;
Castaneda et al.,
2009
; Drake et al.,
2011
).
Scattered throughout the Sahara are abundant remains of the stone tools left behind
by the Early, Middle and Late Stone Age peoples who once roamed the Sahara during
these wetter climatic intervals (Clark,
1980
, Gifford-Gonzalez,
2008
).TheLateStone
Age hunters who preyed on the savanna herbivores were also gifted artists, leaving
°
N and 30
°
