Natural History

Humans have an aversion to inbreeding. We find the idea of two humans from the same family marrying and having children quite disgusting.

We also know that wild dogs have strong inbreeding avoidance behavior. Wolves and African wild dogs generally avoid mating with blood relatives. Most domestic dogs will mate with their relatives without reservation, and inbreeding has been a tool that dog breeders have used for centuries to establish type and promote homogeneity in their strains.

I have been a critic of inbreeding domestic dogs, but I now realize that I was cherry-picking the science a bit and playing up to human aversion to inbreeding to give a fully nuance and accurate understanding of what inbreeding can do to domestic dogs.

Inbreeding does tend to reduce MHC haplotype diversity over time, which can make dogs more susceptible to various maladies.  It also can increase the chance of deleterious recessive alleles from being inherited homozygously.  All of these are potential risks from inbreeding.

However, I would be remiss to say that inbreeding has not always been a horrible.  Indeed, certain breeds have been founded through a rigorous inbreeding and selection process that surely cannot be thought of as entirely disastrous to the strain.

A few years ago, I came across a book called Working Sheep Dogs: A Practical Guide to Breeding, Training and Handling by Tully Williams. In the text, Williams refers to Kyle Onstott’s work on dog breeding in which Onstott mention an experiment at the Wistar Institute involving rats. A “Miss King,” writes Onstott, bred rat siblings for twenty generations with a strong selection for vigor and stamina, and after twenty generations, she produced a strain of rats that were longer-lived, larger, and generally healthier than the average laboratory rat.

Onstott was a dog breeder and novelist, and his book on dog breeding was considered revolutionary when it was published in 1962. It is called The New Art of Breeding Better Dogs, and I have been trying to get my hands on a copy.  However, I was able to glean from the names mentioned in Williams’s quote of Onstott that the “Miss King” of the Wistar Institute is Helen Dean King.  Dr. (not “Miss”) King was one of the early researcher on the question of inbreeding, and one of leading lights of the Wistar Institute’s rat breeding experiments.

I was able to find her study in which she was able to create the super rats strain through inbreeding, and yes, she was able to do so through rigorous selection for vigor.

In dogs, it is difficult to find a similar experiment, but then I realized one was quite literally staring me in the face.

Most are unaware that German shepherd dogs are all quite closely related to each other. Yes, they appear to have a lot genetic diversity, because we have all these quite different working and show-bred forms, but they all derive from a very similar inbreeding experiment to the one that Dr. King performed at the Wistar Institute.

Max von Stephanitz based the breed upon a Thuringian sheepdog named Horand von Grafrath, which he then bred to Bavarian and Swabian/Württemberg sheepdogs. He then tightly bred upon the progeny. Indeed, the entire breed is based off of three grandsons of Horand. They were Beowulf, Pilot, and Heinz von Starkenburg. They were bred mostly to other descendants of Horand, and there was strong selection for temperament and vitality in the population. It is in these foundations of the breed that wolf may have been added, but the breed still derives from these three grandsons of a single dog.

We can have lots of debates about this in the comments, but the German shepherd dog as an entire breed is fairly healthy for a large breed dog.  In that inbred population, the deleterious allele that leads to a degenerative myelopathy was part of the founders, and the breed itself does have that issue.  Some eye issues were also part of the founding population.

However, if inbreeding were always such a terrible thing, every dog in the breed would be a genetic basket case. Regardless of what one might think about show dogs, the working police and military dogs derive from this exact same inbred population, and it would be folly to say these dogs lacked vigor or were universally unhealthy and unsound creatures. Indeed, it can be argued that the most useful dog ever bred was the German shepherd dog. It has that much utility in a variety of situations.

Now,  I am not saying that inbreeding problems don’t exist. I am saying that we need a nuanced understanding of what inbreeding can do to dog populations, and it is not universally a horrible thing.

Inbreeding and rigorous selection can be a good thing for a strain.  Of course, I know there are breeds that do need some genetic rescue. The Doberman pinscher was founded in much the same way as the German shepherd, using a much more diverse group of domestic dogs in the foundation strain. However, the breed suffers so much from inherited DCM that it an outcross program could very well be justified.

But those of us who advocate rationalism and science in understanding and caring for dogs must keep an open mind. We must look at all the objective science and avoid appeals to human prejudice.

That’s what I’ve tried to do here. I am correcting some of my earlier errors, and I hope this helps lead to a more nuanced view of the subject.