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  • Writer's pictureDr Mark J Tenenbaum

Popular Dog Breeds: 100 Years of Breeding.

Dogs have been human's furry companions for thousands of years, but they haven't always looked the way they do now. Many popular breeds have changed physically over the past century, thanks to (of course), humans.

As humans have identified particular traits in different dogs such as; size, coat quality/colour, facial features, demeanour etc, this has led to selective breeding (only allowing specific dogs to mate with other dogs). Via this process of breeding, humankind has created at least 167 different breeds or groups of dogs with unique physical and mental characteristics. All of these different "breeds" still belong to the same species.

Science and Dogs have put together a side-by-side comparison of different popular dog breeds from 1915 till 2017. The images on the left are from the 1915 book 'Breeds of All Nations' by W.E. Mason.


Bull Terrier

It seems incredible to think that at some time in history the bull terrier was a handsome, athletic breed. Somewhere along the way, their skull changed form and they developed a thicker abdomen. To add, they also picked up some other features including supernumerary teeth and compulsive tail-chasing.

Basset Hound

To summarise the changes the basset hound has experienced; lower stature, changes to rear leg conformation, excessive skin, vertebra complications, droopy eyes prone to both entropion and ectropion and excessively large ears.


A shorter face means a whole host of complicating problems. The modern boxer not only has a shorter face, but the muzzle is also slightly turned upwards. The boxer (like all brachycephalic breeds) can have difficulty in breathing and regulating their body temperature due to their compromised respiratory tract. The boxer also has one of the highest rates of cancer.

English Bulldog

The English bulldog is a breed that has almost acquired all possible deleterious breed predispositions over the past century. A 2004 survey by the Kennel Club found that the breed die at a median age of 6.25 years (n=180). There is no such thing as a completely "healthy" English bulldog due to their complications.


The dachshund previously had functional legs and a neck size that was appropriate to the rest of its body. Both the dachshund's neck and back have gotten longer, their chest now protrudes further forward and their legs have shrunk to the extent where there is very little clearance to the ground. The dachshund is the breed with the highest risk of intervertebral disc disease (IVDD) which can lead to paralysis and other concerns.

German Shepherd

If you ask nearly any german shepherd owner, they will be aware of the hip and musculoskeletal concerns with this breed. In the 1915 book 'Dogs of All Nations' the german shepherd was described as medium-sized dog (25kg). This is quite different to the breed we see today; angulated, barrel-chested, sloping back, ataxic 38kg dog.


The pug is another prime example of a brachycephalic breed and therefore they experience all the complications that arise from such a conformation. In addition to these problems, they also experience dentition issues, skin and musculoskeletal concerns.

St. Bernard

Once a noble working dog, the modern St. Bernard has been oversized, had its face squished in, and bred for abundant skin. Some of the diseases these dogs are predisposed to include; entropion, ectropion, haemophilia, osteosarcoma, fibrinogen deficiency.


Now, it is completely reasonable that all breeds will have some predispositions to specific diseases. But, the concern with our selective-breeding, is when we select for traits that are NOT in favour of the animal's interests or welfare.

Yes, we have clearly changed these breeds over time (more so for the worse), but we can still rectify these changes and start to select for traits that are favourable and will benefit the dog. Examples can include breeding brachycephalic breeds with longer muzzles, breeding St. Bernards with less skin folds, breeding german shepherds that have been diagnosed free of hip, elbow dysplasia.

This blog has been based on the original blog 100 Years of Breed "Improvement"

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