Brains, Brawn or Both: What Drove the Creation of
Modern Dog Breeds?
Genetic variants associated with brain development
help distinguish breeds designed for different physical tasks, a new study
reports.
Sheep herding breeds appear to have a high number of
genetic variants associated with a neurodevelopmental process known as axon
guidance, which ensures that neurons are wired together correctly.
By Emily
Anthes
Dec. 8,
2022
In creating
modern dog breeds, humans sculpted canines into physical specimens perfectly
suited for a wide variety of tasks. Bernese mountain dogs have solid, muscular
bodies capable of pulling heavy loads, while greyhounds have lean, aerodynamic
frames, ideal for chasing down deer. The compact Jack Russell terrier can
easily shimmy into fox or badger dens.
Now, a
large study, published in Cell on Thursday, suggests that behavior, not just
appearance, has helped qualify these dogs for their jobs. Breeds that were
created for similar roles — whether rounding up sheep or flushing birds into
the air — tend to cluster into distinct genetic lineages, which can be
characterized by different combinations of behavioral tendencies, the
researchers found.
“Much of
modern breeding has been focused predominantly on what dogs look like,” Evan
MacLean, an expert on canine cognition at the University of Arizona who was not
involved in the study, said in an email. But, he emphasized, “Long before we
were breeding dogs for their appearances, we were breeding them for behavioral
traits.”
The study
also found that many of the genetic variants that set these lineages apart from
each other appear to regulate brain development, and many seem to predate
modern breeds. Together, the results suggest that people may have created
today’s stunning assortment of breeds, in part, by harnessing and preserving
desirable behavioral traits that already existed in ancient dogs, the
researchers said.
“Dogs have
fundamentally the same blueprint, but now you’ve got to emphasize certain
things to get particular tasks done,” said Elaine Ostrander, a dog genomics
expert at the National Human Genome Research Institute and the senior author of
the study. “You’re going to tweak a gene up, you’re going to tweak it down.”
In an
email, Bridgett vonHoldt, an evolutionary biologist at Princeton University who
was not involved in the research, called the new paper “a major landmark in the
field of dog genomics and behavior. We know it is complicated. This study not
only gives us hope, it will be viewed as an inspiration for all in the field.”
Still,
major questions remained, some scientists said, including whether humans
deliberately set out to create breeds with specific behavioral tendencies. “We
don’t have a ton of evidence for intentional selection,” said Elinor Karlsson,
an expert in dog genomics at the University of Massachusetts Chan Medical
School who was not involved in the research.
But she
praised the study, noting that the findings were consistent with her own
research, which also concluded that many of the genetic factors that shape the
behaviors of modern dogs originated deep in canine history.
Researchers
analyzed behavioral surveys completed by owners of more than 46,000 purebred
dogs to match behavioral traits with lineages.Credit...Jonno Rattman for The
New York Times
“They’re
really taking advantage of this really complex history of the dog breeds, and
these relatively subtle but real differences in behavior, to explore how
genetics and genetic variation can actually shape these behavioral traits,” she
said.
Behavioral breeding
The
researchers studied the genomes of more than 4,000 canids, including samples
from more than 200 different dog breeds, as well as mixed-breed dogs,
semi-feral village dogs and wild canids, such as wolves and coyotes.
The
scientists used computational tools to map out the genetic trajectories by
which ancient dogs became, for instance, generic herding dogs and then distinct
breeds, like Border collies.
They found
that domestic dogs could be divided into 10 distinct lineages, which generally
included breeds that were developed to perform similar jobs. The terrier
lineage included breeds designed to hunt down vermin, for instance, while the
scent hound lineage included breeds that track game using their sense of smell,
rather than eagle-eyed vision or speed.
Although
some of the lineages do have defining physical characteristics, these features
alone cannot entirely explain this sorting, the researchers noted. “If you look
at the scent hound lineage, dotted throughout there are breeds that have short
legs or long legs or different shapes of tail or different coat colors,” said
Emily Dutrow, a postdoctoral fellow at the National Human Genome Research
Institute and the first author of the study. (The research team also included
James Serpell, an emeritus professor at the University of Pennsylvania School
of Veterinary Medicine.)
To identify
the behavioral traits that best defined each lineage, the researchers analyzed
behavioral surveys completed by the owners of more than 46,000 purebred dogs.
Although
there was plenty of overlap — no single breed has a monopoly on trainability —
in general, breeds created for similar jobs tended to have similar behavioral
traits. And each lineage was characterized by its own pattern of behavioral
tendencies.
For
instance, herding dogs, terriers and scent hounds all displayed relatively high
levels of what is known as “nonsocial fear,” such as fear of loud noises or
strange objects. This predisposition might indicate a heightened sensitivity to
environmental stimuli that could be useful in all three types of canine work,
the researchers say.
Still,
there were differences: Terriers displayed higher levels of predatory chasing
than herding dogs, while herding dogs scored higher on measures of
trainability, the researchers found.
“There is
meaningful behavioral diversification among dogs,” Dr. Dutrow said.
(The scent
hound lineage, alas, scored low on trainability. But that characteristic, the
researchers noted diplomatically, is actually “consistent with selection for
traits advantageous to an independently driven working style focused on
following instincts rather than seeking out human cues.”)
To identify
the genetic underpinnings of these lineage-defining traits, the researchers
conducted a genome wide association study, looking for specific genetic
variants that were unusually common in certain lineages.
The vast
majority of these lineage-associated variants were in stretches of DNA that do
not code forproteins but instead regulate the expression of protein-coding
genes. Many appeared to regulate genes involved in brain development.
“When we
look at the genes involved in the differentiation of dog lineages, a lot of the
action is in genes related to neurodevelopment, suggesting that selection for
cognitive and behavioral features has probably been very important,” Dr.
MacLean said.
For
example, the sheep herding breeds were characterized by genetic variants associated
with a neurodevelopmental process known as axon guidance, which helps ensure
that neurons are wired together correctly. Some of these variants were
specifically associated with genes that have been linked to anxiety and
maternal behaviors, including pup retrieval in mice.
One
hypothesis — still unproven, the scientists note — is that a sheep dog’s drive
to herd is a product of the same anxiety-related neural pathway that motivates
animal mothers to care for their young.
“When you
watch these mice, these mothers gathering up their young, it’s just like
watching a Border collie herd sheep,” Dr. Ostrander said. “And so you could
throw out a hypothesis that maybe that’s the ancestral behavior that’s been
co-opted.”
(Dr.
Ostrander, who used to have a Border collie, has seen this herding drive
firsthand. “I used to be able to bring mine to the lab and she could herd
people up for lab meetings,” she said.)
Still, many
of the variants that were closely associated with specific lineages did occur,
at lower levels, in other lineages or even in gray wolves, suggesting that they
predated the creation of modern breeds.
And just
because there are differences, in aggregate, between canine lineages does not
mean that breed is behavioral destiny, Dr. Karlsson noted.
“That
doesn’t mean that every single retriever is going to retrieve a ball or every
single herder is going to be completely different from every single retriever,”
she said. “Many dogs are not going to fit what our expectations are based on
their breed. And, you know, that’s totally fine, because that’s why they’re so
much fun to have as pets.”
Emily Anthes is a reporter for The Times, where she focuses on science and health and covers topics like the coronavirus pandemic, vaccinations, virus testing and Covid in childr
.webp)
.webp)
.webp)
.jpg)
.webp)
