Sydney, Nov 14 (The Conversation) From village dogs to toy poodles to mastiffs, dogs come in an astonishing array of shapes, colours and sizes. Today there are estimated to be about 700 million dogs living
with or around humans.
To many of us, dogs are loyal companions, working partners, and beloved family members – and the histories of our species are deeply woven together. But how did this incredible diversity come to be – and how far back does this relationship with humans go?
Two new studies published today in Science provide some answers. One, led by Allowen Evin from the University of Montpelier, draws on ancient skeletal remains. The other, led by Shao-Jie Zhang from the Kunming Institute of Zoology, draws on the study of DNA from ancient Eastern Eurasian dogs.
Together, these studies suggest the story of dogs and their relationship with humans is older and more complex than once thought.
The origins of modern dog diversity
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The study by Evin and her colleagues used 643 dog and wolf skulls spanning the past 50,000 years to address the origins of modern dog diversity.
Her team’s analysis suggests the distinctive “dog-like” skull shape first arose around 11,000 years ago, during the Holocene epoch, the time since the most recent ice age. They also found substantial physical diversity in dog skulls from the same period.
This means the wide range of shapes and sizes dogs have today isn’t solely a product of the intense selective breeding programs that became popular in the last few centuries. Some of that variation emerged millennia earlier.
The team re-analysed the skull shapes of all 17 known dog or wolf skulls from the Late Pleistocene, a geological period from 129,000 to 11,700 years ago. Some skulls were 50,000 years old.
They found all of these Pleistocene skulls were essentially wolf-like in shape, including some previously identified as early dogs.
Importantly, this suggests that while the split between wolves and dogs likely occurred during the Pleistocene, the skull shape of early dogs didn’t start to change until closer to the Holocene – that is, 11,000 years ago. However, some Holocene dog skulls still retained wolf-like features.
This research suggests early dogs were much more diverse than previously thought. This diversity may have laid the groundwork for the extreme variations in size and shape of the dogs we have today.
Travelling companions
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Earlier genomic studies have uncovered four major dog lineages that likely originated about 20,000 years ago: Eastern (East Asian and Arctic) and Western (Europe and Near East) dogs.
The origins of these ancient dog lineages are still being untangled. However, studying shifts in the ancestry of dogs through time and between different regions can help us better understand both the origins of dogs and the movement of Neolithic (new stone-age) humans.
The new study by Zhang and his colleagues used 73 ancient dog genomes spanning the last 10,000 years to explore how humans and dogs moved across Eastern Eurasia through time.
Analysis of these ancient dogs identified multiple shifts in the ancestry of dogs in Eastern Eurasia at times that correlate with the movement of specific human groups (hunter-gatherers, farmers and pastoralists). This suggests that as different human cultural groups moved across Eurasia, their dogs often moved with them, carrying their unique genetic signatures.
There was some discrepancy between human and dog population ancestry in some parts of Asia. For example, Eastern hunter-gatherers from Veretye and Botai, who were more closely related to Western Eurasian humans, had largely Eastern (Arctic) dogs rather than the Western dogs observed with other Western Eurasian cultures at the time.
This means dogs may have been a key part of cultural exchange or trade between different human cultures or communities. It may also illustrate complexities in the evolution of dogs that we are yet to understand.
The work by Zhang and his team presents compelling evidence that in Eastern Eurasia thousands of years ago dogs played an indispensable role in human societies as crucial “biocultural packages” that moved with humans. In other words, humans took their companions with them on their journeys (and perhaps traded them), rather than simply acquiring new dogs after moving.
These findings highlight the long-term, complex and intertwined relationship between dogs and humans that spans more than 10,000 years.
The genetic ancestry of dogs can act as a living record of ancient human migrations, trade networks and cultural exchanges. Studies on ancient dogs may also help us understand the environmental factors that contributed to the evolution of dogs, and their relationship with humans.
Reshaping our understanding of dogs
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Together, these new studies profoundly reshape our understanding of how dogs became so diverse and how they have related to humans along the way.
Both studies underscore that the incredible diversity in modern dogs is not an entirely recent phenomenon. The genetic and morphological foundations for this variation were laid thousands of years ago, shaped by natural selection, human selection and diverse environments, long before the structured breeding of the past few centuries.
Future studies investigating the physical diversity and ancestry of dogs through time could deepen our understanding of the complex origins and spread of dogs across the globe. Whatever their origins, this research deepens our appreciation for the unique and ancient bond between humans and dogs that was almost as diverse as canines themselves. (The Conversation) RD
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