The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 167

varies but both these species went extinct around the start of the Holocene. Of course,
not all megafauna became extinct: reindeer currently remain relatively unaffected
by either of these factors. This study could not elucidate the causes underlying the
extinction of woolly mammoth but it is hard not to conclude that humans did play a
part, given that mammoths survived previous interglacials and their demise in some
places does seem suspiciously concurrent with the arrival of humans.
It is interesting to note that the late Pleistocene and early Holocene extinctions
were largely driven by a combination of both climate change and human pressure,
for today's current extinctions are similarly driven. The only difference between
these two extinction periods is that the late Pleistocene and early Holocene extinction
was partly driven by natural climate change whereas the current extinction involves
anthropogenic climate change. It is also interesting to note that the degree of extinc-
tions on each continent varied depending on the length of human existence (see Table
4.1). Because humans evolved in Africa, and then spread to Eurasia, animals here had
a chance to co-evolve. (We shall shortly return to this in the next section on biological
response.)
Taking all the evidence together, what seems to be happening with regards to human
and climate impact on megafauna? First, we need to note that megafauna had survived
the comparable climate change that took place at the ends of previous glacials. The
only substantially different factor at the end of the last glacial and beginning of this
(the Holocene) interglacial was the presence of humans. This suggests that humans
were involved in the megafauna extinctions that took place. That the considerable
global climate change of the LGM-Holocene has been a factor in species demise is not
surprising. As Lorenzen et al. (2011) point out, a species' response, or sensitivity, to
this climate change varies with the species so it seems likely that those more sensitive
to climate factors were more prone to impact from humans. The size of megafaunal
populations do seem to have been in decline during the LGM-Holocene transition
( 20 000-10 000 years ago). A number of the megafaunal extinctions appear to

have taken place around the start of the Holocene, 12 000-10 000 years ago. But
remember that there are problems with dating accuracy. It could be that the false end
of the last glacial at 14 000 years ago, with the brief (Younger Dryas) abrupt return
to part-way more glacial conditions (Figure 4.12), could have provided additional
climate stress that made species more vulnerable to human impact. (Remember that
the Younger Dryas was more pronounced in the northern hemisphere where the
Palaeolithic megafauna extinctions took place.) The conclusion by Lorenzen et al.
that 'no evidence that Palaeolithic humans greatly impacted musk ox populations'
is at first curious as the musk ox survived well into the Holocene until just a few
hundred years ago and during all this Holocene time (

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10 000 years) the climate was
stable. Their conclusion seems to be based on 'Musk ox remains [being] found in
only 1% of European archaeological sites and 6% of Siberian sites, and do not overlap
noticeably in range with Palaeolithic humans in either Europe or Siberia'. True, musk
ox populations seem to have declined in the Palaeolithic and this may well be because
their habitat is one of a very cold climate. However, the musk ox would have certainly
encountered humans after the Palaeolithic and been particularly vulnerable to human
impact having a low population and reduced area of habitat at that time. All in all,

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