<<

. 7
( 43 .)



>>

VO
n




AE
ae

o
D



R
p




I




Figure 2.4. Comparison of mean (with 95% con¬dence limits) number of major
mammalian herbivore species in African localities with hominids and without
hominids (after Bromage & Schrenk, 1999). Arrowheads point to taxa in which
statistically signi¬cant differences are found with more species in sites associated with
hominids than in those without.




(1) Rocky habitats that usually hold small- to medium-sized mammalian her-
bivores. The Eurasian mid-latitude belt appears particularly favourable
throughout with, for example, ibexes Capra spp. and chamois Rucicapra
sp. Some Capra have penetrated as far as the north-eastern coast of Africa.
The klipspringer Oreotragus sp. in Africa and the mountain goat Oream-
nos sp. in North America, occupy similar habitat.
(2) Wetlands would have acted as focal, usually seasonal, points of concen-
tration of mammalian herbivores as well as other animals (e.g. wildfowl,
reptiles, amphibians, ¬sh). The species range present in each site would
be dependent on geographical location and surrounding habitat. In gen-
eral terms, the species typical of open landscapes would be expected.
Hippopotamus Hippopotamus sp. would have been a mammalian herbi-
vore typically associated with such habitats in warm areas.
Biogeographical patterns 35

(3) Coastal habitats would have attracted a particular group of animals. It is
becoming increasingly apparent that hominids regularly exploited such
habitats in different parts of the world (Klein, 1999; Stiner, 1994, Fin-
layson et al., 2000b). Marine mammals may have been largely acquired
by scavenging but there are indications that suggest that seals may have
been selectively harvested at particular times of the year (Balter, 2001).
Harvesting marine mammals by hominids may have been localised or
may have been a more generalised habit. In addition to marine mam-
mals, molluscs were harvested in a number of coastal regions, for ex-
ample in the Mediterranean and Atlantic (Stiner, 1994; Finlayson et al.,
2000b).


Mammalian herbivore biogeographical patterns and climate

Climate change would have been largely responsible, through habitat change,
for modi¬cations in the distribution patterns of mammalian herbivores. These
would have largely taken the form of expansions, contractions or shifts in the
range of each species in response to their particular requirements (FAUNMAP,
1996). The similarity of requirements of a number of species, or their inter-
dependence, would produce patterns of apparent movements of faunas as is
often reported in the literature (Tchernov 1992, 1998) but this would be no
more than coincidence in response to the same ecological parameters. At other
times, species™ responses would have varied and the effects on geographical
distribution would also have been different, thus producing apparently unusual
combinations of species in particular areas. The intensity and range of such
responses would have in addition varied depending on the particular history
of each population. Thus, two populations of the same species might show a
different level of response to the same signal at different times because of such
variations as starting population size or geographical range centre. It is for these
reasons that animal communities can be so different through time and why past
communities may have no present-day analogues (Guthrie, 1984). The possible
combinations are virtually in¬nite.
Despite these dif¬culties it is possible to establish certain patterns. At the
higher taxonomic levels (such as family and sub-family) the distribution of,
for example, mammalian herbivores is fairly constant in spite of large climatic
and environmental ¬‚uctuations (Table 2.1; Figure 2.3). There are, for example,
elephants across much of Eurasia, Africa and North America throughout, so
hominids would encounter this herbivore type in suitable habitats across much
of their range. The same would apply to the other herbivore resource types
discussed earlier in this chapter “ i.e. rhinoceros, large bovid, horse, medium
36 Neanderthals and Modern Humans

bovid/deer, small bovid/deer and pig. The exceptions would have been the ice,
sandy and stony deserts. As these deserts retreated under particular climatic
circumstances (Chapter 6), higher order herbivore types that had been absent
would have had the opportunity to enter. This would have occurred, for example,
when tropical African mammals occupied areas of the Sahara or when Eurasian
Plains herbivores colonised boreal regions.
The responses (range changes or extinctions) to climatic and environmen-
tal ¬‚uctuations would therefore have been more frequent at lower taxonomic
levels and detectable at the species and, less frequently, the generic levels. The
responses would be even more frequent, but more dif¬cult to detect, in local
populations of a species. In the case of mammalian herbivores such changes
could also have had an impact on predators, including hominids, in cases where
different species had different behaviours. In terms of the strategies required to
exploit them, the migratory reindeer of the plains were a very different resource
from the red deer of the woodlands. So, for example, although medium-sized
deer would have been available to hominids in southern France for much of the
Middle and Upper Pleistocene, the actual species present would have varied
considerably depending on climate-induced habitat changes (Mellars, 1996). I
will discuss the impacts of such changes on hominids at the level of species and
populations in Chapter 5.
Main trends in mammalian herbivore range shifts that would have been sig-
ni¬cant to hominids at the macro-ecological level would have been:


(1) The north“south range changes of tropical savannah and grassland African
species in relation to the expansion and contraction of the Sahara.
(2) The north“south range changes in Arctic species in relation to the expan-
sion and contraction of the glacial ice sheets and the tundra.
(3) The east“west range changes of steppe-adapted species across the Eurasian
Plain in relation to the expansion and contraction of the steppe.
(4) The range contractions and expansions of tropical savannah and grassland
species in Africa, South and South-east Asia in relation to the expansion
and contraction of the rainforest.
(5) The north“south range contractions and expansions of temperate species
into and out of mid-latitude refugia in relation to changes in the distribution
of forest and shrublands.
(6) At a smaller spatial scale, the altitudinal shifts in the distribution of species
in topographically heterogeneous landscapes in response to temperature
controlled vegetation changes.
Biogeographical patterns 37

Synthesis

We may therefore identify the following trends that will assist us in our synthesis
of human evolution in the following chapters.

Mammalian herbivores as a resource

The medium-sized (100“1000 kg) packages of protein that were consumed by
humans during the Pleistocene were available world-wide and throughout the
Pleistocene. Minor differences in taxa separated the regions. The constancy in
availability of these packages permitted humans to adapt for their exploitation.
The robusticity of many human populations re¬‚ects such adaptation to hunting
these mammalian herbivores. The loss of mammalian herbivore diversity and
biomass at the end of the Pleistocene led to the herding and domestication of
certain species, in particular the goat, sheep, cattle, pig and horse (Diamond,
1997). This may be considered as a latter form of adapting to this resource.

Topography of the terrain as a template in which to obtain
mammalian herbivores

The topography of the terrain at large scales has been another constant through-
out the Quaternary. Humans, depending on where they settled, were therefore
able to adapt to the types of terrain in which they were able to make a living.
Those in Africa adapted to a mix of ¬‚at and broken landscapes. As they ex-
panded away from Africa they would have adapted further to the speci¬cities of
the terrain colonised. Those reaching the mid-latitude belt increasingly adapted
to broken terrain while those, much later, reaching the plains of Eurasia would
have increasingly adapted to ¬‚at landscapes. In either case, and also in terms
of ability to obtain mammalian herbivores, existing African templates would
have pre-adapted humans to ex-African colonisations.

Habitats and landscapes

The distribution of landscapes and habitats changed frequently during the Qua-
ternary in response to climate change. The rate of change intensi¬ed through
the Pleistocene. Humans were initially adapted to intermediate habitats (those
between closed forest and open plains) and mosaic landscapes. Through time
they increasingly adapted to open habitats and plains landscapes. Adaptation to
intermediate and then open habitats and landscapes enabled range expansions
38 Neanderthals and Modern Humans

in humans. Because habitats and landscapes frequently changed spatial loca-
tion due to climate changes, humans instead of adapting in situ tracked these
changes. This tracking across spatio-temporal scales marked the range expan-
sions, shifts and contractions that I will describe in Chapter 3.


Barriers

Desert and sea, in particular, acted as physical and ecological barriers to range
expansion or shift. Their extent, from total impermeability to high porosity,
varied with climate change. Cold and aridity intensi¬ed desert barriers but
reduced marine barriers. Some, like the deep Strait of Gibraltar, were barriers
throughout. Barriers can also occur at smaller spatial scales, as between habitat
patches, the scale of an individual™s perception of the environment being critical
in the ability to overcome such barriers (Wiens, 1997).
Tropical“boreal gradients characterised human evolution and acted as bar-
riers that were progressively dismantled. Throughout the Quaternary, tropical
environments have provided greater resource diversity than boreal ones. Hu-
man resource consumption is therefore expected always to present a pro¬le of
decreasing diversity from the tropics towards higher latitudes. Temperate envi-
ronments have occupied an intermediate position. Humans have adapted in the
form of an omnivore“carnivore gradient. Colonisation of boreal environments,
in particular, required almost total carnivory. There is a corresponding daylength
seasonality regime between the tropics and the polar regions. These constants
have been critical in the adaptation of humans to non-tropical environments.
In the following chapters, these trends will allow us to interpret human evo-
lution in the Quaternary. Humans adapted to obtaining mammalian herbivores
in rugged terrain in intermediate habitats and landscapes. In time they also
adapted to resource-rich environments characterised by ¬‚at terrain and open
landscapes. The changes in habitat and landscape modulated the spatial dis-
tribution of populations that were driven by these adaptations to resource and
terrain. Barriers temporarily suspended this dynamic system.
3 Human range expansions,
contractions and extinctions

African beginnings

We saw in the previous chapter how climate-induced habitat and landscape
changes acted as catalysts to human range expansions, shifts and contractions.
This chapter explores these processes in greater detail.
Novelty in the genus Homo was generated repeatedly in eastern Africa. It is
not unexpected that the sources of biological novelty should be tropical given
the tropical nature of the primates as a whole (Foley, 1987) and the scarcity
of species that reach away from the tropics. The nature of the distribution of
the ape lineage and the distribution of open savannah-type habitats close to
tropical forest make an African tropical origin a virtual certainty and this is
well supported by the fossil evidence (Stringer & Gamble, 1993; Akazawa,
1996a; Klein, 1999). Novelties arose repeatedly in the Homo lineage but they
also occurred deeper in time with the adaptations to open environments and
departures from frugivory and herbivory of the pre-Homo forms.
Arid communities became established in East Africa by 23 Myr and there
has been no real change in vegetation in the past 15.5 Myr. C4 vegetation, char-
acterised by grasses and sedges in warm arid, open, habitats, appeared around
15.3 Myr bp (Kingston et al., 1994). Early hominid evolution took place in
sub-Saharan Africa in situations of increasing environmental instability that
led to forest contraction and at the expense of open environments (Foley, 1987;
Foley & Lee, 1989; Bobe et al., 2002). Early hominid evolution took place
within the context of a heterogeneous mosaic of environments in intermediate
situations between the closed forest and the open grasslands (Kingston et al.,
1994). Tropical climate was cool and variable during glacial cycles (Schrag
et al., 1996; Thompson et al., 1997; Webb et al., 1997; Bush & Philander,
1998). These effects, generated by the expansion of the high latitude ice sheets,
were met, especially in the last 1 Myr, by abrupt vegetation distribution changes
largely caused by increased aridity (deMenocal, 1995; Hughen et al., 1996).
These changes led to the progressive expansion of open vegetation that be-
came central to human evolution. Occupation of open habitats required abili-
ties for coping with increasing uncertainty, seasonality and patchiness. These
needs were met by morphological and behavioural responses (Foley, 1992;


39
40 Neanderthals and Modern Humans

deMenocal, 1995; Stanford, 1999; Stanford & Bunn, 2001). The advantage of
these open environments centred around their high net primary productivity
(Field et al., 1998) and the relative ease of locating aggregations of mammalian
herbivores.
Evolution in the genus Homo is marked by a series of adaptations that im-
proved performance in the arid and open terrestrial environments of Africa,
and conditioned the course of that evolution (Foley, 1987, 1992; Foley &
Lee, 1989). Beginning with bipedality (Jablonski & Chaplin, 1993; Hunt,
1994, Isbell & Young, 1996; Richmond et al., 2001), these adaptations were
morphological and behavioural, including in its most sophisticated form, cul-
ture (Wheeler, 1994, 1996; Queiroz do Amaral, 1996; McHenry & Berger,
1998). Brain enlargement, reaching a maximum in the archaic humans (e.g. the
Neanderthals) and in the Modern Humans, stands out among these adaptations
(Aiello & Dean, 1990; McHenry, 1994; Aiello & Wheeler, 1995; Kappelman,
1996; Elton et al., 2001). We can attribute these adaptations to increasing spe-
cialisation to the open and arid environments of tropical Africa (Reed, 1997)
and they improved resource acquisition and, incidentally, permitted expansion
outside Africa. Such features included increased body size and a long-limbed
morphology that enabled changes in ecology, including larger home ranges and
increased dispersal ability (Anton et al., 2002) and the capacity for endurance
running (Carrier, 1984). They pre-adapted populations for success in other open
environments, reaching the maximal expression in the late Pleistocene on the
Eurasian Plain (Gamble, 1986, 1993, 1999).

<<

. 7
( 43 .)



>>