6
Delicate Interactions
The cross-fostering genetics experiment combined with rapid development of the close bond between Lyudmila and Pushinka was like the evolution of the human-dog relationship being accelerated to warp speed. That the artificial selection for tameness could catalyze such a profound change in an animal’s behavior, from the natural inclination to live as a loner in adulthood to forming such strong attachment, and with an animal from another species no less, is remarkable. How quickly this same change came about in wolves is impossible to know, but both genetic and archeological evidence suggests that a deeper bond than we developed with any other animal formed between us and wolves, or wolf-like proto-dogs, at least thousands of years ago, and perhaps tens of thousands of years ago. So close has the relationship been for so long that some experts argue that our two species coevolved, meaning that we acquired genetic adaptations to living with one another. Life with dogs, it seems, has been bred in our DNA, and life with humans has been bred into theirs.
A powerful testament to how far back in time the human-dog bond developed, and how strong it quickly became, is the wealth of ancient dog burials that have been discovered all over the world. Many of our prehistoric ancestors buried their dogs in graves just like the ones in which they buried their human loved ones, and sometimes in the same grave with their human masters. In fact, they began doing so right from the time dogs are generally thought to have been first fully domesticated, about 14,000 to 15,000 years ago.
The earliest find of a dog burial so far, dated to between 14,100 and 14,600 years ago, was discovered in the German town of Bonn-Oberkassel. The grave contained the fragmentary remains of a female dog buried along with the bones of a man aged fifty and a woman aged twenty, thought to have been the dog’s masters. A burial that evokes the closeness of the relationship more vividly is a site in the Jordan Valley dating to 12,000 years ago. A grave was found at the entrance to a home, marked by a large stone slab, with a human skeleton curled up on its right side, ritually placed in a sleeping position, with the left arm stretched out and resting on the skeleton of a dog puppy, as if in an embrace. A number of dog burials that indicate the great importance of dogs in the life of one community were found at a site in Siberia, on the shores of Lake Baikal, dating to 7,000 to 8,000 years ago. There the dogs were clearly laid to rest with great care, and some were buried with valuable objects. A number of dogs were buried with spoons and knives carved from deer antlers, and one was buried with a necklace made of deer teeth around its neck, as worn by the people in the area. In one grave, a man was buried with two dogs, one laid out on each side of him.
These graves suggest that while dogs were undoubtedly of great use to these early societies, likely as pack animals, guards, and partners in hunting, the nature of the relationship had developed far beyond a purely utilitarian affair. Many experts believe these burials indicate that dogs were seen as spiritual beings who should be treated with the same respect in death as humans.1 Good support for this comes from the Lake Baikal site, as not only were valuable items buried with the dogs there, but the people who lived there were foragers, relying heavily on fish and seals from the lake for their subsistence, so they probably didn’t need their dogs to help them hunt.
Why were our ancestors so enamored of dogs, and why did they hold them in such esteem? One reason may be that for thousands of years, they were the only wild animal to become domesticated, which would have been reason to believe there was something special about them. Conservative estimates that dogs were domesticated 14,000 to 15,000 years ago make them the domesticate for about 5,000 years, until sheep and cats also made the transition sometime around 10,500 years ago, followed in comparatively rapid succession by goats, about 10,000 years ago, and both pigs and cows about 9,000 years ago.2
A number of recent archeological finds suggest that dogs and humans have lived together for many thousands of years longer than was previously thought, and some intriguing new findings in genetics suggest that in the course of our long time together, we became increasingly good for each other’s well-being. Perhaps the most evocative of the archeological finds is a set of fossilized footprints on the floor of Chauvet cave in France, famed for its elaborate wall paintings of fierce predators, including lions, panthers, and bears, which date to approximately 26,000 years ago. Alongside a trail of prints left by a boy, estimated to have been about ten years old, run another set of prints, those of a large canid animal, and the prints suggest that this may have been an animal more like a dog than a wolf.3 It’s enchanting to imagine that boy with his proto-dog loyally trotting along by his side, and the images of fearsome predators that line the cave’s walls leave little doubt about why a wolf-dog companion would have been welcomed. A still earlier date for the presence of dogs, or dog-like ancestors, in our lives has been suggested on the basis of a dog-like skull found at another cave, in Belgium, which dates to approximately 31,700 years ago.4
As we lived together for so many eons, through so many changes in our environment and lifestyle, with humans developing from hunter-gatherers, to farmers, to urban dwellers, and our dogs coming along with us on the journey, our genomes adapted in complex and similar ways, both to each other and to the environment. For example, genetic adaptations similar to those in the human genome that allowed our ancestors to begin eating starchy foods, like the wheat, barley, and rice they domesticated, also appear in the dog genome, and they allowed dogs to eat these foods as well, perhaps first having scavenged them from our ancestors’ fields or stockpiles, and later being fed them. Wolves, who eat a meat-heavy diet, don’t have the complex genetic machinery to eat these grains.5
That we adapted specifically to life with one another is also attested to by a number of positive effects we have on each other. Many studies have shown that living with dogs has many beneficial physical and psychological effects on us, such as lowering our blood pressure and rates of heart disease, as well as the frequency with which we go to doctors, and increasing our general sociability, while also helping us fight off depression. Recent work on the neurotransmitter oxytocin confirms what every dog owner already knows—that we and our dogs genuinely enjoy each other’s company. Both sides feed off it in a positive feedback loop, in a kind of feel-good snowball of mutual reinforcement.
Researchers have known for more than four decades that oxytocin is fundamental in the bonding between human mothers and their children (as well as in nonhuman mother-child bonds).6 More recent work has found that when a human mother and her newborn engage in mutual gazing, oxytocin levels in the mom rise, and the newborn’s oxytocin system kicks into high gear. This leads to more gazing from the infant, which again increases the mother’s oxytocin level.7 When this work was published in 2014, we already knew something about the role that oxytocin plays in dog-owner interactions: when we pet our dogs, oxytocin levels rise in both us and them.8 But now we know even more: a 2015 study has shown that the mother-child oxytocin loop that turns on as a result of human mutual gazes is also at play with owners and their dogs. This study found that when dogs and owners simply gaze at one another, oxytocin levels go up in both. This leads to increased petting and more oxytocin in response to that petting, in a chemical lovefest. What’s more, if you spray oxytocin up a dog’s nose, and researchers do, it gazes longer at its owner, setting off another lovefest. None of this happens when you replace dogs with wolves in this experiment, the discovery of which must have required steely bravery on the part of the researchers.9
These biological effects dogs and their humans have on one another are brought about by changes in the genes that control the production of hormones and neurochemicals in our systems. They constitute additional strong support for Dmitri Belyaev’s theory that selection for tameness would unleash a cascade of changes in the production of the chemicals that regulate bodily functions. Dmitri had emphasized changes in the production of hormones in his theory at the start, because much less was understood about neurochemi
cals, like oxytocin, when he first formulated his theory. As research in the 1970s began revealing the powerful role they play in regulating an animal’s behavior, particularly illuminating their effects on how happy or depressed an animal is, Dmitri realized that they might also be integral to the changes brought about by destabilizing selection. The rapidly emerging understanding of how sensitive animal behavior is to changes in the levels of these chemicals coursing through our brains and throughout our bodies helped to explain why the behavior of the tame foxes had changed so rapidly, and why Lyudmila and Pushinka had developed such a strong bond.
For the first decade of the fox experiment, Dmitri and Lyudmila had not been able to investigate much about how the biochemistry of the tame foxes was changing. Their finding of much lower levels of stress hormones in the tame foxes was a strong start. But more work had to wait for methods of measuring, and manipulating, the levels of these chemicals to be developed. As great progress was made on this front in the 1970s Lyudmila and Dmitri were able to make many more important discoveries.
ONE OF THE IMPORTANT NEW FINDINGS CONCERNED the neurochemical serotonin. Discovered in the 1930s, serotonin was first identified as a muscle constrictor, helping to tone muscle, hence its name, which is shorthand for “toning serum.”10 But in the early 1970s, the fact that higher levels of serotonin in the brain lead to an elevated mood and less anxiety was discovered, and in 1974, the year Lyudmila and Pushinka moved into the house, Prozac, the first serotonin-based antidepressant, burst onto the scene. The new understanding of serotonin’s effects led Belyaev to believe that the tame foxes might appear so happy in part because they were producing higher levels of the neurochemical. Lyudmila ran tests of the serotonin levels in the blood of the control and tame foxes and found that, sure enough, the level was significantly higher in the tame foxes. Not only did they seem happier, they were, or at the very least hormones suggest they were. The same is true for dogs compared to wolves: the former have much higher levels of serotonin.11
Another obvious candidate for Lyudmila and Dmitri to look into in their foxes was the hormone melatonin, which was known to regulate the timing of mating and reproduction in many species. It must have been involved, they speculated, with the elite females going into estrous earlier, and with the few cases of those who had done so more than once a year. Melatonin was thought to be involved in the timing of mating in animals because, in the wild, many animals begin to mate when the days begin getting longer, and melatonin production changes according to the amount of light an animal is exposed to. It rises and falls both from day to night and seasonally. During the day, the level goes down and when night comes, it rises. The change in the levels in an animal’s system, as days start getting longer again from winter to spring, was thought to be one trigger for mating in many species.
The control mechanism governing these changes in melatonin production is the tiny pineal gland, which is a light receptor buried deep inside the brain. For that reason, it was dubbed the “third eye,” and it was thought to be vital to life functions because it is located near the very center of the brain. Back in the seventeenth century, René Descartes had even conjectured that it was the “seat of the soul,” where thoughts are generated.12 But precisely what the gland did, other than sensing light, had remained a mystery. At last scientists discovered that it manufactures melatonin, as well as a number of other hormones. Researchers also found that changes in levels of melatonin were involved in the production of the sex hormones critical to the process of mating and reproduction, kicking their production into high gear.
Dmitri and Lyudmila decided to investigate whether changes in the amount of light the foxes were exposed to would affect the timing of when they became ready for mating. During the fall months, Lyudmila and her assistants exposed a group of both elite and control foxes to two and a half more hours of light a day than was normal for that time of year. At the start, Lyudmila didn’t have the technology for measuring their levels of melatonin, which was a very tricky procedure that had only recently been developed and required sophisticated expertise. But she did have the ability to measure the levels of sex hormones, which is much less complicated. She and her team ran an analysis and discovered that with increased light exposure, sex hormone levels did increase significantly, in both the control and elite foxes, but the effect was much more pronounced in the elites. What’s more, this was true for both females and males, which was one of the first significant changes in the sexual biology of the males that Lyudmila had seen. In fact, she found that the levels were so high in some of the tame foxes that when she examined them she discovered some were ready for mating, and this time, that was true for some males as well as females. This was a big new first for the fox study, as now Lyudmila could examine whether these elites could conceive more than once a year, one of the most radical changes brought about by domestication in other species. She carefully selected pairs for mating, but none of the females became pregnant. Clearly more was involved in regulating the reproduction process than the elevation of sex hormones.
Still, this was a major finding. It suggested that the tame female foxes, who had already been going into estrous earlier without the special exposure to more light, were producing different levels of melatonin than the rest of the foxes in response to the same amount of light. Whether they were producing more or less couldn’t be determined without measuring the levels of melatonin in the foxes’ systems. This was a conundrum. They’d have to find someone with the expertise. While one of the researchers at the Institute, Larissa Kolesnikova, was a specialist in the workings of the pineal gland, even she didn’t know the sophisticated methods for measuring melatonin.
Dmitri asked Larissa if she would be willing to join the fox team to work on this study and to get the training to do it. She’d have to travel outside of the Soviet Union for that, he told her, and the training would take several months. Larissa was intrigued by the challenge, allured by the opportunity to make a significant discovery. She also found the prospect of working closely with Dmitri Belyaev of great appeal, recalling, “you know, there was the attraction to working with him . . . more attractive than my feeling of insecurity.”13 She agreed to go. But sending her overseas wasn’t so simple. Now Dmitri had to get her the clearance to travel and find the funds to pay for the training. Despite the isolation and the relative paucity of funding that the Cold War had imposed on Russian scientists, he was determined to be at the forefront of that work, and he had the power as the head of a major institute to get things done. He arranged for Larissa to travel to the University of San Antonio Health Center, where cutting edge work on measuring melatonin levels was underway.
Learning the technique was only half the battle of measuring the melatonin levels, though. Larissa would have to take samples of the foxes’ blood, both during the day and late at night, right before the normal reproductive season in late January, when the key changes in melatonin production were thought to occur. Getting samples during the day wouldn’t be any particular ordeal, but winter nights in Siberia are often brutally cold. The temperature regularly drops to −40°F. Larissa told herself she’d just have to focus on the beauty of the nights, with moonlight glinting off the snow, turning it, as she recalls, “bluish, lilac, and purplish shades,” and a stunning display of stars “looking so far, far away.”14 But there was another problem. She couldn’t do the work alone, the caretakers would have to help her. They had helped with this sort of work before, measuring stress hormone levels. But that was done only during the day.
Most of the caretakers were women with families to take care of. Larissa would be asking them to leave their homes and families and come to the farm for several hours, from 11 p.m. until 2 a.m., for two weeks. She fondly recalls, “I do not remember anybody complaining that she could not put a kid to the bed, or would not have time to cook for the next day . . . Their motto was ‘If it is for science, let’s do it.’”
On a bitterly cold night, the driver of the Institu
te van, a genial fellow named Valery, picked Larissa up at her apartment in Akademgorodok a few minutes before 11 p.m. and then headed over to the little town of Kainskaya Zaimka to pick up the workers. Larissa remembers that every one of them was waiting for the van, standing at the windows watching for it to pull up. They knew timing was tight and they didn’t want to be responsible for slowing things up.
When he pulled up next to the rows of sheds at the fox farm, Valery put the van in park and kept the engine running, settling in for a nap while Larissa and the others considered the list Lyudmila had written that day of the foxes to be sampled. They had to map out their route for the night so that they could move as fast as possible. Heavy snow had just fallen, and the first thing they had to do was shovel paths to the sheds and over to the lab, where they would carry the foxes for the sampling. The night was virtually pitch black, with very little moonlight, so some of the women had to hold flashlights Lyudmila had provided. Making their way through the sheds, they hurried to locate the right foxes, shining the flashlights on the nameplates above their cages. Then holding the blessedly warm foxes tightly in their arms, they rushed from the sheds to the lab and back, as though engaged in some kind of clandestine military operation. When the sampling was done, they all ran to the van and Larissa recalls how, “Valery opened the door for us, laughing and asking if we were completely frozen or not yet.”
After the blood samples were analyzed, Larissa met with Lyudmila and Dmitri and told them that she’d discovered a curious thing: the amount of melatonin circulating in the blood of the tame foxes was no different than in the control foxes. What was different, though, was the level of melatonin in the pineal gland. It was much higher in the tame animals.15 This result was very strange, she said. The tame foxes were making much more melatonin, as expected, but it was amassing in their pineal glands in a kind of crystalized form so that it was “stuck,” unable to make its way to the bloodstream. The elites’ pineal glands were also found to be much smaller, about half the size, of those of the control foxes. Exactly what could be causing all this, none of them had any idea.
How to Tame a Fox (and Build a Dog) Page 13
