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tropical human populations would have repeatedly reached south-west Asia,
the range expansion sometimes being checked by changing climate.
Geographical barriers would have then played a major role in the continuing
expansion of the geographical range. In the west, the Strait of Gibraltar appears
to have acted as a barrier on a number of occasions but not necessarily always
(Finlayson et al., 2000a). Thus the similarity in Acheulian technology on the two
shores of the Strait has led some authors to postulate that movement did occur at
such times (Alimen, 1975; Giles Pacheco & Santiago P©rez, 1987). In the east,
Human range expansions, contractions and extinctions 47

the barriers of the Taurus, Pontic, Zagros and Caucasus would have checked the
expansion of the tropical humans (Finlayson et al., 2000a). Warm conditions
would have restricted movement here because much of the landscape would
have been densely wooded and unsuitable for expanding human populations.
Cold conditions would have been just as unsuitable as montane habitats reached
close to the shore. Passage could have occurred along river valleys or along the
extended coastal shelf during intermediate climates, most probably immediately
after cold phases when southern populations would have been augmenting and
the forests had not closed up. Passage east from the Middle East or the Horn
of Africa would have been much easier. The eastward spread would have kept
populations south of the Himalayan mountain mass and within tropical or semi-
tropical climates. Finlayson et al. (2000a) predicted that the frequency of range
expansions from Africa into different parts of the world would have followed
the sequence (Figure 3.1) discussed below.


Sahara, Middle East and southern Africa

These areas would have received expanding populations most frequently on
account of similarity of climate and proximity to source areas. North-west
Africa, however, belonged in the next category because of the combined effect
of distance from source areas and the Sahara Desert.


South to South-east Asia, north-west Africa and south-east Europe

These areas would have been next in frequency of colonisations because of
climatic similarity, and relative ease of access. Some areas would have been
relatively close to source areas but others relatively distant. Australia is a natural
extension of this belt on the South-east Asian side but would only have been
colonised once the sea barrier could be overcome, occurring substantially earlier
than 50 kyr (Thorne et al., 1999; Bowler et al., 2003). South-east Europe falls
into this category because of climate similarity and proximity and does not
appear in the previous category with the Middle East because of the effect of
the intervening mountain barriers.


Central and western Mediterranean Europe and the
Eurasian Plain

These would have been the next areas to be colonised, increasing distance from
source areas and mountain barriers, delaying access. In the earlier colonisations
48 Neanderthals and Modern Humans

only the Mediterranean and adjacent lands were colonised, the Plains being the
last to be reached (Chapter 7). Climatic difference from source areas appears not
to have been an impediment, at least to the later expanding populations, because
of the structural similarity of these environments to those of the source areas
and also the availability of mammalian herbivores (Chapter 2). The climatically
more suitable areas of the central and western Mediterranean are also included
in this category because of their distance from source areas, especially when the
Strait of Gibraltar acted as a barrier. I consider much of North America to be,
in human terms, an extension of the Eurasian Plain (Chapter 2). Once humans
reached eastern Siberia, only the Bering Strait would have prevented access to
this sector at certain times.
The Middle East has been the predominant terrestrial access channel from
Africa into Eurasia but the alternative route via the Horn of Africa may have
been a signi¬cant alternative at times (Lahr & Foley, 1994; Quintana-Murci
et al., 1999). The early colonisations of eastern Asia by populations ancestral
to those de¬ned as H. erectus around 1.9“1.8 Myr (Klein, 1999; Aguirre &
Carbonell, 2001) and western Asia by H. ergaster with Mode 1 technology
around 1.7 Myr (Gabunia et al., 2000, 2001; Bar-Yosef & Belfer-Cohen, 2001)
are in keeping with this view. A further expansion (or expansions) of hominds
with Mode 2 technology, appears to have reached the Middle East around 1.5“
1.4 Myr (Aguirre & Carbonell, 2001; Belmaker et al., 2002) and north-west
Africa by 1 Myr (Raynal et al., 2001). A subsequent colonisation around 800“
500 kyr (probably 600 kyr) by hominids with Mode 2 technology, via the Middle
East (Bar-Yosef & Belfer-Cohen, 2001), appears to have reached China (Hou
et al., 2000) as well as Europe (Aguirre & Carbonell, 2001) and may have
included passage across the Strait of Gibraltar (Alimen 1975; Giles Pacheco &
Santiago P©rez, 1987). Another possible expansion around 250“200 kyr, by a
population claimed to belong to H. helmei with Levallois technology, could
have reached Europe via the Middle East (Foley & Lahr, 1997; Porat et al.,
2002) and may have originated the Neanderthal line. A further expansion after
100 kyr, this time by Modern Humans, ¬rst spread eastwards across the tropical
Asian belt and led to the colonisation of Australia before 50 kyr (Thorne et al.,
1999; Bowler et al., 2003), the colonisation of Europe by at least 45 kyr (Klein,
1999) and the subsequent expansion across the Eurasian Plain, including for
the ¬rst time North America. These are just some expansion markers in what
would have been a more ¬‚uid and continuous system of range expansion and
contraction over the last 2 Myr (Finlayson et al., 2000a).
Populations that reached geographical areas away from tropical Africa would
have differentiated and adapted to local conditions. The success of adaptation
would have depended on the climatic and environmental stability of each area.
More stable areas would have permitted populations to persist and reach den-
sities close to carrying capacity. Populations with more restricted geographic
Human range expansions, contractions and extinctions 49

ranges would have been most prone to extinction whereas those with greater
mobility and behavioural diversity persisted (Potts, 1996a, b, 1998). Homo erec-
tus may have survived until 25 kyr in parts of tropical South-east Asia (Swisher
et al., 1996). These would be the areas least affected by cold and aridity, prob-
ably more so than even tropical Africa (Pope, 1983). It is possible that the
H. helmei expansion (Foley & Lahr, 1997) did not reach South-east Asia be-
cause of the vicissitudes of climate. If they did reach they may have been unable
to establish themselves because of competition from established local popula-
tions, a theme that was probably recurrent in human dispersal throughout the
Pleistocene.
Populations in mid-latitudes and on the Eurasian Plain would have survived
by expanding the range northwards during warm events and contracting south
during cold arid ones (Finlayson et al., 2000a; Hewitt, 2000). Some of these
populations may have been present when the next populations of colonisers
arrived. It is possible that populations attributed to H. heidelbergensis and
H. helmei would have been present in Europe at the same time (Foley & Lahr,
1997) and this was also the case between Modern Humans and Neanderthals.
Increasingly, frequent cold and arid periods removed these populations from
Europe and western Asia. The western European populations were constrained
by the Strait of Gibraltar and repeatedly became extinct, a situation experienced
by many other animals (Busack, 1986). The south-eastern European, or south-
west Asian, populations of Neanderthals were apparently able to expand the
range south into the Middle East (Tchernov, 1998) but the Sahara would have
prevented further expansion to the south. It was only in South-east Asia that trop-
ical refugia allowed persistence outside Africa. The populations that settled in
Europe and north-western and central Asia could only maintain core geographi-
cal areas in the south (Gamble, 1999), across the topographically heterogeneous
mid-latitude belt from Iberia to the Caucasus and beyond to the Altai (Figure
2.1). As such they evolved adaptations to a different way of life from that of the
plains. These populations lived in areas where several ecological zones were in
close proximity (Soffer, 1994) and where warm temperate climates permitted a
varied dietary subsistence that resembled, though less varied, that in the tropics.
Such conditions spread north during warm events and the humans tracked these.
The extinction of the Neanderthals towards the end of Oxygen Isotope Stage
(OIS) 3, when conditions were not as severe as earlier in the late Pleistocene,
was the product of a series of cold and arid events which had the combined
effect of suppressing and fragmenting Neanderthal populations (Chapter 7).
Such periods of population contraction (bottlenecks) and expansions might also
have had an effect on the genetic divergence of isolated lineages (Lahr & Foley,
1998, Hewitt, 1996, 1999, 2000). Open plains hunting strategies were, as a rule,
evolved in the African plains. Such strategies pre-adapted African populations
to exploit the structurally similar conditions of the Eurasian Plain, provided
50 Neanderthals and Modern Humans

they could get there across the mountainous mid-latitude belt. Once estab-
lished there, they could persist until extreme cold events forced them south into
refugia.
The history of human demography and geographical dispersion can therefore
ultimately be explained in terms of climate change causing vegetation change
in turn causing change in the distribution and abundance of animals, particu-
larly mammalian herbivores (Chapter 2). Very rarely is a direct climate“human
population effect expected. Rather, it is the effect of climate on available habi-
tats and resources that is the mechanism producing change. The question of
human history in the late Pleistocene has a strong spatio-temporal, multi-scale,
component in which events are nested within others at different scales that may
even appear to be operating in reverse directions. Such situations would have
created spatio-temporal mosaics in the distribution and abundance of human
populations which are closer to expectations from ecological and evolutionary
theory than the currently available views of a single or small number of discrete
events (dispersals/migrations) that are proposed for the origins of ˜modern™ hu-
mans and their dispersal across the globe. To such mosaics must be added the
strong cumulative temporal components that are often disregarded in issues of
human origins.
Populations of humans therefore colonised areas of the Old World from
Africa as from 1.9 Myr bp. A major contributing factor to this expansion was the
habitual exploitation of an increasingly carnivorous diet (Gamble, 1995; Lahr &
Foley, 1998, Stanford, 1999; Stanford & Bunn, 2001). On reaching mid-
temperate latitudes of the Northern Hemisphere these humans were in areas
that had the highest net primary productivity after regions near the Equator,
although today, for example, the productivity peak is con¬ned to the period
from April to September (Field et al., 1998). Other populations (e.g. heidelber-
gensis) would have followed (Lahr & Foley, 1998). Moderns and Neanderthals
may have been separated by 500 kyr (Stringer, 1989) or less, if there was a
subsequent expansion from Africa of humans with Mode 3 technology around
250 kyr (Foley & Lahr, 1997). Successive isolations, caused by the ¬‚uctu-
ating climates of the Pleistocene, differentiated these populations genetically
and phenotypically although the timescales involved were in all probability
insuf¬cient for speciation to have occurred. This means that there would have
been gene ¬‚ow between populations at certain times (Lahr & Foley, 1998)
and these populations may have held fairly stable hybrid zones (Cain, 1971,
Hewitt, 1996, 1999, 2000). The cumulative effects of successive isolations
built on the genetic differences. A similar, but more limited because of the
timescales involved, genetic differentiation after the Last Glacial Maximum
(LGM) between Moderns in different parts of the Earth followed the earlier
pattern.
Human range expansions, contractions and extinctions 51

Earlier in the late Pleistocene one of these forms increasingly became a
large mammal hunter of the East African plains. Its geographical range ex-
panded as savannahs and grasslands gained over tropical rainforests during
cold and arid phases (Foley, 1987; Foley & Lee, 1989; de Menocal, 1995). Dur-
ing one or more milder and wetter phases the Saharan barrier broke down and
their range extended into the Middle East. At such times the pressure would
have been for northward range expansion into these new areas of grassland
and savannah as existing areas to the south returned to forest. Similar expan-
sions may have occurred during the cool conditions around 500“450 kyr, when
H. heidelbergensis with Mode 2 (Acheulian) technology reached Europe (Klein,
1995; Lahr & Foley, 1998) and at the end of another cold period around 250
kyr when humans (attributed to H. helmei) with Mode 3 (Levallois) technology
spread (Foley & Lahr, 1997; Lahr & Foley, 1998).
The mountains of Turkey and the Caucasus acted, as we have seen, as
formidable barriers to range expansion but eastward dispersal was not impeded
by barriers. Once across the western Asian mountains, African plains people
found habitats in the Eurasian Plain structurally analogous to their East African
original habitats and they were able to rapidly colonise. As these environments
expanded with increasing cold and aridity, plains-adapted humans followed
(Woillard, 1978; Suc & Zagwijn, 1983; Gamble, 1986, 1999; Roebroeks et al.,
1992; Zagwijn, 1992). This explains, in my view, why Moderns expanded. It
is not expansion that ˜occurs against the grain of climatic change™ (Lahr &
Foley, 1998). In Europe the local form, the Neanderthal, exploited highly het-
erogeneous landscapes principally in the south. These were the only areas
that could sustain populations throughout a glacial“interglacial cycle (Gamble,
1999). During warm interglacials, the Neanderthals™ range expanded north-
wards reaching its highest during, or just prior to and just after (when dense
forests had not established themselves, Roebroeks et al., 1992; Gamble, 1999),
the last interglacial and coinciding with the establishment of the Mousterian
technology (Foley & Lahr, 1997). The brevity of such events and gene ¬‚ow
with contiguous populations to the south precluded adaptation to the North
Eurasian Plains environments, especially as much of the landscape would have
been wooded (Roebroeks et al., 1992; Gamble, 1999). The progressive cooling
after the last interglacial gradually reduced the range of the Neanderthals.


The European case

The number of hominid dispersals from Africa into Europe that led to success-
ful colonisations into Europe varied, depending on the author, between a single
ancient event (Wolpoff, 1989), through two events involving H. ergaster and
52 Neanderthals and Modern Humans


.5
Warmer


0.0


-.5


-1.0


-1.5


-2.0
Mean δ18O




-2.5

Colder
-3.0
-80 -70 -60 -50 -40 -30 -20 -10 0
Time (Myr)

Figure 3.2. Decrease in temperature during the last 70 Myr. Regression model y =
’2.3029 + 0.0284x + 0.0028x2 + (2.6 — 10 ’ 5x)3 . The relationship is statistically
signi¬cant (R2 = 0.955, P = 0.016). After Finlayson (2003).



H. sapiens (Klein, 1999) to up to four involving H. ergaster, H. heidelbergen-
sis, H. helmei and H. sapiens (Foley & Lahr, 1997). In the latter case, Foley &
Lahr (1997) have linked the four events to the introduction of technological
modes 1 to 4 respectively. The fate of these populations on reaching Europe
is also unclear. Although there are claims for the presence of Homo in Europe
before 1 Myr (Martinez Navarro, 1997; Oms et al., 2000), the earliest well-

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