Looking at normal dogs’ brains shows how “fighting breed” brains differ

BOSTON, POMONA––There may already be weeping and gnashing of teeth among pit bull advocates, and perhaps significant fundraising underway to trump up rebuttals, too, following the September 2, 2019 Journal of Neuroscience publication of “Significant neuroanatomical variation among domestic dog breeds,” by Harvard University evolutionary neuroscientist Erin Hecht.

Authors did not go looking for trouble

Hecht and five distinguished co-authors did not set out to pick a fight with organized pit bull advocacy.

In truth, Hecht et al largely side-stepped the pit bull-related implications of their findings in their article and post-publication statements.

Yet Hecht et al demolished the bedrock creed of pit bull advocacy that canine form, function, and behavior are inherently unrelated.

By looking at how form, function, and behavior are related, across a broad spectrum of breed types produced by humans to perform a range of specific tasks, Hecht et al in addition pointed the way toward recognizing what specifically makes pit bulls by far the most dangerous breed category, even though only one acknowledged pit bull was part of their study.

Basis for scientifically defining pit bulls

Hecht et al further established a basis for scientifically defining a pit bull, which can be refined through follow-up studies, by recognizing physical traits that signal a propensity toward violence, as well as the capability for doing violence.

This would bypass the difficulty of using DNA to identify pit bulls, much exploited by lawyers and lobbyists employed to fight breed-specific legislation.

As the Mars Wisdom Panel web site recognizes in explaining why DNA testing is an inappropriate tool for defining pit bulls, “The term ‘pit bull’ does not refer to a single recognized breed of dog, but rather to a genetically diverse group of breeds which are associated by similar physical traits,” specifically those favored by dogfighters.

Each fighting dog breeder had own genetic formula

“Due to the genetic diversity of this group,” the Mars Wisdom Panel web site continues, “Wisdom Health cannot build a DNA profile to genetically identify every dog that may be visually classified as a pit bull. When these types of dogs are tested with Wisdom Panel, we routinely detect various quantities of the component purebred dogs including the American Staffordshire Terrier, Boston Terrier, Bull Terrier, Staffordshire Bull Terrier, Mastiff, Bullmastiff, Boxer, Bulldog, and various other terriers and guard breeds.

“Additionally, there are often other breeds outside of the guard and terrier groups identified in the mix, depending on each dog’s individual ancestry,” which may vary widely, not only through the influence of accidental random breeding, but also because dogfighting breeders have often developed their own customized breed lines by mixing in genetics from, for example, Rottweilers to increase size and German shepherds to whet reactivity.

Further study likely to strengthen findings

While the DNA of a pit bull may be scrambled, however, the outcome is so similar that “pit bull” has for decades been among the breed types most often recognized by people offering dogs for sale or adoption in classified ads.

What Hecht and team most clearly demonstrated is that form, function, and behavior in dogs are very closely linked, especially in breeds originally developed for fighting––and that this is true even when the definition of a “fighting breed” is broadened to include, as they did, dog lines such as Boston terrier and boxer that have not been bred to fight in approximately 80 generations.

Narrowing the definition of a “fighting breed” down to just dogs recognized as pit bulls, and looking at a much larger number of pit bulls, is expected to confirm and reinforce the findings, not because of what Hecht et al discovered about pit bulls in specific, but because of what they discovered about how the relative size of six specific brain regions correlates with behavior in all dogs.

Pit bull appearance linked to brain structure––and behavior

In simplest terms, if a dog has the blocky head shape and oversized jaws characteristic of a pit bull, a magnetic resonance imaging scan is likely to identify the brain structures associated with sudden, random, unpredictable violence and “dead game” fighting behavior as well.

Co-authors, along with Hecht, of “Significant neuroanatomical variation among domestic dog breeds” include Stony Brook University anthropologist Jeroen B. Smaers, Ph.D.; William J. Dunn of the Michigan State University Department of Psychology & Neuroscience; University of Georgia at Athens professor of neurology and neurosurgery Marc Kent; and Emory University neuroscientists Todd M. Preuss, Ph.D. and David A. Gutman, M.D.

62 dogs, 33 breeds, 10 functions

“Significant neuroanatomical variation among domestic dog breeds” opens by explaining that the team “assessed regional volumetric variation in MRI studies of 62 male and female dogs of 33 breeds.”

The dogs were divided into ten categories reflecting the historical purposes for which they were most often bred: bird flushing and retrieval; explicit companionship; guarding, protecting, and sentinel work; herding, police and military use; scent hunting, sight hunting, sled-pulling, sport fighting, and vermin control.

The sampling of breeds considered to have been developed for sport fighting included one 2-year-old male pit bull; two male Boston terriers; four boxers, three male and one female; and two male bulldogs. Whether these were “American bulldogs,” a common type of pit bull, or English or French bulldogs was not specified.

Spatial allocation of brain regions shows behavior

Many of the dogs were evaluated as possible members of several different purpose groups. Boxers, for instance, were evaluated as potentially part of four purpose groups; Boston terriers as part of three purpose groups.

In other words, Hecht et al did a study of the spatial allocation of dogs’ brains somewhat analogous to comparing how a variety of nations allocate employment and national budget, including for both civilian and military purposes, and then comparing the findings to those nations’ political postures.

Typically the most militaristic nations will employ the most people as soldiers and spend the most money on weapons.

“Neuroanatomical variation plainly visible across breeds”

“Notably, neuroanatomical variation is plainly visible across breeds,” Hecht et al found. “This variation is distributed non-randomly across the brain,” Hecht et al wrote.

To extend the analogy to a comparative study of nations, the proportion of a national labor force and national budget allocated to preparation for war has much less to do with the size of the nation than with the attitude of the nation toward neighbors and cultural or economic rivals.

As Hecht et al put it in their “Significance statement,” near the top of “Significant neuroanatomical variation among domestic dog breeds”:

“Neuroanatomical variation is not simply driven by brain size, body size, or skull shape. Nearly all of the identified variation occurs in the terminal branches of the dog phylogenetic tree, indicating strong recent selection in individual breeds. These results indicate that through selective breeding, humans have significantly altered the brains of different lineages of domestic dogs in different ways.”

“Massive natural experiment”

Hecht et al initiated their study, they explained, because “A major goal of modern neuroscience is to understand how variation in behavior, cognition, and emotion relates to underlying neural mechanisms. A massive ‘natural experiment’ in this arena has been right under our noses: domestic dogs. Humans have selectively bred dogs for different specialized abilities.”

The outcome, over centuries, is that “Significant breed differences in temperament, trainability, and social behavior are readily appreciable by the casual observer, and have also been documented quantitatively. Recent genetic research indicates that this behavioral variation is highly heritable.”

Which is to say that behavioral variation from one dog breed to another does not occur by accident. Herding breeds herd, bird retrieving dogs swim, racing dogs run, and scent hounds sniff.

“This panoply of behavioral specializations must rely on underlying neural specializations,” Hecht et al emphasize.

Breeds “developed in an intentional goal-driven manner”

“Most modern dog breeds were developed in an intentional, goal-driven manner relatively recently in evolutionary time,” Hecht et al recognize, “between the past few thousand to the past few hundred years. This strong selection pressure suggests that brain differences between breeds may be closely tied to behavior.

“However, selection also occurred for outward physical appearance,” Hecht et al acknowledge, “including craniofacial morphology. This may have placed constraints on the internal dimensions of the skull, which may in turn have had secondary effects on brain morphology. There is substantial diversification of skull shape across dog breeds, and this has been linked to behavioral differences.

“Alternatively, neuroanatomical variation may be explained primarily by body size,” Hecht et al concede, “with different breeds’ brains representing minor, random, scaled-up or scaled down variants of a basic species-wide pattern.

“Any attempt to determine whether breeding for behavior has altered dog brains would have to be able to differentiate between these competing (and potentially interacting) hypotheses. A simple comparison of regional volumes would be insufficient.”

Pit bulls vs. golden retrievers

For example, Hecht et al explain, “A significant difference in the volume of, for example, the amygdala in pit bulls versus golden retrievers might seem intuitively meaningful, but in order to ascertain whether such a difference was truly the result of selection pressure on behavior, the phylogenetic structure of the dog family tree needs to be taken into account in order to partition variance attributable to inheritance.”

This is what the research behind “Significant neuroanatomical variation among domestic dog breeds” did.

Most of the highly technical paper describes the methodology of the MRI analysis, done to distinguish what parts of the canine brain evolved first, and are therefore shared in more or less equal proportion among all dogs, versus what parts have taken on different proportions during the relatively brief time in which dogs have been selectively bred by humans.

Dog brain size does not scale with body size

“We found that dog brain sizes do not scale commensurately with body sizes,” Hecht et al restate.

Further, “A phylogenetic analysis revealed that changes in brain size are not predicated by relatedness, and are more likely the result of selection on terminal branches of the phylogenetic tree (i.e. individual breeds).

“Brain evolution in domestic dog breeds follows a ‘late burst model,’ with directional changes in brain organization being primarily lineage-specific,” Hecht et al found.

“Six regionally co-varying networks”

These “directional changes,” either enlarging or shrinking particular parts of the canine brain to enhance particular specialized abilities, occurred in what “Significant neuroanatomical variation among domestic dog breeds” terms “six regionally covarying networks.”

These networks govern response to drive and reward; scent in combination with recognition of food; movement, eye movement, and navigation; social action and interaction; the hypothalamic-pituitary-adrenal axis, associated with fight-or-flight responses to fear, stress, and anxiety, and in particular, in dogs, with aggressive behavior; and olfaction working in combination with vision.

A table in “Significant neuroanatomical variation among domestic dog breeds” shows the findings from the MRI analysis, alongside a color scale illustrating relative scientific significance.

Intersections

Among the 60 intersections of the ten dog purpose categories with the six “regionally covarying networks,” the most significant is that of dogs bred for vermin control with social action and interaction. The breeds in this category include Boston terrier, dachshund, Jack Russell terrier, miniature schnauzer, silky terrier, West Highland white terrier, wheaten terrier, and Yorkshire terrier.

The second most significant intersection is that of dogs bred for police and military use with the “regionally covarying network” for olfaction working in combination with vision. These breeds include boxers and Doberman pinscher.

German shepherds and Malinois, the breeds most often associated with police and military use, were not included in the study, but their combination of acuity of scent and vision has been identified by other studies as exceptional.

“Fighting breeds” & “fight or flight”

The third most significant intersection is that of “fighting breeds” with fight-or-flight responses to fear, stress, and anxiety, commonly identified by trainers as “triggers” to attacks.

Another way to express the findings of “Significant neuroanatomical variation among domestic dog breeds” would be to state that the traits of all dog breeds originally developed for purposes other than vermin control are less distinctively significant than the capacity of small terriers for social action and interaction.

The most distinctive traits of dog breeds originally developed for police and military use have more significance than 97% of the other intersections between dog form and function.

Finally, the brain adaptations associated with fight-or-fight response are more significant in “sport fighting” breeds than 95% of the other intersections between dog form and function.

Pit bull breeders already did the experiment

Conclude Hecht et al, “In all six of the regionally covarying networks we found, significant correlations were found with at least one behavioral specialization.”

Looking ahead, toward further research, Hecht et al suggest that, “It might be possible, for example, to identify neural features that are linked to different breeds’ specializations for specific behaviors, and to selectively breed or train dogs for enhanced expression of those neural features.”

This is, of course, exactly what pit bull breeders have always done, including John P. Colby, originator of the “Staffordshire” line, and John D. Johnson, who developed the “American Bulldog,” also known as the “Ambull” and “American Bully.”

Authors assumed all dogs in the study were pets

Offered Science News neuroscience writer Laura Sanders, who holds a Ph.D. in molecular biology from the University of Southern California, “The MRI scans [used by Hecht et al] were taken of dogs with normal brain anatomy at the Veterinary Teaching Hospital at the University of Georgia at Athens.

“While the study wasn’t designed to directly link brain shape to behavior,” Sanders said, the results offer some hints. Researchers identified groups of brain areas, such as smell and taste regions, that showed the most variability between breeds. Those groups are involved in specialized behaviors that often serve humans, earlier studies have suggested.

“The authors assumed the dogs in the study were all pets. It is possible that dogs extensively trained for specialized work — such as sheep herding, bomb detecting or guiding the blind — might have even more distinct brains,” Sanders speculated.

The most distinctly different brains, however, might be found among dogs who will die and not pass along their genes if they fail at their specialized work.

Fighting pit bulls most clearly fit this definition, with no other breed types even close.

Findings undermine pit bull advocacy witnesses-for-hire

“Significant neuroanatomical variation among domestic dog breeds” undermines in particular the central contentions of Western University College of Veterinary Medicine faculty members Victoria Voith and Kristopher Irizarry, who have often appeared as witnesses-for-hire in opposition to breed-specific legislation.

Voith and Irizarry are also prominent members of the National Canine Research Council, a front for the pit bull advocacy organization Animal Farm Foundation, and of several other pro-pit bull lobbying and promotional entities.

Irizarry succinctly summarized their arguments in an August 17, 2011 deposition in a lawsuit that sought to overturn a pit bull ban in Moses Lake, Washington, in which he also stipulated that his fee would double from $50 an hour to $100 an hour if obliged to testify in person.

Brain anatomy trumps “breed”

“A mixed breed dog is not a member of a breed,” Irizarry asserted.

But if, as Hecht et al found, form, function, and behavior are intertwined traits, the brain anatomy of any specific dog is more indicative of what the dog may do than the breed identity suggested by DNA testing, and visual appearance is strongly indicative of brain anatomy.

Claimed Irizarry, “The anatomical features associated with dog breeds do not encode the brain or the connections of brain cells and are not involved in encoding the behavior of a dog.”

“Significant neuroanatomical variation among domestic dog breeds” renders this statement wholly false.

Visual identification of dog breeds

Contended Irizarry, “Visual identification of dog breeds is inaccurate.”

But “Significant neuroanatomical variation among domestic dog breeds” suggests that visual identification of dog breeds is highly accurate as an indication of brain anatomy.

Wrote Irizarry, “The anatomical similarity of dogs within a breed causes people to assume that dogs within a breed share other traits, such as behavior.”

“Significant neuroanatomical variation among domestic dog breeds” indicates that this assumption is correct.

“There is no scientific basis for better-than-chance visually accurate breed identification by animal control officers,” Irizarry claimed, adding that “Animal professionals, including veterinarians, dog breeders, dog show judges, animal control officers and others are not capable of accurately identifying breeds in mixed breed dogs.”

Yet “Significant neuroanatomical variation among domestic dog breeds” suggests that the external shape of a dog’s head correlates at a very high rate of statistical significance with the dog’s behavior, and can be easily recognized by any person of ordinary intelligence.

Argues that dogs were not bred for behavior

“Most people erroneously believe that dog breeds were bred for specific behaviors,” Irizarry alleged, perhaps unwittingly contradicting the common but false pit bull advocacy saw that fighting dogs were bred to be “dog-aggressive” but “human-friendly.”

That dog breeds were bred for specific behavior, Irizarry claimed, “is a stereotype unsupported by the recent scientific findings that identify anatomical traits as the foundation of breed stratification.”

Hecht et al found exactly the opposite, as indicated by canine history: dogs were bred for all of their major roles, and most breed types developed essentially the appearance that they have today, long before exhibition for conformation emerged in 19th century England.

Genetics vs. behavioral conformation

“Once a member of the breed is crossed with other breeds of dogs,” Irizarry contended, “it gains the genetic variation from these other dogs and loses the genetics associated with a single breed.”

Even if true, however, this would be irrelevant. If a dog inherits the brain anatomy specific to any breed historically developed for a particular purpose, the data amassed by Hecht et al indicates, the dog is likely to behave like the breed he or she most resembles.

How behavior is inherited

Wrote dog behaviorist Alexandra Semyonova in The science of how behavior is inherited in aggressive dogs, posted by ANIMALS 24-7 in 2014,“Until recently, most people recognized that much dog behavior is a result of manipulating inheritance: if you want to do sheep trials, you get a border collie. If you get a beagle, he will likely become instantly deaf to your calls if he picks up a scent to track.

“But after discussion started about perhaps banning breeds who often attack and kill,” Semyonova continued, “defenders of these breeds began to dispute the heritability of any kind of dog behavior.

“Only when behavioral inheritance is understood,” Semyonova emphasized, “beginning with basic biological concepts, can we have a clear and honest discussion about aggression in domestic dogs. First we must understand the relationship between ‘physical conformation’ and ‘behavioral conformation,’ which may be seen as opposite sides of the same coin.

“Selecting for very specific abnormalities in the brain”

“Physical conformation” describes how a dog has been bred to become physically shaped specifically for the task we want him to perform. The purpose-bred dog’s body––brain, skeleton, muscles, and metabolism––will be different from those of other dogs. The dog will feel physically comfortable doing the job, whatever it is.

“Selection for aggressive performance,” Semyonova specified, “includes consistently selecting for very specific abnormalities in the brain,” such as Hecht et al discovered.

“These abnormalities appear in many breeds of dog as an accident or anomaly, which breeders then attempt to breed out of the dogs,” Semyonova noted. “In the case of the aggressive breeds, the opposite occurred. Rather than excluding abnormally aggressive dogs from their breeding stock, breeders focused on creating lineages in which all the dogs would carry the genes causing them to reliably exhibit the desired impulsive aggressive behavior.”

“Huge contradictions in pit bull behavior”

Testified ANIMALS 24-7 artist, photographer, researcher, and social media editor Beth Clifton in her January 2018 essay Are pit bulls monsters or are they just dogs?, “There are huge contradictions in some of the behavior we see in pit bulls, who often veer back and forth from affectionately ‘sweet’ and ‘goofy’ to inflicting mayhem, and yet these contradictions occur consistently in practically all pit bulls. We see in these dogs a lack of impulse control, hyper reactivity, fearfulness and anxiety, among their most basic and universal traits.

“I can attest to this myself,” Beth wrote, “having been exposed to a great many pit bulls in my previous capacities as animal control officer, veterinary technician, former pit bull owner and rescuer, and now outspoken advocate for public safety, including effective breed-specific legislation.”

Scientific support

The findings of Hecht et al relative to the exaggerated size of the “fighting breed” brain region associated with the hypothalamic-pituitary-adrenal axis, specifically linked to fight-or-flight impulsive responses to fear, stress, and anxiety, including aggressive behavior, offer scientific support to Beth’s observations.

Beth’s observations are, after all, essentially the observations of practically anyone familiar with pit bulls––except, of course, pit bull advocates defending their breed against the reality that pit bulls are 5.8% of the dogs in the U.S., responsible for 59% of the dog attack fatalities and 76% of the dog attack fatalities among humans, and well over 90% of the dog attack fatalities among other animals.

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