The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 181

In Europe Neanderthals ( H .) evolved from 300 000 years ago (or about three gla-
cials ago), although DNA analysis suggests their genetic divergence from a common
ancestral stock some 600 000 years ago. Archaic Neanderthal remains have been
found in Spain dating from somewhere between 530 000 and 250 000 years ago and
there is some suggestion that this could have been a core Neanderthal population for
western Europe; western European Neanderthals could certainly have outridden gla-
cials there. Although competition with modern humans undoubtedly pressurised the
Neanderthals, there is radiocarbon dating evidence from southern Spain that climate
change contributed to their final demise around 24 000 years ago, as that was the time
of a Heinrich event (see section 4.5.3) and its associated northern hemisphere climate
fluctuation (Tzedakis et al., 2007).
Neanderthals had some DNA sequences not found in H. sapiens .Havingsaid
that, there is genetic evidence that H. neanderthalensis did breed with H. sapi-
ens in the Middle East and Europe sometime around 90 000-65 000 years ago (the
more recent date fits other evidence), as well as in the Far East around 50 000-
40 000 years ago (see a review by Callaway, 2011, along with other references in this
section).
There was a H. sapiens population bottleneck with a reduced population of about
10 000 individuals in Africa during the Pleistocene. There is some debate as to what
caused this bottleneck and speculation includes global environmental change due to
a super volcano, possibly the eruption of Toba 74 000 years ago, which is thought to
have lowered temperatures by 3-5 ◦ C for up to 5 years (see section 6.6.5). It may be
that it was due to the combination of a glacial and these factors, or even another factor
entirely. In 2011, genetic comparison of 21st-century humans (a Chinese, a Korean,
three Europeans and two Yorbas) was conducted by Heng Li and Richard Durbin of
the Wellcome Trust Sanger Institute in Cambridge, UK. Put briefly and simply, the
larger a population is the more genetic diversity it can have. Due to mutation and other
processes, genetic sequences change over time, from generation to generation. Put
these two together and (admittedly making assumptions about the rate of change) it
is possible to get a very rough and ready history of a population's size over time. This
can be even more rough and ready if you are working with a small number of people
(genomes), which Heng Li and Richard Durbin were. Yet they were able to loosely
detect a bottleneck in the human population somewhere around 60 000 years ago.
Furthermore, they estimated the populations of European and Asian humans to have
been of a similar size before 20 000-10 000 years ago, with a far greater constricted
population than that of the African humans. The African population bottleneck seems
to have been smaller and to have recovered quicker. Could this be the genetic echo
of the Toba eruption 74 000 years ago? Toba is in Indonesia and would have had
a bigger impact on any human population in Asia than Africa. In addition, the
higher-latitude European population would have been more susceptible to a sudden
cooling of the climate for a few years following such an eruption than those in
warmer Africa.
Anyway, subsequently this African population expanded some 100 000-50 000
years ago, during which some left Africa and then, somewhere around 95 000-65 000
years ago (in the last glacial) there was an expansion in Europe, where H. sapiens met