<<

. 16
( 43 .)



>>

tion to the evolution of Moderns has obscured the processes by which Moderns
evolved (Foley, 1989). Patterns of hominid evolution and the key elements of
Modern Human behaviour are explicable in terms of the general principles of
evolutionary ecology (Foley, 1992).
The Out-of-Africa and multiregional perspectives are inadequate and have
been cited as an example of a pre-paradigm scienti¬c dispute (Strkalj, 2000).
The Out-of-Africa postulate is not a formal theory but a bundle of inferences,
supported by a range of evidence, while the multiregional perspective is a
restatement of the single species model and is untestable (Foley, 1998). A
central problem today is the absence of a coherent interdisciplinary approach
and a uni¬ed theory of human evolution is urgently required. Such a theory needs
to bring together the wealth of new information that is emerging from many
different disciplines and make testable predictions that will give focus to future
research. For it to be effective it must take the form of theory development,
hypothesis testing and pattern seeking, and research must focus at multiple
levels. I attempt to do this in this book.
Fossils cannot tell their own story and they need the comparative perspec-
tive of evolutionary biology. To progress towards a comprehensive and uni¬ed
theory of human evolution we must have, as our base, a life sciences approach
that links theory and mechanism (Foley, 2001). It must depart from the level
at which selective processes operate “ that of the individual. The confusion
that is apparent in sectors of the palaeoanthropological community with regard
to the roles of micro- and macro-evolutionary processes and the dismissal of
the neo-Darwinian synthesis reveals a basic misunderstanding of the process of
evolution (Tattersall, 2000; Foley, 2001). I am in general agreement with Foley™s
(2001) view. There is no need to invoke a special, non-Darwinian, mechanism
to account for species diversity “ in any case no satisfactory mechanism has
been proposed. I also agree with Foley (2001) in his ˜branching tree™ view of
human evolution. Where I differ is in my perception of the nature of the process.
Branching and speciation are not inevitable consequences even if often they are
the result. There are many examples of lineages that have not diverged, but
have evolved or remained relatively unchanged over very long periods. I am
not convinced either that all branchings automatically re¬‚ect speciation events.
This is why I have, returning to Mayr™s (1950) conclusion, stated in this chapter
that there was a single, unparalleled speciation event, that led to the emergence
of the Homo lineage. Between the view of a single, evolving, species and a tree
full of species lies a view of diverging lineages, many of which do not make it
to species status, extinctions and genetic intermixing. In my view we should be
in agreement if we replace ˜species diversity™ by ˜genetic diversity™. The evolu-
tion of Homo in the Pleistocene is marked by increases and declines in genetic
90 Neanderthals and Modern Humans

diversity associated with demographic ¬‚uctuations, colonisation events and ex-
tinctions. If we view the world as one in which lineages continuously increase
in diversity, we run the risk of seeing it as a world in which the trend towards
diversity replaces other, antiquated, perspectives of directional evolution.
I agree with Foley™s (2001) view of the role of demography and geography
in providing the link between local and large-scale processes. To understand
human evolution we must ¬rst understand the small-scale ecological processes
in operation, next the macro-ecological ones, and ¬nally the biogeographic pat-
terns that re¬‚ect the outcomes of the smaller-scale processes. The problem lies
in that we do not have the resolution to detect the small-scale patterns. We can
partly resolve this by establishing larger-scale patterns and interpreting them
within a theoretical framework of known multi-scale patterns and processes
(Finlayson, 1999). The growth and shrinkage of populations are the result of
the sum of the successes and failures of the individuals that form these popu-
lations. Where many populations are successful we have a successful species.
The opposite is species extinction. The process of natural selection acting on
individuals thus leads to multi-scale outcomes, from the success or demise of
individuals, to that of local populations, regional populations and, ultimately,
the permanence or extinction of species. In this book I am concerned, at one
level, with the factors that led to the success and permanence (until now) of
Moderns and the extinction of the Neanderthals. We may be looking at species-
level patterns, in which case the loss of the Neanderthals would represent the
extinction of a species, or lower-level patterns such as the extinction of the
European populations of a form of Homo. Either way, understanding the pro-
cesses at work is my goal. At another level we have the causes of the extinctions
of the separate sub-populations that made up the European Neanderthal popula-
tion. There may be many, small-scale, causes and these will be more dif¬cult to
discern, primarily because we lack the necessary archaeological, palaeontolog-
ical and dating resolution. Too often issues of Modern success and Neanderthal
extinction are pitched at this lower, largely unresolvable, level which may ex-
plain the sterile debate that has dominated the subject.


Synthesis

In this chapter we have commenced our focus on the Eurasian“African system
that generated the Neanderthals and the Moderns that will be the focus for the
rest of the book. We have identi¬ed the following features:

(1) Human evolution need not be seen in the polarised ˜multiregional™ vs ˜re-
placement™ perspectives. The conclusions reached in Chapter 3 regarding
the dynamics of colonisations, range shifts and extinctions form the basis
Modern Human“Neanderthal problem 91

for a model that predicts a range of possible outcomes. It puts particular
emphasis on extinctions and subsequent re-colonisations, the frequency
of extinctions being related to environmental ¬‚uctuations, the abilities of
hominid populations to persist and contingent demographic and spatial
circumstances.
(2) Genetic evidence con¬rms some of the colonisation events predicted in
Chapter 3. Three major expansions from Africa are predicted: around 1.9
Myr; 840“420 kyr (probably 500 kyr); and 150“80 kyr. The latter may
be subdivided into three expansions: 120“100 kyr to South-east Asia and
then Oceania via the Horn of Africa; 60“40 kyr to East Asia and then
north-east Asia and North America via the Middle East; and 60“40 kyr to
western and central Asia and then to Europe.
(3) With this evidence I have produced a revised table of African“Eurasian
events over the last 2 Myr (Table 4.1). The following signi¬cant periods
are identi¬ed:
a. (Events 1“3) 2 Myr-0.95 myr covering many warm periods from OIS 71
to 25. There is at least one major colonisation involving ergaster/erectus
that reaches eastern Asia, the Caucasus and possibly Iberia. There may
have been several such events or instead subsequent cultural diffusion
(including the expansion of Mode 2) and gene ¬‚ow. Further clari¬cation
is required;
b. (Events 5, 7) two periods of possible gene ¬‚ow coinciding with OIS 21
and 17;
c. (Events 9“10) a major colonisation event around 500 kyr, coinciding
with OIS 15, involving heidelbergensis and subsequent gene ¬‚ow dur-
ing OIS 13. The Neanderthals would have evolved from this population
as predicted by Arsuaga et al. (1997);
d. (Events 12“14) a period of possible gene ¬‚ow coinciding with OIS
11“9 followed by the arrival of Mode 3 technology in OIS 7 that
appears to occur through cultural diffusion and gene ¬‚ow and not a
colonisation event. This is followed by the colonisation of south-west
Asia by Moderns in OIS 5 and the subsequent expansion to South-east
Asia and Australia;
e. (Event 16) colonisation and diffusion events after 10 kyr associated
with Neolithic expansions. Once again, the Modern expansions and the
spread of Mode 4 are unrelated to the type of environmental conditions
that would predict African movements. It is therefore most likely that
the 60“40 kyr expansions are of Modern populations that had arrived
in south-west Asia in OIS 5 and subsequently expanded from there. It
also indicates that the early Upper Palaeolithic Eurasian technologies
were not of African origin but instead re¬‚ected adaptations to plains
environments in Eurasia.
Table 4.1. Predicted major expansions from Africa into Eurasia (dark grey rows). Pale grey rows are additional periods of
potential gene flow. Note the predicted potential in the period 2“1 Myr. The period 1“0 Myr includes periods of potential
isolation, range contraction and extinction (white). Event 16 refers to the Neolithic expansions in OIS 1. Note there is no other
suitable moment for African colonisation in Event 16 which reinforces the view that the colonisation of Eurasia by Moderns
was an Asian expansion. (See also text)

Event Time period (Myr) OIS Colonisation Cultural diffusion Gene flow Hominid Technology

ergaster/erectus
1 2.0“1.5 71“49 1
+ + +
ergaster/erectus
2 1.5“1.0 47“27 2
+ + +
3 1.0“0.95 25 +
4 0.95“0.8
5 0.8“0.75 21 +
6 0.75“0.7
7 0.7“0.65 17 +
8 0.65“0.6
heidelbergensis
9 0.6“0.55 15 +
10 0.55“0.5 13 +
11 0.5“0.45
12 0.45“0.25 11“9 +
13 0.25“0.2 7 3
+ +
14 0.2“0.1 7“5 early sapiens
+
15 0.1“0.05
sapiens
16 0.05(0.01)“0 1 4/Neolithic
+ + +
Modern Human“Neanderthal problem 93

(4) Gene ¬‚ow between African and Eurasian populations is predicted to have
been possible for approximately 87.5% of the time in the last 2 Myr (Table
4.1). Gene ¬‚ow appears possible for the entire period from 2 Myr to 1 Myr
and for 75% of the period 1 Myr to the present. Lineage differentiation
can occur in situations of gene ¬‚ow. Thus prolonged periods of gene ¬‚ow
between African and Eurasian populations are not incompatible with the
observed differentiation between Modern Humans and Neanderthals. The
Modern Human and Neanderthal lineages split around 500 kyr, probably
coinciding with the arrival in Europe of the ancestors of the Neanderthals,
but the evidence required to justify their separation as distinct species
is unavailable. Human populations across the globe at any point in the
Quaternary are best regarded as forming a polytypic species with varying
levels of genetic distinctness between each population.
(5) Modern Humans and Neanderthals were sympatric for long periods in
certain areas, most notably the Middle East. A similar situation, requir-
ing study, may have occurred in South, east and South-east Asia between
Moderns and archaic ˜erectus™ humans. The various forms within a geo-
graphical area appear to have behaved as ecotypes. Hybridisation in areas
of geographical overlap is likely but supporting evidence is required.
(6) Modern Humans and Neanderthals exhibit very low genetic diversity
which suggests that these populations went through signi¬cant bottlenecks
during their evolutionary history. Such bottlenecks would have occurred
during founding events or during periods of range contraction in southern
refugia. Southern refugia, situated within the mid-latitude belt, were vital
to the persistence of temperate Eurasian hominds.
(7) The robust Neanderthal and early Modern Human morphology is typical
of middle Pleistocene hominids (Trinkaus & Rhoads, 1999). It re¬‚ects
the continuing adaptation to the exploitation of mammalian herbivores
in intermediate habitats and landscapes over heterogeneous terrain. Any
attributable climatic advantage of the Neanderthal robust morphology
(Pearson, 2000) must, in my view, be secondary. The gracilisation of
Moderns re¬‚ects adaptation to more open environments over more homo-
geneous terrain and a change in hunting strategies with increased use of
long-range projectiles. Humans have become increasingly re¬ned
risk managers. With increasing environmental variability, genetically-
determined behavioural plasticity has been selected. In the rapidly chang-
ing world of the late Pleistocene, behavioural ¬‚exibility has been the
mechanism that has permitted immediate response to abrupt environmen-
tal changes. This is the subject of Chapter 5.
5 Comparative behaviour and ecology
of Neanderthals and Modern Humans

An understanding of the ecology of any species must include a knowledge of
what it eats, where it ¬nds it (and also water) and how it catches and pro-
cesses it, where, when and with whom it breeds, where it obtains shelter and
how it avoids predation and competition. These are problems common to all
animals and need to be examined at different scales in order to fully compre-
hend them: daily, seasonal and inter-annual cycles may all have a bearing on a
population™s survival. Similarly, the spatial scale of operation of individuals (ter-
ritories/habitats), groups (home ranges/landscapes), metapopulations (regions)
and the species as a whole (geographical range) are critical in understanding its
ecology. It follows that the patterns we may observe may be heavily dependent
on the scale at which we observe them. In the case of humans one thing that will
emerge throughout is that there are problems associated with generalisation at
small scales. The world of Pleistocene humans, especially Neanderthals, has
to be seen as a spatio-temporal mosaic at the scale of human generations. This
makes it very dif¬cult, as we will see, to establish generalised hypotheses other
than at the large-scale, ultimate, levels of causality. I will now examine aspects
of Neanderthal and Modern Human ecology from the perspective of resource
acquisition with the view of comparing and contrasting the two forms.



Food and feeding ecology

Any comprehensive theory of hominid evolution must rest heavily on a theory
of resource acquisition (Kaplan & Hill, 1992). In the speci¬c case of the Nean-
derthals and early Moderns an understanding of foraging strategies is critical
(Marean & Kim, 1998). The initial success of hominids in exploiting open sa-
vannah environments may lie partly in the spatio-temporal mapping memory
of ancestral tropical forest frugivores (Milton, 1981). After 2 Myr a cooler and
drier, and more seasonal climate made fruit a less dependable source of food.
There was therefore a shift to underground foods such as tubers, which are
relatively abundant in the savannahs. Speth (1989, 1991) considered that there
were physiological limits to total protein intake and that meat consumption
was therefore kept at moderate levels by early hominids. Bunn & Ezzo (1993)

94
Comparative behaviour and ecology 95

considered the importance of roots and tubers as ef¬cient stores of nutrient
and water with the added advantage of availability over most of the year and
resistance to ¬re and drought. These would also have been easy to collect and
so they may have been of some importance in the ancient hominid diet.
Nevertheless, where forests gave way to savannahs at the end of the Pliocene
in East Africa, carbohydrates may have become the limiting nutrient in early
hominid environments, requiring compensation through higher intakes of pro-
tein and fat (Bunn & Ezzo, 1993). Metabolic adaptation to long-term intakes of
high levels of protein is experimentally demonstrable. In any case there is clear
evidence of large-scale meat processing as from 2 Myr (Walker, 1981) which
increased signi¬cantly with archaic sapiens forms, especially the Neanderthals
(Foley, 1992). Foley (1989) relates the appearance of Moderns to increased
foraging ef¬ciency and the utilisation of animal resources. The use of meat
appears to have evolved as a mechanism for enhancing ¬‚exibility for coping
with periodic uncertainties in the food supply, given that in tropical savannah
systems a range of mammals in a wide state of physical conditions would have
guaranteed year-round availability, and provided critical nutrients and energy
(Bunn & Ezzo, 1993). Muscle meat is, in particular, a valuable energy source
and an important store of food that might sustain for considerable time periods
a population accustomed to irregular feedings and unpredictable food resources
(Bunn & Ezzo, 1993).
The response to spatio-temporal variability by hunter“gatherers is resolved
by averaging out over time and space. Fat deposition, storage and other cultural
buffers (e.g. food sharing, Kaplan & Hill, 1985) can do this. Trade can replace
mobility as a way of averaging over spatial variation when increased competition
requires greater productivity (Cashdan, 1992). A greater reliance on storage is
associated with a decrease in mobility (Binford, 1980). Other authors consider

<<

. 16
( 43 .)



>>