Thursday, November 10, 2011

Some Thoughts On The Evolution Of Dogs

Let me begin though with David W. Anthony's musings about the domestication of horses from his book The Horse The Wheel And Language:

Modern horses are derived from very few original wild males, and many, varied females.

In wild horse society there is a female hierarchy and mares are disposed to follow the lead of a dominant mare. Stallions on the other hand are more independent and react violently when confronted.

...A relatively docile and controllable mare could be found at the bottom of the pecking order in many wild horse bands, but a relatively docile and controllable stallion was an unusual individual - and one that had little hope of reproducing in the wild. Horse domestication might have depended on a lucky coincidence: the appearance of a relatively manageable and docile male in a place where humans could use him as the breeder of a domesticated bloodline.

From the horses perspective, humans were the only way he could get a girl. From the human's perspective, he was the only sire they wanted.

Well said!

Horse domestication depended on active selection of traits by humans from the very start. It may have been different for dogs at least in the earliest stages of human wolf interaction suggests naturalist  Mark Derr in an interview on Fresh Air. 

There are many hypothesis on how wolves got domesticated into dogs.

The puppy hypothesis suggests that abandoned wolf puppies were adopted by humans and then the more sociable and docile amongst them were allowed to breed. This involves selection pressures imposed by humans from the very start.

Then there is the garbage midden hypothesis. Wolves started hanging around human camp rubbish sites.  The key element in this hypothesis is that only wolves who were instinctively docile and perhaps not getting enough food in the wild engaged in this behavior. So there was a self selection for docile traits in the wolves who gradually got used to be near humans.

The third is the hunting band hypothesis. Humans began following wolves on hunts or maybe wolves started following humans on hunts.  These bands of wolves became socialized with humans and  isolated from other bands of wolves. Again it is possible that instinctively docile wolves were more likely to follow human hunts if the reward at the end was food which was hard to obtain otherwise. So there is an element of self selection in this hypothesis as well.

Mark Derr tilts towards this third hypothesis. To me, it hard to pick out the stronger contender. The three hypothesis are not mutually exclusive. The thing is that all three situations would have been a common occurrence. For example its reasonable to imagine a scenario whereby a docile male sifting through the garbage dump gets bold enough to latch on to a female adopted as a puppy and living amongst humans.

The three situations would have overlapped many times. Socialization could have occurred via all these three interactions. After that there would have been more severe direct intervention and selection by humans for traits like docility.

There are other interesting questions about dog domestication. For example, was there just one center of domestication or did domestication take place many times in different places? The Middle East is considered the likely place for dog domestication based on  arguments that the dogs from this region show more genetic variation pointing to a source population of greater antiquity. There also have been a case put forward for China being the place where dogs were first domesticated.

Considering the likelihood of repeated contact between wolves and humans there were probably many independent attempts to domesticate the wolf. Fossils of dogs and wolf-dog hybrids as old as 30 thousand years ago have been discovered from various place in the Middle East, Europe and Siberia suggesting multiple domestication attempts, perhaps successful ones.

What comes to my mind is how incredibly violent the initial process of domestication would have been. Wolf-dog pups and young adults not to the liking of humans in terms of their temperament and behavior and form would have been put to death often by a whack to the head.

As a dog lover I shudder at the thought.

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