As the old saying goes, the dog is indeed “man’s best friend.”
Annals of history and folklore have depicted the human-canine bond as a profound relationship cemented in the virtues of love and trust that traces back to time immemorial.
From cave paintings to parchment scrolls, our ancient forefathers have repeatedly boasted of the firm ties they enjoyed with their fur pals.
Evolutionary biologists and anthropologists say the first animals domesticated by humans were dogs. Long before the advent of agriculture and development of livestock husbandry, man had already befriended dogs.
Or, was it the other way around? Did dogs adopt humans, and channelize the evolution of the bond that modern humans and dogs share?
|Did dogs actually adopt us to begin with?
But how did it all start? How did humans bond with their first dogs?
Based on recent scientific literature this article focuses on the following themes:
- Where, why and how did dog domestication occur?
- How the human-dog bond shaped human and dog evolution?
In this article:
Conflicting theories exist related to exactly where and when was the modern dog domesticated by humans. However, we can safely consider the following historical picture in our minds.
Let us go back around 23,000 years ago. The last Ice Age was ending. Ancestors of modern humans were adapting to a hunter-gatherer lifestyle.
Among the wolf populations that lived at that time, one group was evolving to be apex predators. This group likely are the forefathers of the modern wolves, particularly, the gray wolf.
In that era, a second group of these ancient wolves were perhaps keeping an eye on the human hunter-gatherers for reasons far more complex than simply preying on them.
These prehistoric wolves were fascinated to see another animal (early humans) that thrived by social partnership within large groups.
Like wolves, humans hunted in packs as well as protected each other from predators.
Then, after the hunt was over, these human groups would have shared a barbeque.
Wouldn’t the smell of burning meat attract this group of wolves that was closely following the footsteps of our forefathers?
Further, for getting the prized food, these wolf-like carnivores did not even have to get into any competition with the humans; for, the humans ate most of the meat but nevertheless, a lot of the carcass, bits and the bones were left for the wolves to scavenge without any hindrance.
Remarkably, we humans can rely on animal protein for only about 20% of our dietary needs.
Thus, especially in winter months, fats and oils of the hunted game would be essential for the hunter-gatherers, but a lot of the exclusively protein-rich meat would be ignored.
These lean meat cuts would be readily and gratefully accepted by the wolves.
This is termed as the food partitioning theory, where humans and their early wolf-like canine partners amicably partitioned the hunted meat between themselves to limit food competition.
Further, since these human groups lit fires at night to keep warm and to ward off predators, these wolves perhaps recognized the value of staying close.
Hence, these ancestral wolves learned that following humans without preying on them meant free food and safety.
Interestingly, some reports described wolf populations even in the modern era that show enthusiasm toward socializing with humans they encounter.
Particularly, in Alaska, a wolf has been reported to have been friendly with both humans and dogs.
In northern Canada, as well, wolves have been reported to approach human settlements curiously and amicably.
The exact timing of when wolves became domesticated dogs is still controversial. However, we can consider with certainty that by at least 15,000 years ago, humans had already domesticated dogs.
Bones found in the Bonn-Oberkassel region of Germany are widely recognized as the remains of the earliest dog confirmed to date.
Modern science confirmed this dog died young around 14,200 years ago and could not be of much economic importance to its human companions.
Despite that, the dog was buried with care. This indicates a deep human-dog bond that was already established in human societies of those times.
Further, Pontus Skoglund, a world-renowned evolutionary biologist, explained in a groundbreaking 2020 study published in “Science,” around 11,000 years ago there were distinct lineages of modern dogs for each of these geographical niches: Siberia, New Guinea, Asia, the American continents, and northern parts of Europe.
Since so much diversity had set in even within modern dog genetics, evolution and domestication already took place long before that.
In terms of the real ancestor of modern dogs, some scientists consider the modern gray wolf as the most likely.
Others suggest that a now-extinct ancient wolf population gave rise to gray wolves, as well as giving rise to the modern dog.
Figure 1. Two thoughts about the ancestral species of the modern dog. The first thought: gray wolves are most likely to be the ancestor of the modern dog. The second thought: a now-extinct ancient wolf population gave rise to the gray wolf and the modern dog.
Much like the timing of dog domestication, at least two schools of opinion exist regarding the geographical site where the domestication occurred.
To avoid controversy, let us briefly discuss the rationale put forth by each scientist group, without trying to draw any definitive conclusions about the exact location of dog domestication.
A representation of the possible dog domestication theories has been depicted in the figure below.
Peter Savolainen is a big name in evolutionary genetics. His group has been a strong proponent of the theory that modern dogs were domesticated in Southeast Asia, specifically somewhere south of the Yangtze River in China.
Figure 2. This figure depicts the possible sites of dog domestication and the routes of global dispersal of the modern domestic dog.
In a “Science” article from 2002, Savolainen’s group reported a phylogenetic study on mitochondrial DNA of 654 representative modern dog populations.
Based on complex phylogenetic data, which indicated greater genetic variance in East Asia than seen in other geographical locations, they proposed that modern domesticated dogs originated in East Asia about 15,000 years earlier.
In further studies from 2009, and 2011, they showed that the complete range of genetic diversity of modern dogs was found in geographies south east of the Yangtze river in China.
Genetic diversity gradually decreased as the sampling was moved across Eurasia. This is consistent with the argument that modern dogs arose in southeast Asia; highest levels of genetic variability in an animal are seen in locations of its emergence.
In concordance with this information, in 2013, Savolainen’s group showed that immunity-related genes of the Major Histocompatibility Complex (MHC) had maximum diversity amongst southeast Asian dogs when compared to European breeds.
This corroborates this group’s 2012 work that similarly showed maximum genetic diversity in the Y-chromosome sequence of southeast Asian dog populations.
In 2016, bio-archaeologist and fossil genomics specialist Greger Larson at the University of Oxford published his hypothesis about dual domestication of modern dogs “Science.”
Larson’s group analyzed DNA from 59 ancient dogs and the entire genome of an Irish dog that lived in the late Neolithic age.
In their study they found a deep genetic split between early dogs of east Asia and west Eurasia. Based on these data they argued dogs were dually and simultaneously domesticated from two separate wolf communities in two geographies of the Old World: east Asia and west Eurasia.
In his 2017 “Nature Communications” study, SUNY Stony Brook-affiliated population evolution biologist Krishna Veeramah strongly refuted Larson’s dual domestication hypothesis. His data suggested a single geographical origin of modern dogs dating back to 20,000 – 40,000 years ago.
A big school of evolutionary biologists champion the dogma that modern dogs arose once and in Eurasia.
Swedish geneticist Love Dalen made a discovery in 2010.
From the Taymyr peninsula in Siberia, he found a 5-cm wolf bone. Using modern paleobiology techniques, his group inferred that this bone was of an ancient wolf that lived in Siberia about 35,000 years ago.
Further data he reported in “Current Biology” suggested that around 27,000 years ago, wolves in that region gave rise to gray wolves, modern dogs and another ancient wolf population called Taymyr wolf.
Paleoscientist Robert Wayne from the University of California considered this information congruent to his own arguments that modern dogs originated in Europe around that timeframe.
Another PNAS (the prestigious Proceedings of the National Academy of Sciences) report from 2020 indicates Siberia as the niche of dog domestication around 23,000 years ago.
This study suggests that both early human settlers of North America and ancient American dogs arose in Siberia around 23,000 ago. They entered America about 16,000 years ago and then split into multiple groups.
The authors hypothesized that a group called ancient north Siberians domesticated the modern dog 23,000 years ago. Further, they either traded or migrated their dogs with them as they split into groups and entered America and Eurasia. This explains the earlier enigma why modern dogs appeared in Europe and America 15,000-16,000 years ago.
As the human-dog bond developed and solidified, the wolf ancestors of modern dogs slowly transitioned into dog-like wolves and then to wolf-like dogs and finally to bona fide dogs. Let us peek into the science of the actual changes that happened alongside this metamorphosis.
Modern dogs have undergone genetic diversification from their wolf ancestors via both natural and human selection. Nevertheless, dogs still resemble wolves in a lot of ways.
In fact, a 2016 report indicated dogs were genetically different from wolves in only 11 genes.
It is not surprising the genetic origin of fur color of modern dogs and wolves overlap. Studies show that genetics of coat color of modern dogs and wolves have evolved via natural selection.
During the domestication process, ancient dogs greatly separated from their wolf brethren in their dietary habits.
Perhaps the most remarkable change in this regard is the ability of dogs to transition from the protein-heavy dietary pattern of their wolf ancestors. Dogs learned to thrive on high starch and high fat meals as they scavenged around human encampments, later assimilating into such human dwellings.
Using population genetic approaches, a study in “Nature Communications” described that metabolism genes and those for digestion underwent positive selection in dogs as they were domesticated.
The AMY2B gene encodes alpha-amylase 2B. This enzyme is important for starch digestion.
Savolainen reported the gene AMY2B was increased in copy number as wolves got domesticated and evolved into dogs.
However, an interesting question evolutionary biologists ask is “whether these evolutionary changes appeared in dogs during their initial domestication, or did they occur later as their humans transitioned from their hunter-gatherer lifestyle into agrarian sedentary dwellers?”
For the AMY2B copy number gain, authors suggest it was associated with the advent of agriculture. This makes sense, because even early human diets became starch-heavy as we learned to artificially grow crops, especially rice.
Some other traits in dogs, like their relatively smaller size as compared to wolves, likely evolved as their human companions settled down to farm at one location, and hunting was no longer the primary food source.
Another major divergence was in the neurology and behavior of evolving dogs in comparison to the ancestral wolf population.
Dogs are far more sociable and affectionate than wolves. So, it makes sense that when scientists compared dog and wolf genetics, they found differences in the genes for receptors of the hormone oxytocin, which promotes bonding and affection.
Additionally, epigenetic variations were also discovered between wolf and dog oxytocin receptors.
Some authors proposed that epigenetic changes in evolving wolves brought about a cascade of neurobehavioral transitions that have facilitated domestication.
Dogs’ genomes show a higher genetic capacity for synaptic plasticity, which brings about learning and memorization. Synaptic plasticity is also considered by biologists to have contributed to tameness and less fear and nervousness of dogs around humans.
Further, the biosynthesis of fight-or-flight response mediators adrenaline and noradrenaline has also undergone changes in ancestral wolves as they slowly became the dogs of today.
This ultimately improved emotional stability in dogs which was critical in their evolution as safe and trustworthy companions of early humans. This theory is called “Active Social Domestication.”
Scientists sought to answer how dog domestication shaped human evolution.
Some evolutionary biologists think early humans might have propelled themselves a long way in the path of civilization by keenly watching some of the behaviors of their furry pets.
For example, ancient humans perhaps realized that coordinated social partnerships, as their wolf-like dogs displayed, might be beneficial in more than one way.
Some authors argue that communal altruistic behaviors, like traits of caring for the old and the babies in the group, hunting and sharing food as a society and guarding themselves and their territory from predators were picked up by prehistoric human ancestors from their dog-like pets.
As with dogs, oxytocin plays a pivotal role in human bonding. Co-evolution of human and dog oxytocin signaling pathways has been a longstanding theory.
Further, just as dogs over millennia have learned to follow human expressions, humans also are believed to understand no other animal as much as they comprehend dog behavior. This has provoked the notion of psychological convergence between dogs and humans as they evolved to bond together.
Indeed, molecular genetic analyses have identified more than 300 genes that have co-evolved in early humans and dogs.
Therefore, dogs over centuries became genetically predisposed to many human diseases such as cancer, obesity, diabetes etc., in fact with even similar pathophysiological underpinnings.
It is not without reason that scientists consider dog domestication as a red-letter event in human history. This event has phenomenally dictated the evolutionary fate of both humans and their furry pets.
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