Author : Wahid Ahmad
Dogs were
our earliest companions during the prehistoric era. Ancient DNA studies reveal
the intertwined journey of humans to the Americas and their loyal canine
friends, offering a glimpse into the fascinating partnership.
Studies indicate that dogs are closely linked to the movements of human groups
over time and across different regions. For example, when farmers migrated from
West Asia to Europe, a particular group of dogs with a specific mitochondrial
haplogroup accompanied them.
The first dogs in New Zealand arrived with Polynesians, and in the North
American Arctic, dogs with a unique mitochondrial DNA signature joined
Paleo-Inuit groups around 5,000 years ago. Later, when Inuit groups moved into
the same region about 1,000 years ago, a new population of dogs with different
DNA signatures appeared.
These connections between human migrations and specific dog lineages likely
began soon after dogs were domesticated from Eurasian grey wolves. However,
we're unsure about the exact time and location of this domestication process.
Domestication of Dogs
Scientists
are trying to uncover the origins of domestic dogs, the first animals
domesticated during the Pleistocene epoch amidst environmental changes. Studies
suggest the original wolf population that led to dogs is extinct. Dog
domestication likely occurred in Eurasia, but many details remain unclear.
Despite using genetics and archaeological evidence, the timeline and specifics
of dog domestication are still debated. Identifying early domestic dogs from
wolves is challenging, as common markers like tooth crowding and skull size
often don't provide clear distinctions. Disputes arise over claims of early
domestic dogs at certain sites due to difficulties in differentiation from
wolves.
The site of Bonn-Oberkassel in Germany stands out as the earliest generally
accepted remains of a domestic dog, dating back to approximately 15,000 years
ago. The distinct morphology and genetics of this young dog set it apart from
local wolves. Additional potential domestic dogs have been suggested at various
Pleistocene sites, including some in Siberia and the Americas are still under
investigation.
Divergence of Dog lineages
Scientists have studied the DNA of many ancient and modern dogs. The analysis
of nuclear DNA shows that all dogs come from three main groups of ancestors:
one from Western Eurasia (mostly in Europe, India, and Africa), one from East
Asia (like dingoes), and one from the Arctic (like huskies and ancient American
dogs). These lineages were established at least 11,000 years ago.
When looking at mitochondrial DNA, most modern dogs fall into four main groups
called haplogroups A, B, C, and D. The majority belong to haplogroup A. Ancient
DNA studies found a unique haplogroup A2B in pre-contact dogs in the Americas
south of the Arctic, but it has almost disappeared in modern dogs.
Within A2 B, there are four subgroups A2 B1 to A2 B4, while A2 B1 is found all
across the Americas, the others are more localized.
Scientists used molecular clock analysis to estimate when these haplogroups
split. The oldest split within haplogroup A, between lineages A1B and A2, is
estimated to be around 22,800 years ago. This suggests that dogs were
domesticated several thousand years before they appeared in the archaeological
record. This early timeline suggests that dogs were likely domesticated by the
time humans migrated into the Americas.
Peopling
of Americas
Researchers have traced Native American ancestry
back to a population that diverged from an East Asian ancestor around 30,000
years ago. Around 24,000 years ago, this population split into two groups:
Ancient Paleosiberians in northeast Asia and the basal branch of Native
Americans.
At approximately 24,000 years ago, both groups received gene flow from Ancient
North Siberians. During the Last Glacial Maximum around 23,000 to 19,000 years
ago, the basal branch of Native Americans underwent a period of isolation in
northeast Asia known as the Beringian Standstill, lasting possibly 2,400 to
9,000 years.
Around 21,000 years ago, the basal branch split into Ancient Beringians and
Ancestral Native Americans. Both populations entered eastern Beringia
(present-day Alaska), with the Ancient Beringians not showing genomic evidence
south of Alaska after around 9,000 years ago. The Ancestral Native Americans
diversified around 15,700 years ago into northern and southern branches.
The split between northern and southern branches occurred as the Ancestral
Native Americans moved south from Alaska, suggesting a route along the Pacific
coast rather than the interior "ice-free corridor," which wasn't yet
suitable for human foragers. The estimated time of this split aligns with
archaeological evidence of people in the Americas around 15,000 years ago,
supporting the idea of a Pacific coastal route.
It's important to note that the actual arrival date in the Americas remains
unclear, as archaeological evidence provides a minimum age, and genetic
estimates offer a maximum value. Once south of the ice sheets, the northern
branch had a limited geographic spread, while the southern branch radiated
throughout the hemisphere, diverging genetically around 14,100 years ago.
Dual Dispersal into Americas: Dogs and Humans
The relationship between the migration of humans
and dogs into the Americas during the late Pleistocene period is fascinating.
It suggests that dogs may have accompanied the first people entering the
Americas and explores the timeline of their divergence.
The Americas were settled by humans relatively late, and it's possible that
when people first arrived, they had dogs with them. Dogs could have played a
role in helping humans quickly spread throughout the region. Comparing the
timelines of dog and human populations, researchers found key points of
convergence.
The introduction of dogs in the Americas is estimated using mitochondrial data,
and it aligns with the timing of human population splits. Ancient American
dogs, excluding the Arctic, belong to the same lineage (A2b), suggesting they
coalesced with a Siberian dog lineage around 16.4 thousand years ago. This
timeframe coincides with the peopling of the Americas.
The evidence indicates that dogs likely crossed the Beringia land bridge during
the Pleistocene, reaching the Americas before later human migrations. The split
between major Native American lineages aligns with the divergence of dog
lineages, suggesting they evolved together.
While both Ancestral Native Americans and Ancient Beringians groups could have
brought dogs into the Americas, archaeological evidence hints that Ancestral
Native Americans might have been the first, arriving before the distinctive
Ancient Beringians group. This suggests a connection between the migration of
people and dogs into the Americas during this period.
Ancient DNA suggests that dog domestication likely began in Siberia during the
Late Pleistocene, a period around 26,000 to 19,700 years ago. This aligns with
the time when humans and their genetically divergent groups were present in
Siberia and western Beringia. The evidence indicates that human populations in
this region were small and lived in relative isolation.
The lack of significant gene flow among these groups and the absence of
archaeological sites suggest limited interaction with communities outside
Siberia. As these populations, specifically the ancestors of Native Americans,
crossed into the Americas, they brought dogs with them. The question arises:
How did Ancestral Native Americans acquire dogs? The researchers propose that
dogs were likely domesticated from a wolf population in Siberia or western
Beringia during the Late Pleistocene before Ancestral Native Americans migrated
into the Americas.
Among the various groups present in Siberia during the Last Glacial Maximum,
the researchers eliminate some possibilities and suggest that the Ancient North
Siberians are the more likely population to have initiated the domestication
process. Genomic analyses of ANS individuals at Siberian sites show evidence of
gene flow into both ancient Native American and Western Eurasian lineages.
This suggests a mechanism for the transfer of dogs into different groups,
supporting their movement both east and west following domestication. The
researchers propose that climatic conditions during the Last Glacial Maximum
brought human and wolf populations into proximity within refugial areas,
leading to increased interactions. Mutual scavenging of kills or wolves drawn
to human campsites may have initiated a shift in the relationship between
humans and wolves, eventually resulting in dog domestication.
The evolving relationship between humans and dogs has played a crucial role in
their successful global spread, with more insights expected as archaeological
and scientific techniques advance.