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10


Mediterranean
Sites/Millennium




0 Atlantic



Southern Iberia
-10
-40 -30 -20 -10 0
Time (kyr)

(b) 3000




2000
% Differential on previous period




1000



Mediterranean

0

Atlantic



-1000 Southern Iberia
-24 -22 -20 -18 -16 -14 -12 -10 -8
Time (kyr)

Figure 7.8. Changes in site density during the Upper Palaeolithic in different regions
of the Iberian Peninsula. Note the close correspondence between the Mediterranean
and the south (Mediterranean bioclimatic areas) and the sharp contrast with the
Atlantic (Euro-Siberian bioclimatic areas).
172 Neanderthals and Modern Humans

adaptation for steppe conditions. As these environments shrunk so population
densities dropped, ¬rst in the south. This interpretation is in keeping with the
general observation that climate warming is known to affect a northward ex-
panding species™ ability to survive in the south of the range (Bennett et al.,
1991; Hewitt, 1996, 1999). Response to the climatic warming would have been
the use of new technologies, that are evident in the Magdalenian, and an initial
tracking of steppe environments. The latter response would take the form of
a following of these environments up mountains in the south, and Straus &
Winegardner (2000) indeed comment on an increase in mountain sites in the
Magdalenian. In the north there was a population expansion and Straus & Wine-
gardner™s (2000) results show an increase in site density in the Magdalenian
in the Atlantic“Cantabrian region when populations in the south were on the
decline. This phenomenon appears to be part of a wider pattern of northward
expansion at the end of the LGM (Demars, 1996; Torroni et al., 1998; Bocquet-
Appel & Demars, 2000a).


The transition in Iberia

Empirical evidence currently points towards the Iberian Peninsula being one
of the last geographical regions of the planet in which Neanderthals survived
(Vega-Toscano et al., 1988; Antunes et al., 1989; Zilhao, 1993, 1995, 1996;
Raposo & Cardoso, 1998; Finlayson & Giles Pacheco, 2000). More widely,
the causes of the extinction of the Neanderthals are unknown although most
authors link the disappearance with the arrival of Modern Humans in Europe and
western Asia even though evidence of biological superiority of Modern Humans
over Neanderthals, to which many authors still subscribe (see ˜Comments™ in
d™Errico et al., 1998), is non-existent as we have seen in this book. At best
the logic applied in favour of such superiority rests on the circular reasoning
that they (the Moderns) survived and must have therefore been superior (see
˜Comments™ in d™Errico et al., 1998). Nobody is prepared, it seems, to consider
the possibility that the colonisation of Europe by Moderns and the extinction
of the Neanderthals may have been independent events, a position that I have
advanced in this book.
More speci¬cally in Iberia, attempts have been made to link the extinction of
the Neanderthals there with climate change which caused the entry of Modern
Humans into the Iberian Neanderthal refuge (Zilhao, 1996; Finlayson & Giles
Pacheco, 2000). The Iberian Peninsula is particularly well suited for the study of
the ˜transition™ or ˜replacement™ (which I prefer to call ˜extinction:colonisation
processes™, a terminology closer to that of existing theory, MacArthur & Wilson,
1967) given a large surface area, biogeographical distinctness and its ecological
Modern Human colonisation and Neanderthal extinction 173

heterogeneity caused largely by its highly varied relief (Finlayson & Giles
Pacheco, 2000; Finlayson et al., 2000a)
The basis of this section is an ecological model which aims to point at possible
underlying mechanisms for the extinction of the Neanderthals in the Iberian
Peninsula by disentangling the multiplicity of potential variables and analysing
the effect of a small number of suf¬cient parameters (Levins, 1968). By doing
this I hope to establish patterns of wider geographical relevance in support of
the arguments advanced in this book. Most recently, d™Errico et al. (1998) have
called for the need to develop models of what happened to the Neanderthals. If
indeed we are to resolve this question scienti¬cally (Kuhn, 1970) then we must
proceed through the development of testable strategic models and more general
tactical ones (May, 1973; Gillman & Hails, 1997) which form the theoretical
framework upon which empirical evidence must be evaluated.
For this exercise I have divided the Iberian Peninsula into 273 50 — 50-km
Universal Transverse Mercator (UTM) Projection units. A map of the biocli-
matic stages of the Iberian Peninsula (Rivas-Mart´nez, 1987) was superimposed
±
on this grid and a bioclimatic stage was allocated to each unit. In cases where,
for reasons of abrupt relief, more than one bioclimatic stage occurred in a
square the stage which was judged to cover the greatest surface area of the
square was allocated to the square. Four bioclimatic stages were identi¬ed, but
the oro- and crioro-Mediterranean stages (Rivas-Mart´nez, 1981, 1987) are too
±
reduced in area and restricted to certain mountain peaks to be signi¬cant at
the resolution of the model (Figure 7.9a). The four stages I have used (follow-
ing Rivas-Mart´nez, 1981, 1987) are: (1) thermo-Mediterranean, characterised
±
by mean annual temperatures (T) between 17 and 19 —¦ C, mean minima of the
coldest month (m) between 4 and 10 —¦ C and mean maxima (M) of the cold-
est month between 14 and 18 —¦ C; (2) meso-Mediterranean, characterised by T
between 13 and 17 —¦ C, m between ’1 and 4 —¦ C and M between 9 and 14 —¦ C;
(3) supra-Mediterranean, characterised by T between 8 and 13 —¦ C, m between ’4
and ’1 —¦ C and M between 2 and 9 —¦ C; and (4) Euro-Siberian characterised by
T between <3 and 10 —¦ C, m between <’8 and 0 —¦ C and M between <0 and
>8 —¦ C. Elements of the oro- and crioro-Mediterranean stages would have fallen
within supra-Mediterranean stages. The characteristics of these stages are: (1)
oro-Mediterranean, T between 4 and 8 —¦ C, m between ’7 and ’4 —¦ C and M
between 0 and 2 —¦ C; and (2) crioro-Mediterranean, T < 4 —¦ C, m < ’7 —¦ C and
M < 0 —¦ C.
Using the range in T of the different bioclimatic stages, I have calculated how
the proportion of 50 — 50-km units allocated to each bioclimatic stage would
vary with a progressive drop in T from present-day to 10 —¦ C below present at
intervals of 1 —¦ C. The results (Figure 7.9b) indicate that Mediterranean biocli-
matic stages would not disappear altogether at T ’10 —¦ C although only the high
174 Neanderthals and Modern Humans




200
(b)
Surface Area (50x50-km) units




100
Thermo-Med

Supra-Med

Oro-/Crioro-Med

Meso-Med

0 Eurosiberian
0 2 4 6 8 10

Temp Drop

Figure 7.9. Predicted changes in the distribution of Iberian bioclimatic stages with
decreasing annual mean temperatures (T). (a) Present day distribution. (b) Curves
showing changes in bioclimatic stages with decreasing T at 1—¦ intervals.
(c) Distribution of bioclimatic stages at T ’3 —¦ C. (d) Distribution of bioclimatic stages
at T ’9 —¦ C. Black: Euro-Siberian; dark grey: oro/crioro-Mediterranean; medium grey:
supra-Mediterranean; pale grey: meso-Mediterranean; white: thermo-Mediterranean.
Modern Human colonisation and Neanderthal extinction 175


(c)




(d)




Figure 7.9. (cont.)



montane components (oro- and crioro-) would remain. The thermo-Mediterr-
anean Stage disappears at T ’3 —¦ C; the meso-Mediterranean at T ’7 —¦ C; and
the supra-Mediterranean at T ’10 —¦ C although the area covered by this stage
actually increased between T ’1 —¦ C and T ’5 —¦ C. The oro- and crioro-Mediterr-
anean and the Euro-Siberian stages progressively expanded in area with declin-
ing T. The range of T examined encompasses the conditions that would have
been met in Iberia in OIS 3 and 2. In the Massif Central in France, warm OIS 3
events were T ’4 —¦ C and cold events down to between T ’9 —¦ C and T’11 —¦ C.
(Guiot et al., 1989). Using the results from Figure 7.9(b), I have illustrated
176 Neanderthals and Modern Humans

in Figure 7.9(c) the expected distribution of the Iberian bioclimatic stages
at T ’3 —¦ C, a situation that may have been frequent in OIS 3. It re¬‚ects the
elimination of the thermo-Mediterranean stage and the growth of the montane
Mediterranean stages. In Figure 7.9(d) I represent an extreme situation at T
’9 —¦ C, resembling the colder late stages of OIS 3 and the conditions at the
LGM. The dominance of Mediterranean montane stages and the southward
expansion of the Euro-Siberian stages are evident. This pattern ¬ts well with the
observations of environmental change in Iberia that I described in Chapter 6.
In the density-dependent population dynamic models that I introduce here,
growth and range expansion/contraction are related to bioclimatic and geo-
graphical factors. It is important to stress that I use the terms warm-adapted,
cold-adapted, etc. to convey principally the direction of response to climate-
induced habitat change. Thus, a population that reacts positively to an increase
in preferred habitat and that habitat increases as conditions become colder, is
said to be cold-adapted, and so on. In each case the starting point of the model
was selected at 58 kyr for Neanderthal populations and 40 kyr for Moderns. The
¬rst was chosen to cover the spectrum of climatic change of OIS 3 (e.g. van
Andel, 1998; van Andel & Tzedakis, 1998); the second was considered to be
a close approximation to the time when Neanderthal and Modern populations
were sympatric in the north of the Iberian Peninsula (Mellars, 1996) and close to
the point of ¬rst appearance of Moderns in Iberia. From these points population
levels could be estimated forward or backward in time. The assigned ages are
therefore model-dependent throughout. Depending on whether the simulation
being run assumed that the population showed a preference for warm or cold
conditions the starting population size was varied for each bioclimatic stage.
Thus, for Neanderthal simulations at 58 kyr the starting population sizes allo-
cated for each of the 273 cells were set at 100, 75, 50 and 25 population units
ranked by bioclimatic stages. Thus, if the model considered the population to
be warm-adapted the thermo-Mediterranean stages would have a starting pop-
ulation level of 100 and the Euro-Siberian a starting population level of 25 and
vice-versa. Reversing the order of the initial population had a negligible effect
on the model outcome. Figure 7.10 shows, for example, that the extinction of
the warm-adapted Neanderthal population occurred within a 1-kyr period with
the two extreme starting population sizes. Sensitivity analysis further empha-
sised the model™s robusticity, the starting population contributing 1.4% to the
variance of the outcome. The effect of stochasticity on the model outcomes was
tested by running Monte Carlo simulations (1000 trials). For the warm-adapted
Neanderthal model the population became extinct at the simulated outcome
time in the deterministic model on 47.3% of the trials. For the remainder, the
population size had fallen to under 3 and was thus in imminent danger of
Modern Human colonisation and Neanderthal extinction 177

30000




20000




10000
Population Size




Warm Adapted
Reversed

Warm Adapted
0
-60 -50 -40 -30 -20

Time (kyr BP)

Figure 7.10. Simulated evolution of the Iberian Neanderthal population with starting
populations described in the text (warm adapted) and with starting populations
reversed (warm adapted reversed).

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