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There are several points that will be of particular importance to the discussion
of Modern Human colonisation and Neanderthal extinction in the following
chapter. In global terms the last glacial cycle was the coolest and most variable
of the Pleistocene with wide climatic ¬‚uctuations that were particularly bad
during glacial maxima. Climate oscillations occurred across a range of tempo-
ral scales, including small scale annual to decadal, and transitions were abrupt.
The greater part of the cycle was dominated by climatic conditions that were
intermediate between those of glacials and interglacials. Sea-levels ¬‚uctuated
between highstands of +2 to +12 m and lowstands of ’118 to ’135 m. During
the long, intermediate, conditions of OIS 3 sea-levels oscillated around ’80 m.
146 Neanderthals and Modern Humans




Figure 6.2. Predicted major vegetation transitions in relation to late Pleistocene
climate. Bioclimate boundaries as in Figure 5.3. M-D, Mediterranean
vegetation“desert transitions; M-S, Mediterranean vegetation“steppe transitions; T>,
temperate forest intrusions during warm and wet climate; <S, steppe intrusions during
cold and arid climate; T V, tundra intrusions during cold and arid climate.


The signi¬cance of these changes was in the exposure of large areas of conti-
nental shelf and not in the opening up of land bridges (the Strait of Gibraltar,
for example, narrowed but remained open throughout). In the Mediterranean,
areas of exposed coastal shelf would have been within the most benign climate
regimes and would have therefore contributed to the surface area of refugia.
Vegetation responses took the form of open vegetation“woodland transitions
across the western Eurasian Plain (Figure 6.2). The greater part of OIS 3 was
treeless from the British Isles to the Russian Plain. Woodland only therefore
covered large areas of the Plain for short periods of the glacial cycle. In the
Mediterranean, where moisture“aridity gradients were particularly critical, the
pattern was more complex on account of topographical heterogeneity with sig-
ni¬cant local differences in vegetation patterns and responses. Generalisations
are impossible and each area has to be understood independently. This even
applies within the peninsulas, especially in the Iberian Peninsula. OIS 3, in
particular, is complex with moments of expansion of Mediterranean taxa in
Africa and Eurasia during the last glacial cycle 147

some areas and of steppe vegetation expansion in others, adding a spatial com-
ponent to the climatic unpredictability (Figure 6.2).
North Atlantic sea-surface temperatures played a signi¬cant role in mod-
ulating climate, and vegetation changes took the form of woodland“steppe
transitions, altitudinal movements of plant species, contraction and expansion
of Mediterranean thermophyllous species and shifts in the dominance of broad-
leaved and coniferous woodland. In the coldest moments, North Atlantic marine
mammals and birds reached the Strait of Gibraltar. The Mediterranean penin-
sulas were pivotal as glacial refugia for Mediterranean and temperate vegeta-
tion but the Middle East appears to have been less important on account of
long periods of high aridity. There were important differences between refu-
gia, the Italian and Balkan refugia being especially important for temperate
broad-leaved trees, and Iberia for Mediterranean taxa. The African coast of
the Mediterranean came under the in¬‚uence of desert and semi-desert during
arid periods related to cold events with the expansion of Mediterranean wood-
land, especially in the north-west, during interglacials. The African picture was
dominated by rain“arid cycles with swift vegetation responses. The northward
and southward shifts in the belts of desert, grassland and savannah repeatedly
opened and closed the door between tropical Africa and the Mediterranean.
7 The Modern Human colonisation and
the Neanderthal extinction

There are repeating patterns that we can observe among a wide range of
organisms that occupied Pleistocene Europe. These include the contraction
into southern refugia and subsequent expansions during climatic amelioration
that I shall describe in this chapter. In seeking a generalised theory that accounts
for the varying fortunes of the Neanderthals and Moderns we must consider that
Pleistocene people were humans, not super-humans. By this I mean that, even
though humans in the Pleistocene had succeeded in evolving socio-cultural
and technological achievements that undoubtedly set them apart and gave them
great advantages over the other animals with which they shared territory, they
were by no means independent of the environment that surrounded them and
were very much subject to the forces of natural selection. If we are able to
see similarities of pattern with other Pleistocene animals then we will have ad-
vanced towards a generalised theory. If we are unable to ¬nd such similarities
then we will also have advanced in our understanding of the distinctness of
humans in the Pleistocene world.


Humans, climate and environmental change

Eurasian humans throughout the Pleistocene were restricted to southern refugia
during cold episodes. The degree of permanence of human populations would
have been highest in tropical and equatorial regions with decreasing probability
of permanence away from these areas (Finlayson et al., 2000a). The most sig-
ni¬cant general pattern is the permanence of many species along the southern
part of the European range in the Mediterranean peninsulas of Iberia and the
Balkans, in particular, and the temporary and often brief range extensions into
northern lands (Hewitt 1999, 2000). Every time the glaciers and ice sheets
advanced so populations were con¬ned to the Mediterranean refugia. That
humans responded in the same manner as most other organisms is undeni-
able and it affected Neanderthals and Moderns as it no doubt affected their
predecessors. The Neanderthals (including their European ancestors) survived
in Europe (Figure 5.3) for over 400 kyr but it is important to note that they:



148
Modern Human colonisation and Neanderthal extinction 149

(1) only occupied areas of the central and western European Plain during
milder events;
(2) they never colonised the steppes of eastern Europe;
(3) They were restricted to the Mediterranean peninsulas (and Crimea and the
Caucasus) during the colder episodes.
Neanderthals therefore were restricted to southern refugia during cold and arid
events and they were unable to recover from the last of these (Finlayson et al.,
2000a). Moderns were not much better at dealing with the glaciations. The ¬rst
major glacial advance that hit them in Europe forced them into the same southern
retreats that Neanderthals had entered previously. They managed to hold out,
just as populations of Neanderthals had done during earlier cold events, and
subsequently they spread north (Torroni et al., 1998, 2001). Humans have not
experienced another cold episode since. The observed pattern for Neanderthals
is therefore no different from that of other human populations, including the
Moderns, and is part of a recurring theme.
In my view this sets the large-scale spatial and temporal scenario that best
explains the changes in human populations that occurred in Europe and Asia
throughout the Pleistocene. In an earlier paper (Finlayson et al., 2000a) I have
indicated the conditions that would have favoured the spread of human popula-
tions from tropical Africa into the Middle East and from there towards Asia and
Europe (see also Chapter 3). I have also proposed that, once in South-east Asia,
human populations would have achieved degrees of permanence comparable
to the African populations and such populations would have functioned as sec-
ondary sources from which temperate Asian populations were fed (Chapter 3).
The case for continuity in human evolution is strongest in equatorial and
tropical areas of the world. Given that the origin of the lineage that led to the
Moderns was African (Chapter 4), we should observe the longest period of
continuous human occupation in that continent. This should be followed by
tropical and equatorial Asia, the difference with Africa being historical. The
degree of persistence of human populations away from these areas at any given
time would have varied with latitude and altitude. The ability to colonise and
persist further and further away from the tropics improved through time. Be-
havioural mechanisms evolved in the open tropical savannahs that pre-adapted
populations for colonisation away from the tropics. I predict therefore that ex-
tinction of local and regional human populations was probably a feature of
non-tropical areas and that the probability of extinction decreased with time.
The extinction of a human population, such as the Neanderthals, in Eura-
sia during the Pleistocene would not have been a singular event (Finlayson,
2003). The ultimate causes of human population extinctions in the Pleistocene
150 Neanderthals and Modern Humans

are probably very similar in all cases. Populations in southern refugia became
fragmented and were unable to recover. Climatic conditions, acting on habitats
and resources, were primarily responsible for range contractions and popula-
tion fragmentation and reduction (Finlayson et al., 2000a). The probability of
persisting through a bad event would have depended on the intensity of the bad
event, the frequency of bad events, the intensity and length of intermediate good
events allowing population recovery, initial population size and demographic
and genetic population parameters. Socio-cultural and technological attributes
may have alleviated situations in some circumstances (Gamble, 1999).
A single proximate cause of local and regional human population extinc-
tions in the Pleistocene is unlikely. The retreating rear edge of a range during
a period of contraction will be expected to suffer severe shrinkage, dissection
and extinction with a severely bottlenecked last surviving population (Hewitt,
2000). Once human populations became fragmented and depressed to the point
of imminent extinction, the ¬nal cause of extinction would have varied from one
situation to the next. Proximate extinction causes could have included stochastic
processes, local inbreeding, competition, habitat and resource fragmentation,
Allee effects, disease and reduced immunity (Figure 7.1). It is therefore point-
less, given current data resolution, to seek a single proximate solution to explain
the extinction of the Neanderthals, or indeed any other human group.
Before changing the subject I want to discuss one ¬nal point, and a crucial
one, in understanding extinction. This is the effect of frequency as well as inten-
sity of environmental ¬‚uctuations, time lags and cumulative effects. A number
of authors have sought direct correlations between environmental ¬‚uctuations
and demographic changes. People have looked at climate curves and attempted
to prove or disprove effects on populations by seeking direct matches between
the two. These have produced con¬‚icting results when trying to interpret the
effect of climate on human population dynamics and especially the Neanderthal
extinction (e.g. Courty & Vallverdu, 2001). The absence of a correlation need
not, for example, be evidence for no environmental effect. Environmental ef-
fects may be expressed in many ways and at different scales. In the case of
the Neanderthal extinction we are looking at a large scale effect that depresses
populations globally and the effect is caused by an increase in frequency of
climatic oscillations, i.e. increasing instability. Why did the Neanderthals not
become extinct earlier during a similar period? This presupposes that, for ex-
ample, starting population sizes were equivalent before each perturbation. Put
simply, the effect of 50% population reduction in a population of 10 000 may
allow recovery but the same effect on a population of 100 may well lead to
extinction. Theory predicts that in the case of two species with different coloni-
sation (c) and extinction (e) rates but equal c/e values, the species with higher
c and e values will reach a new equilibrium after habitat destruction faster than
Modern Human colonisation and Neanderthal extinction 151


DISEASE



STOCHASTIC




ALLEE
EFFECT




LARGE
POPULATION


INSUFFICIENT
RESOURCES




OUTCOMPETED

INBREEDING



GENETICALLY
SWAMPED

Figure 7.1. Potential causes of extinction of local populations fragmented from a
hypothetical large parent population.



one with lower c and e. This is an example of relaxation in which the new
equilibrium level of patch occupancy is not reached instantly. We may say that
the species exists as ˜living dead™ (Gilpin & Soul©, 1986; Groom & Pascual,
1998). So matching the moment of extinction with an environmental event at
that moment would be absurd! The irony is that the species might actually be-
come extinct during favourable climatic conditions! There is a practical point
152 Neanderthals and Modern Humans

that we must also consider. That last Neanderthal populations on record occur
around 31“28 kyr. Trying to match precise climatic conditions to these dates is
not only unrealistic, because of what I have said so far, but also because these
are not real extinction dates. These are dates when populations were still high
enough for us to detect them in the archaeological record. So, as with other
things we have looked at so far, we can only look at the Neanderthal extinction
from a large-scale perspective because we simply do not have the resolution to
go further. Some people may persist in trying to ¬nd the cause of the death of
˜the last of the Neanderthals™. It is like looking for the missing link. I prefer to
stay with the view that high environmental instability depressed and fragmented
their populations at the end of Oxygen Isotope Stage (OIS) 3 beyond recovery.
Such a view has theoretical and empirical support. If the rate of environmental
movement is slow, species will be expected to track their particular environ-
ments across space as geographical range changes are more malleable than
morphology or environmental tolerance (Pease et al., 1989). The Neanderthals
appear to have tracked their environments in this way. When the rate of change
intensi¬ed towards the end of OIS 3, they went extinct.


Competition

Competition structures communities that are in equilibrium and is not impor-
tant in situations of wide environmental ¬‚uctuations and unpredictable distur-
bance (Wang et al., 2002). Finlayson et al. (2000a) have clari¬ed the situations
in which ecological competition was likely to have occurred in Late Pleis-
tocene Europe and western Asia and came to the conclusion that, if it ever
took place at all, competition between Neanderthals and Moderns would have
been ephemeral and would not have determined the ¬nal outcome of the two
populations. Similar situations would have arisen in other parts of the world.
Rolland (1998) and Richards et al. (1998) comment on the sparse, low-density,
population pattern for Eurasia in the Pleistocene, suggesting that demographic
carrying capacity was not attained, and have contrasted this with the situation
in Africa. Harpending et al. (1998) estimated the effective human population
size not to have exceeded 10 000 for most of the Pleistocene.
Van Peer (1998) found two coexisting (archaic and modern) populations in
north-east Africa in the late Pleistocene. One (archaic) was exclusively riverine-
adapted and only occasionally used desert. The other (modern) allowed popu-
lations to adapt to varied environments, including the desert. Occasionally, de-

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