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presence of leopard spotting amongst Botai horses implies
a degree
of human selection and husbandry. The selection may have been
intentional to increase the number with a desirable coat colour, but
husbandry might equally have removed causes for negative selection
normally seen in the wild.
Secondly, horse demographic profiles, in terms of changing
effective populations, can be modelled over time from levels of
genetic drift. Such a Bayesian demographic
profile for horses shows
a strongly negative trajectory from the last glacial maximum into the
early Holocene, something that only reverses again after the spread
of domestic horses in the last 5,000 years. The horse went extinct in
North America, whilst in Eurasia it appears populations were also in
severe decline and becoming more fragmented. Having been mixed
hunter-gatherers through the Mesolithic and Neolithic, it seems
almost inconceivable that, faced with plummeting horse populations,
they would suddenly focus all their effort on hunting just that species
whilst simultaneously becoming less mobile and settling in large
villages. On the other hand, if their reaction to the problem was to
domesticate the animal,
breed it and control it, then this sudden
change of lifestyle makes sense. However, having added yet more
strong lines of evidence that Botai horses were domestic, this new
work also shows that Botai horses were not the main genetic source
for modern domestic horse stock. One obvious implication would be
that there is a second, and more successful, centre for early horse
domestication, and that second clade comes to dominate with only a
limited amount of Botai admixture surviving by the Iron Age.
In addition to having whole genomes for Botai horses we now
also have three whole genomes for Botai humans, and indeed a
series
of other Eneolithic and Early Bronze Age peoples of the northern
Central Asian steppe. These results are also surprising and
significant. They show that the people of this region at this time were
effectively a very late relict population that had changed very little
over the thousands of years since the Palaeolithic and showed little
sign of admixture from outside. There are a series of significant
implications to this, but in relation to
Botai it tells us something about the possible circumstances of
horse domestication in that culture. Zeder (2012) laid out a number
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of pathways to animal domestication: ‘commensal’, ‘prey’ and
‘direct’. Commensal is where an unintended close living association
might eventual change into domesticity, with the dog being an oft
cited example of this. Prey route is where the relationship with a
common quarry changes over time (again potentially unintentionally)
to involve more and more control. This is the most common form of
domestication relating to food animals and one most frequently
undertaken by peoples who were already plant agriculturalists, but
still hunted animals. Directed pathway domestication
implies a prior
knowledge of what it is to domesticate an animal and the deliberate
act of targeting a species to do that. Zeder cites horse as an example
of the rare direct pathway and thus suggests that, as a relatively late
example of a major domesticate, it was targeted by people with
knowledge of the process themselves or through interaction with
others, as suggested by Anthony and Brown (2011). However, in the
specific case of the Botai, the genetics implies continuity of local
hunter-gatherer populations with no evidence for outside contact that
left any genetic mark. As such this would imply a prey route
domestication by local hunter-gatherer populations. This is actually
quite rare and its only clear parallel is reindeer domestication.
Reindeer are also animals that were hunted by relict Palaeolithic-
derived populations, but can also be ridden and milked. Indeed the
close cosmological parallels between reindeer herders and hunters
have been noted. One can envisage a very similar process at Botai by
hunter-gatherers
with similar ancestry, relating to animals that can
perform similar functions. Whilst reindeer are common to the taiga,
horses are common to the more southerly forest steppes. It now
seems, when considering the human and horse ancient genomic data
together, that there was a significant population replacement, dating
to the middle Bronze Age, that saw peoples like the Botai and their
local horse stock, eventually replaced by groups migrating from the
West with their own horse.
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