Tuesday, 21 April 2015

How Wolves Evolved Into Dogs

How the wolf became the dog

There is no doubt now that the domestic dog is a domesticated wolf. It has recently been reclassified by taxonomists as a subspecies of wolf, Canis lupus, so instead of Canis familiaris it is now Canis lupus familiaris. It was almost certainly the first animal to be domesticated but ideas have differed over how this came about.

In 1907, Francis Galton proposed that humans had taken wolf puppies back to their camp and raised them, maybe as playthings for the children, but this view is now seen as naive. You can raise a wolf puppy by hand but you don't get a dog; you get a dangerous wild animal. The genes of children who played with growing wolf puppies would probably have been quite quickly eliminated from the human gene pool as well as the puppies' genes being eliminated from the wolf gene pool.

So, clearly something else happened.

The most likely explanation is now thought to be that wolves domesticated themselves and became dogs in the process. The first phase of this would probably have been wolves scavenging on the refuse tips around human encampments. As humans converted from a mainly vegetarian diet to meat eating as they evolved the ability to hunt in organised groups for large animals so the inedible remains would have to be disposed of somewhere and wolves are almost the ideal scavengers to clear up these remains, not being too fussy about the freshness of the meat and guts they eat or the bones they crush, even getting vegetable supplements from the stomach and intestinal contents of herbivores.

So, humans had an interest in letting the wolves help themselves but not in having the aggressive ones around and the wolves had an interest in not being too shy of humans because the least timid stayed and got the best pickings while the others ran away, so the most successful wolves would have been those with less aggression and less fear. As they became less timid and less aggressive they seem to have changed subtly to be more like dogs with shorter faces. That's not the assertion it might seem because we have a precedent in a related species - the Russian silver fox, which is valued for it's fur.

To establish silver fox farms, Russian scientists had decided the way to tame a fox was to selectively breed from those animals which showed less fear of humans already. Animals which are afraid of humans, or any potential predator, must somehow weigh up when to run away. Animals which have less fear will leave it longer before fleeing so, those with a shorter 'flight distance' will have less fear. The scientists assumed this would have some genetic basis and so would be an inherited characteristic. Part of domestication also involved making them less aggressive and safe to handle, so they were also bred for 'passivity'. By selectively breeding from tame animals they expected the foxes to become progressively more tame, i.e. domesticated, with each generation.

Indeed, this is exactly what happened, but so did something completely unexpected: the foxes changed in their physical appearance and behaviours too, not just tameness. A range of coat patterns emerged, never seen in the wild, in addition to the 'silver' coats, which had, after all been the point of the breeding program in the first place. They retained juvenile traits like a broader skull and submissive behaviour, held their tails up and barked and whined.

These differences are believed to be due to physiological changes, associated with adrenaline production, but forty differences have been found between the genome of the domesticated foxes and farm-raised 'wild' foxes.

Because these morphological changes are also seen in domestic dogs when compared to wolves it is probably safe to assume this potential was in a common ancestor. In fact, it has even been proposed that humans in effect domesticated themselves by being less aggressive compared to other apes in order to work successfully in groups and so underwent some physical changes in the process, including a shortening of the 'muzzle' and becoming more paedomorphic compared to our other ape relatives.

But that explains how wolves probably became tame dogs, and it would have been mutually beneficial for humans to have a pack of docile wolves around to defend the common territory from other predators, but it doesn't explain how dogs became the work-colleagues of humans and the house pets we have today, nor why we think of them more as members of the family, even close friends, rather than just another domestic animal like cattle or hens. We have developed a 'special relationship' with dogs which is much more like our relationship with other humans.

A large collaboration trying to resolve some of the differences that exist in current theories of how and where the dog-human cooperative complex arose has come up with evidence that, at least in some parts of our range, dogs may be been used as beasts of burden, with evidence of distortion of the dorsal spinal process by carrying a heavy load and evidence from the skull that some sort of bridal might have been used. But, there is still no agreement about where dogs were first domesticated or when, with estimates varying between 30,000 and 135,000 years ago with some schools of thought putting the location in Europe and some in Southeast Asia south of the Yangtze River. But then there is no reason why the process should have happened just once and nothing to suggest that early domestic dogs couldn't have gotten regular injections of local wolf genes as they spread along trade routes into other areas.

However, there is archaeological evidence that by at least 12,000 years ago, dogs were regarded as something special; as members of the family. Graves have been found with dogs buried with humans often with the human embracing the dog. Some Native American burial sites consist of graves of both dogs and humans, often in the same grave. So, clearly there was a third phase in this developing relationship.

Now a team from Japan have written a follow-up paper for one I reported on here last June. Just as our relationship with our children is moderated by the 'love hormone' oxytocin, so is our relationship with dogs. Dogs have somehow hijacked our parent-child relationship, moderated as it is by eye gazing, to evoke the same sort of response in us that our children do.

Human-like modes of communication, including mutual gaze, in dogs may have been acquired during domestication with humans. We show that gazing behavior from dogs, but not wolves, increased urinary oxytocin concentrations in owners, which consequently facilitated owners’ affiliation and increased oxytocin concentration in dogs. Further, nasally administered oxytocin increased gazing behavior in dogs, which in turn increased urinary oxytocin concentrations in owners. These findings support the existence of an interspecies oxytocin-mediated positive loop facilitated and modulated by gazing, which may have supported the coevolution of human-dog bonding by engaging common modes of communicating social attachment.

So, because some wolves had the genetic potential to become less aggressive and less timid and because they were able to make use of human refuse, they seem to have settled down in some places to live initially close to us, then, as they became fully domesticated, initially as guards and maybe hunting companions, then as beast of burden, so they moved into a closer relationship with us. It has even been suggested that this relationship with domesticated wolves may have given early modern Europeans the edge over Neanderthals.

The final phase was co-opting the oxytocin-moderated 'love hormone' reflex caused by eye contact which both species had evolved to form bonds with children and close friends, to move into the final close relationship we have today.

The patently obvious thing about this is how all this is the product of genes forming alliances which are mutually beneficial to both species, not for any other reason than that it was possible and it gave more descendant both of domesticated wolves and the humans they cooperated with. Biologically, this can be seen equally as wolf genes co-opting human genes as human genes co-opting wolf genes. It is an example of how genes acting for what can look like purely selfish reason, can produce close cooperation.

And the evidence of DNA in modern dogs, modern wolves, and in ancient dogs and wolves, and the archaeological evidence, though incomplete and still not conclusive regarding time and place, is entirely consistent with an evolutionary process over thousands of years. There is no evidence whatsoever for any intelligent intervention nor of sudden creation in recent history.

Creationists will still need to lie about the evidence if they want their dupes to continue to believe in whatever currently fashionable version of biblical literalism they need them to continue to be fooled by.

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  1. Great post! I suppose the "hijacking" of the oxytocin-moderated parent-child interactions to facilitate human-dog (and especially human-puppy) relationships would be another example of "exaptation", like the bacterial flagellum. It would be interesting to find out if there are comparable underpinnings to other seemingly-similar inter-species symbiotic relationships, like that between aphids and some species of ants.

    Interesting that foxes were never domesticated by early humans the way wolves were, given that the potential is there. Perhaps they were less useful, and there was less overlap between fox and human ranges of habitation.

    Creationists will ignore all this or dismiss it as God working in mysterious ways to make the world more convenient for us, but it's a striking example of the strange and subtle things that natural selection can do.

    1. Thanks. My first thought on domestication of foxes are that

      a) they were too small to be useful as guards or pack animals
      b) they are solitary so might not socialise well with humans nor be any use in hunting
      b) the wolves would have driven them away. This camp aint big enough for the both of us! :-)


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