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200“100 kyr

This interval coincides with OIS 7“5 that lasted for 64 kyr. This was a cold
period, the ¬rst part weakly stable and the latter unstable allowing for brief
milder intervening periods. The preceding long interval of warmth of 250 kyr
that may have included a new African colonisation and the arrival of Mode 3
technology seems to have permitted the persistence through the short 36-kyr
64 Neanderthals and Modern Humans

interval that included the ¬rst part of OIS 6. The warm but short OIS 5
may have allowed a brief recovery of a population that is then identi¬able as
Neanderthal.


50“0 kyr

This interval coincides with OIS 2 that lasted 11 kyr. This was a cold and
unstable period that saw the extinction of the Neanderthals, whose population
had already been critically stressed in the preceding periods, and the severe
population fragmentation and subsequent recovery in OIS 1 of Modern Humans
(Demars, 1996; Torroni, et al., 1998; Bocquet-Appel & Demars, 2000a).
These results indicate that there have been ¬ve major episodes that affected
Europe:

(1) The colonisation by H. antecessor or its ancestor with Mode 1 before
780 kyr which was restricted to the south. This population probably went
extinct in either OIS 20, 18 or 16.
(2) The colonisation by H. heidelbergensis with Mode 2 during OIS 15 be-
tween 600 and 550 kyr. This population survived for up to 400 kyr and
the Neanderthals probably evolved directly from them.
(3) A colonisation during OIS 7 between 250 and 200 kyr. This may have been
in the form of hominids (H. helmei) carrying Mode 3, in which case their
relationship with European H. heidelbergensis would be of great interest,
or it may have been a technological diffusion from Africa at a time when
the European and African populations were not isolated.
(4) The Neanderthal extinction during OIS 3 between 40 and 30 kyr.
(5) The survival and expansion of H. sapiens after 40 kyr.



Contact between African and European populations

There is therefore the distinct possibility that African and European populations
met, at least, on two or three occasions with its clear implications for gene ¬‚ow.
The ¬rst would have been when H. antecessor or its ancestor colonised southern
Europe and met earlier populations that may have arrived before 1 Myr. Al-
ternatively, H. antecessor may have evolved from these populations in Europe.
Further evidence of the pre-800 kyr colonisation of Europe is required. The
second was the interchange between 250 and 200 kyr when Mode 3 was intro-
duced into Europe. The question of whether the Neanderthals evolved from local
H. heidelbergensis, from an African newcomer (H. helmei) or derived genes
Human range expansions, contractions and extinctions 65

from the two populations is of great interest. Thirdly, there is the best-
documented case of the arrival of Modern Humans around 40 kyr (Hammer,
et al., 1997; Malaspina et al., 1998; Semino et al., 2000; Shen et al., 2000; Bar-
bujani & Bertorelle, 2001; Reich et al., 2001; Marth et al., 2003) and their rela-
tionship to the Neanderthals that will occupy most of the discussion of this book.


Persistence of hominid populations

Foley (1994) showed that hominid extinction in the last 5 Myr was corre-
lated with low temperature. The results presented here indicate an increasing
capacity for persistence in Europe within the last 800 kyr. Homo antecessor
was restricted to the south and probably went extinct. Homo heidelbergensis
reached mild oceanic north-west Europe and persisted signi¬cantly longer. The
Neanderthals colonised areas further east than H.heidelbergensis and persisted
through conditions that were colder and more unstable than those experienced
by H. heidelbergensis. Finally, Modern Humans arrived in conditions that would
not have previously led to European colonisation. Their survival of OIS 2 was,
however, not exceptional.


Geographical origin of early European Modern Humans

The entry of Moderns into Europe during the Upper Palaeolithic may have been
in the form of a series of waves (Richards et al., 2000; Semino et al., 2000).
The evidence that Moderns with Aurignacian technology (the earliest Mode 4;
Klein, 1999) came from Africa is unconvincing (Sokal et al., 1997; Richards
et al., 1998; Bar-Yosef, 2000). Otte (1994) has proposed that the Modern
Aurignacian colonisation of the European Plains came from the eastern plains
of Eurasia and recent genetic evidence supports this view (Semino et al., 2000;
Bosch et al., 2001; Wells et al., 2001). The early Palaeolithic expansion into
northwest Siberia, prior to the split into western and eastern groups (Derbeneva
et al., 2002), would be consistent with a west-central Asian origin as would
the very early appearance of humans in the European Russian Arctic at 40
kyr (Pavlov et al., 2001) and in north-east Asia at 42 kyr (Brantingham et al.,
2001). In this scenario, the Aurignacians would have been people that colonized
Eurasia during an earlier colonization event and developed the Aurignacian out-
side Africa. These populations may have been related to those that appeared
in the Middle East around 100 kyr (Chapter 4) or they may have been part of
the Mode 3 colonisation at 250“200 kyr or of a more diffuse dispersal from the
Middle East to proximal regions between 450 and 200 kyr. Those populations
66 Neanderthals and Modern Humans

colonising Europe would have interacted with H. heidelbergensis leading to
the Neanderthals and those reaching H. heidelbergensis-free central Asian ar-
eas would have continued a separate evolution with close af¬nities with the
Zagros Mountains to the south (Davis & Ranov, 1999) and colonising ecotonal
zones in southern Siberia, to the north-east, by 130 kyr (Goebel, 1999). Thus the
Neanderthals and the Moderns would share a recent common ancestor, as pro-
posed by Foley & Lahr (1997), but the Neanderthal difference would have come
from adaptation to local conditions (Finlayson et al., 2000a) and/or hybridis-
ation between H. heidelbergensis and the form named H. helmei by Foley &
Lahr (1997). These populations would have only been isolated from each other
for a maximum of 350 kyr.


The Mediterranean and hominids in the Pleistocene

The Mediterranean lies in an intermediate latitude between the African tropics
and Europe. In the west, the Strait of Gibraltar is generally assumed to have been
a barrier to human dispersal (Straus, 2001). In the east, the Levant is generally
regarded a corridor and a point of contact (Tchernov, 1992, 1998).


The Middle East

The proximity of the Levant to East Africa and its relatively low latitude means
that a greater number of human dispersals from Africa would be expected to
reach that zone than Europe itself. If we work on the premise that unstable
intervals (that would have included warm periods within), in addition to the
warm stable ones that allowed colonisation of Europe, could have opened a
window for humans to reach the Middle East then we predict that humans could
have reached the region on at least six occasions. These would be: (a) 850“800
kyr; (b) 700“650 kyr; (c) 600“500 kyr; (d) 450“200 kyr; (e) 150“100 kyr; and
(f) 50“0 kyr. Of particular interest is the extended period of 250 kyr between 450
and 200 kyr that could have permitted a number of dispersals of which only that
with Mode 3 technology between 250 and 200 kyr reached Europe. The Middle
East could have acted as a secondary source for populations to temporarily
colonise adjacent geographical areas without penetrating into Europe. From
here populations could have dispersed eastwards keeping to similar latitudes.
Central Asian areas would also have been close and the presence of H. ergaster
in Dmanisi (Gabunia et al., 2000) indicates that penetration through the valleys
of the Caucasus was possible from an early date. The other interesting period
is 150“100 kyr that coincides with the presence of Moderns in the Levant that
Human range expansions, contractions and extinctions 67

does not appear to have materialised into a European colonisation (Bar-Yosef,
1998). The subsequent presence of Neanderthals in these sites would coincide
with the cold and stable conditions between 100 and 50 kyr that would have,
according to the data presented here, caused a contraction of the Modern range.
Finally, the 50“0 kyr period would have been favourable for a Middle Eastern
colonisation.


The Maghreb

The Maghreb is in a similar situation to the Levant and similar periods of
colonisation could have brought humans to this region. The barrier would have
been the Sahara during cold and arid events (deMenocal, 1995). It follows that
gene ¬‚ow between Maghreb and tropical African populations would have been
more frequent than between tropical African and European populations and,
as with the Levant, there would have been a relatively continuous trickle of
populations except in the coldest and most arid moments, i.e. 750“700 kyr,
650“600 kyr, 500“450 kyr, 200“150 kyr and 100“50 kyr coinciding with OIS
20, 18, 16, 12, 6 and 4.


The Iberian Peninsula

If the Strait of Gibraltar was a barrier for humans from 850“0 kyr then the Iberian
Peninsula would always have been reached by colonisers that ¬rst reached cen-
tral Europe. In that scenario, Iberia would be a part of the process of European
colonisation and a refugium for stressed populations during cold events. The
Strait of Gibraltar existed throughout this period although there were times
when its width was considerably narrower than the present-day 14 km (Alimen
1975; Giles Pacheco & Santiago P©rez, 1987). Conditions of almost neutral cur-
rent that ¬‚ow between the Atlantic and the Mediterranean would have existed
between glacials and interglacials (Fa et al., 2001). The possibility that humans
got across the Strait during this long period is likely. Populations able to cross
would meet similar bioclimates and could colonise much of Iberia without ¬rst
having to adapt to central European conditions. If we assume that the most
favourable moments would have been between warm and cold events, as pop-
ulations became compacted through habitat shrinkage and current ¬‚ows were
favourable, then the following periods would be predicted as likely: around 750
kyr, 650 kyr, 500 kyr and 200 kyr. To this we may add another moment prior to
the time scale under investigation that would have permitted an entry of humans
that were the precursors of H. antecessor (? H. ergaster). The third event would
68 Neanderthals and Modern Humans

account for the similarity in Acheulian artefacts on both shores of the Strait
of Gibraltar (Alimen, 1975; Giles & Santiago P©rez, 1987) and the fourth for
the presence of Mousterian in Iberia and the Maghreb (Allsworth-Jones, 1993).
The absence of potential crossings after this would explain why the Aterian
never reached Iberia (Deb©nath, 2000; Straus, 2001, but see Bouzouggar et al.,
2002).



Italy and the Balkans

Crossings from Africa into Italy would have been less likely (Alimen, 1975).
The Italian (Mussi, 1999) and Balkan (Bar-Yosef, 2000) peninsulas may have
acted as short-term refugia during glaciations but their smaller area relative to
Iberia and their more continental disposition would have rendered them less
effective.


The role of the mid-latitude belt

The mid-latitude belt that, as we saw in Chapter 2, stretches from Portugal and
Morocco in the west to the Himalayas in the east (Figure 2.1), has not previ-
ously been considered a unit in biogeographical terms. Yet, in terms of faunal
composition, topography and vegetation structure (Chapter 2) it stands as a sin-
gle unit, especially in the centre and west. In addition, the northern areas (not
dissected from the north by the Mediterranean) were the most important glacial
refugia (Chapter 7). In my view understanding this mid-latitude belt as a unit
is crucial in understanding human evolution in Eurasia and North Africa. The
colonisation of this belt by an early population that diverged from the African
hominids around 500 kyr (Chapter 5) is central to our understanding of the
Neanderthals and other archaic hominids. These robust archaic hominids, often
referred to as heidelbergensis, would have been well-adapted to the topogra-
phy and fauna of this belt. Westwards and eastwards dispersal, probably from
an origin close to the entry point from Africa that is most likely to have been
in the Middle East, and further adaptation to the conditions of this wide area
led to the evolution of the Neanderthals. Isolation in glacial refugia may have
differentiated Iberian, Balkan and Caucasus populations but gene ¬‚ow during
milder intervals would have maintained cohesion which allows us to lump them
all as Neanderthals. I predict that, as more data become available, differences
between Iberian, Balkan, Caucasus and other Neanderthal populations will be-
come apparent. There would have been a parallel spread along the southern
shores of the Mediterranean to north-west Africa but these populations would
Human range expansions, contractions and extinctions 69

have remained isolated from the Neanderthals by the Mediterranean and also
by the periodic expansions of the Sahara. This would explain the similarities
and differences between the Jebel Irhoud humans and the Neanderthals (Hublin,
1992; Allsworth-Jones, 1993), but see Simmons & Smith (1991) and Smith et al.
(1995) for an alternative perspective that requires contact across the Strait of
Gibraltar. A similar separation of eastward-expanding populations along the
southern mid-latitude belt would not have produced similar differentiation as
there would have been no physical barrier comparable to the Mediterranean or
the Sahara. As we have seen, the North African and Middle Eastern popula-
tions would have been subsequently more in¬‚uenced than the Neanderthals by
African gene ¬‚ow. The situation may have been similar in the Upper Palaeolithic
even though the expanding populations in Europe were arriving across the plains
and not the mid-latitude belt itself. The Modern North African Berber mtDNA
lineage appears to have diverged from the most ancient European and Middle
Eastern lineage around 50 kyr, one-third of their genes having a Middle Eastern
ancestry and one-eighth being sub-Saharan (Macaulay et al., 1999). North-west
African populations had a 75% Y chromosome contribution to the gene pool
from East Africa contrasting with a 78% contribution to the Iberian population
from western Asia along the northern rim of the Mediterranean with the Strait of
Gibraltar acting as a strong, but incomplete, barrier (Bosch et al., 2001). These
results further emphasise the western/central Asian genetic input to western
populations of Moderns, being more pronounced in Europeans than in North
Africans that continued to receive a proportional contribution from Africa.



Synthesis

In Chapter 2, I identi¬ed four main elements that contributed to human evo-
lution and expansion: (1) medium-sized mammalian herbivore availability; (2)
terrain topography; (3) habitat and landscape structure and distribution; and (4)
physical and ecological barriers. From this chapter we can add the following
re¬nements:


(1) As increasing climate variability created increasing spatial heterogene-
ity of habitats and landscapes in Africa, hominids became increasingly
dependent on intermediate and open habitats and landscapes, evolving
adaptations that permitted them to deal with the spatial uncertainties char-
acteristic of such environments. Such adaptations, which may be sum-
marised as adaptations that increased the scale of activity and improved
environmental resistance, incidentally enabled hominids to expand their

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