African Wild Dog

The preeminent evolutionist Charles Darwin postulated that evolution took place gradually, pacing along slowly across the thread of time covering the span of multiple generations. At its most basic evolutionary change occurs as a response to environmental changes, a dynamism that makes pretty logical sense; why after all would an organism undertake the biological expense of morphological and genetic change if there was no call for it? One need only look to the crocodile to see a species that has changed little over 40 million years and yet even today is superbly adapted to excel in its particular environmental niche!

The dog too is another exemplary case of evolutionary success. Descended from wolves there are approximately 400 million dogs worldwide compared to 400, 000 wolves; in other words dogs today outnumber wolves by a multiple of 1000. In fact when one considers when dogs made their debut on earth as a distinct species (widely accepted as anywhere between 15,000 – 10,000 years ago; although the jury is still out concerning the date they first appeared) then the dog’s evolution into the more than 400 breeds that exist today is nothing short of a miracle! Fifteen thousand years on the evolutionary scale of things is no time at all!

Bred For Selectivity?

Popular opinion favors the idea that the dog evolved so rapidly because it was selectively bred by man for particular traits that defined the various dog breeds. Though there is ample evidence that dogs existed 8000 years ago, such evidence of their existence around and beyond 15,000 years ago is scanty at best. Which begs the question, how could a species such as the dog come into its own so thoroughly in the span of a mere 5000 – 7000 years?

This cannot be credited to selective breeding by mankind; Mesolithic humans certainly did not have the time, the tools, the knowledge, the intelligence or a large enough population of tame wolves with which to conduct a successful and trait-selective breeding program. There’s fairly concrete evidence though that a good number of dog breeds were in existence around 3000-4000 years ago and that by the time of the Romans many of the common breeds of today already existed.

Tameness Trait Coincided With Floppy Ears, Barking And Change In Coat Color!

How the dog’s morphology and genetic composition changed so radically from that of the wolf in such a period has for the longest time been quite the mystery. However, as so often happens in these cases, an experimental research conducted on an entirely different animal revealed the clue to how the change came about. In the 1950s, a Russian scientist called Dmitri Belyaev began selectively breeding silver foxes (Vulpes vulpes) solely for tameness. The initial purpose of the experiment was to produce a fox that was more approachable and manageable by humans which would have greatly helped in the breeding and raising of those animals for their fur.

The problem the breeders were experiencing was that despite the fact the animals they were dealing with had been bred in captivity for more than 50 years by no stretch of the imagination could they be considered as tame or domesticated; certainly not in the manner that a dog is! The foxes frequently avoided their keepers, sometimes even bit them, and at other times the animals harmed themselves in an effort to evade their keepers.

Belyaev and his colleagues thus selected the foxes that exhibited the least fear/shyness of people for their breeding program; their aim was to selectively breed for a tame trait. With successive generations of selective breeding the foxes became tamer and tamer such that by the eighteenth generation they had bred a fox that exhibited all the characteristics of a domestic dog. The foxes would actually approach people, clamber over them, roll over to get their bellies tickled and even answered to their names.

Perhaps the most surprising aspect of the selective breeding program was that the foxes no longer resembled foxes but looked and acted like dogs. The coats of the foxes were no longer the characteristic silver fur much sought after by the fur industry but were black and white piebald instead. What is more, the foxes’ tails were curly and upward turned, their ears were floppy and to crown it all the animals even barked like dogs! Dmitri Belyaev had not sought nor bred for these characteristics but all the same they still manifested!

A subsequent investigation into the unexpected side effects revealed that breeding for tameness set off an entire cascade of hormonal changes in the animals. It was observed that the “domesticated” foxes had considerably lower levels of adrenaline which explained their tameness (reduction in flight-or-fight reflex) but didn’t explain the other observed changes. However it didn’t take long before Belyaev and his colleagues made the connection; the hormone adrenaline shares a biochemical pathway with melanin, a hormone that plays a significant role in an animal’s coat color.

Simply put, selective breeding for the tameness trait set off and stimulated an entire slew of genetic changes within the animals in a surprisingly short period. It is now widely believed that the wolf underwent a similar transition to eventually evolve into the domestic dog.

Around 54 to 38 million years ago a new line of meat-eating mammals evolved. They became known as the carnivores and were distinct from all other meat eaters for the fact they possessed a unique feature – four carnassial teeth. Only carnivorous mammals possess teeth that adapted from a crushing chewing mechanics to a tearing and ripping mechanism facilitating cutting through flesh.

Modern day carnivores are believed to have evolved from two separate ancestral lines at some point:

1. Hesperocyon which habited North America 38-26 million years ago. This was perhaps the first genus to have developed an inner-ear anatomy a feature characteristic of the canine family.

2. Amphicyon which dominated the Eurasian continent for millions of years inter-lapping the same time frame as Hesperocyon. However somewhere along the line it is believed that the Amphicyon line died out.

Around 26-7 million years ago during the Miocene era Hesperocyon evolved into 42 different genera of canines with dog-like features of which Leptocyon (12 million years ago) an evolutionary descendant of Hesperocyon eventually evolved into the Canidae from whence came the modern canids which include wolves, foxes, jackals, coyotes and of course dogs.

Interestingly enough up until 10-20 million years ago bears and dogs were actually members of the same family before their evolution diverged to continue along separate paths. The ancestors of dogs are known to have evolved in response to climatic changes as well as changes to the environment. As tropical forests were superseded by vast areas of wide open savannah and steppes, so came into being the large herds of herbivores that are still present today in Africa.

Where beforehand the dog may have been a solitary hunter with the change in the environment it became expedient for the dog to evolve into a pack animal with a well formed social stratum. In this way dogs were able to successfully hunt and tackle the much larger prey that was characteristic of the grazing herds of herbivore. This pack mentality is still evident in the domestic dog as witnessed by roving packs of stray dogs in urban areas.

It is this innate ability of dogs to develop social relationships (inherited from wolves from which the domestic dog was bred) that is the basis of their success as a species!

Article on dog evolution written by Kayye Nynne