We may have been able to tame the dog – the only large carnivore to now happily coexist with humans. But how does domestication occur and can we learn from it to develop new animal breeds and crop varieties for food?
Humans have a long tradition of taming their environment and the species that live around them. Known as domestication, the process may occur deliberately or more indirectly.
An example of deliberate domestication is the selection of the largest, most docile cattle to keep close to a village, and then selecting the largest, tastiest individuals to use as breeding stock, which continues over generations. Indirect domestication also occurs, for example, cats coexist with humans, both gaining mutual benefit, the cat receiving food and shelter, and the people benefit from having a predator to control pests like rats that can diminish stored harvests.
Interestingly the dog is thought to have been the first animal domesticated by humans at least 10,000 years ago, but maybe as old as 38,000 years ago. Dogs were probably domesticated due to their trainable nature (by comparison cats are not easily trainable – I’m sorry cat lovers but you know it’s true).
This made dogs useful as guards, hunters, shepherds, pack animals, sled pullers and even companions.
The howl of the wild
The perceived wisdom is that dogs were domesticated from wolves. Wolves have been around for half a million years, and have at least 32 living subspecies. Interestingly wolves have a highly organised social system. This likely pre-adapted wolves to human domestication. It is likely to be one of the reasons for the strong bond that can be formed between humans and dogs, which is partially facilitated by dogs’ ability to interpret a human’s emotional state based on the individual’s facial expression, a rare interspecies feat.
However, it is still difficult to know exactly when and how wolves were first domesticated. That’s because the dog is the only animal to have undergone the domestication process when humans were still nomadic hunter-gatherers. The templates developed for understanding how other animals were domesticated, after the advent of agriculture, don’t apply so neatly to dogs.
It is easy to imagine that a hand-reared ancestral wolf would have developed an intense, familial bond with humans, and so domestication could easily have proceeded through such ‘wild orphans’. However, it is also fair to say that in the case of dogs, domestication is unlikely to have been simply something humans did to dogs. Both dogs and humans benefit from the close relationship, and so it may have been fairer to say that domestication was something we did with each other.
However as humans spread around the world taking their dogs with them, the dogs will have interbred with local canine species, including wolves, rather confusing their genetic origins. In fact, a DNA study of the modern Eurasian wolf estimates that a significant proportion of the wolf’s genome comes from interbreeding with domesticated dogs.
It likely that dogs were domesticated on multiple occasions in different parts of the word as humans trained wild canine species for different uses.
The face of a wolf
But since dogs are large predators, an additional trait needed to be overcome during domestication – aggression. Animals need to retain sufficient aggression to be useful as guards or hunting dogs, but not so aggressive that they will attack people.
Many dogs today do not look like wolves, they have shorter snouts, and most breeds have less erect ears and tails. In fact, they look more like baby wolves, an effect known in biology as neoteny – the retention of juvenile characteristics in adulthood.
These more dog-like, less wolf-like, physical features may have been an unintended consequence of selecting for lower levels of aggression in early domesticated wolves.
Of relevance here is a long-running, and quite remarkable, Soviet domestication experiment on Siberian foxes. As part of a fox fir farm, multiple generations of foxes were selected based on aggression levels alone. The fox lines were deliberately selected for reduced aggressiveness, to make the animals easier to handle. However, the beauty of the experiment was that lines were also selected for normal levels and even increased levels of aggression. Over time the geneticists on the farm noticed that whilst the physical features of the aggressive lines remained typically fox-like, the lines that were repeatedly selected for decreased aggressiveness, started to exhibit a range of physical features more characteristic of juvenile individuals; i.e. shorter snouts, floppier ears and tails. These are a similar set of characters that are now typically exhibited by a majority of adult dog breeds.
See a video about the Siberian fox experiment below.
What does this tell us about domestication
One of the interesting trans-species learnings from this domestication work is that domesticability may be easier to select for than we may have originally thought.
If we transfer this domestication knowledge from animals to crop breeding, we may be able to rapidly deliver some useful benefits. As the earth’s population grows and we increase crop production by growing plants in ever diverse environments, we improve our crops by breeding in increased environmental resilience and disease resistance. However many of these traits are complex and controlled by numerous genes, and environmental tolerance breeding attempts have in recent years met with more limited success.
A new line of thought in crop breeding is why don’t we start with wild relatives that are already adapted to harsh environments and then breed for domestication traits (which in plants equates to; larger grain size, clumped seed heads, reduced tillering). Such domestication traits may in the end be easier to breed for within multiple new crops lines and species, rather than working with our few flogged out staples.
Such a strategy may also produce a range of new and interesting species and varieties of food and flavours for the ever discerning customer.
Freedman AH, Gronau I, Schweizer RM, Ortega-Del Vecchyo D, Han E, Silva PM, et al. (2014) Genome Sequencing Highlights the Dynamic Early History of Dogs. PLoS Genet 10(1): e1004016. doi:10.1371/journal.pgen.1004016
Larson G, Fuller D (2014) The Evolution of Animal Domestication. The Annual Review of Ecology, Evolution and Systematics 45:115-36.
Palagi E, Nicotra V, Cordoni G (2015) Rapid mimicry and emotional contagion in domestic dogs. Royal Society Open Science 2: 150505. doi.org/10.1098/rsos.150505
Tarlach G (2016) The origin of dogs. Discover Magazine, Wednesday, November 9th.